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1.
  • Karimi, Mohammad Taghi, et al. (författare)
  • Evaluation of the hip joint contact force in subjects with Perthes based on OpenSIM
  • 2019
  • Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 67, s. 44-48
  • Tidskriftsartikel (refereegranskat)abstract
    • The head of femoral bone is deformed in the subjects with Leg Calve Perthes disease (LCPD). This may be due to the excessive loads applied on it. There are no studies that report the hip joint contact force in subjects with LCPD. Therefore, the aim of this study was to evaluate the hip joint contact force in subjects with Perthes disease. Ten typically-developing (TD) children and 10 children with LCPD were recruited in this study. The kinematics and kinetics of the subjects were evaluated in 3D motion analysis. The hip joint contact force was approximated using OpenSIM software. Differences were determined with an independent t-test. There was a significant difference between walking speed of TD and Perthes subjects (63.8 (±8.1) and 57.4 (±7.0) m/min, respectively). The first peak of hip joint contact force was 4.8 (±1.7) N/BW in Perthes subjects, compared to 7.6 (±2.5) N/BW in TD subjects (p = 0.004). The peak hip joint contact force in mediolateral and anteroposterior directions was significantly lower in Perthes subjects (p < 0.05). The hip joint excursion was 40.0 (±5.6) and 46.4 (±8.5) degrees in Perthes and normal subjects, respectively (p = 0.03). The hip joint contact forces were lower in the subjects with Perthes disease. Therefore, it can be concluded that the strategies used by LCPD subjects were successful to decrease hip joint contact force.
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2.
  • Örtqvist, Maria, et al. (författare)
  • Reliability of a new instrument for measuring plantarflexor muscle strength
  • 2007
  • Ingår i: Archives of Physical Medicine and Rehabilitation. - : Elsevier BV. - 0003-9993 .- 1532-821X. ; 88:9, s. 1164-1170
  • Tidskriftsartikel (refereegranskat)abstract
    • Objectives: To test the reliability of a new muscle strength testing instrument (the Strength Measuring Chair [SMC]) designed to quantify isometric strength in the lower extremities, and to determine the agreement between the SMC and an isokinetic dynamometer (Biodex). Design: Isometric strength tests were performed in plantar-flexors with 2 different knee positions (60 degrees, 30 degrees). Measurements were taken at 3 different sessions. Setting: Strength testing laboratory. Participants: Twenty-three able-bodied adults and 15 able-bodied children. Interventions: Not applicable. Main Outcome Measure: Isometric plantarflexor strength. Results: The reliability of isometric strength measurements of plantarflexors taken in the SMC was excellent for both the adult and children groups (intraclass correlation coefficient range,.84-.87). A Bland-Altman 95% limit of agreement test showed no systematic variation in 3 of the 4 SMC test observations; systematic variation was only observed in the adult group at a knee position of 30 degrees. There was no systematic difference in the adult group between the SMC and the isokinetic dynamometer, but there was a systematic variation in the children's group. Conclusions: The SMC reliably measured isometric plantarflexor strength in the tested populations.
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3.
  • Alm, M., et al. (författare)
  • Clinical evaluation of seating in persons with complete thoracic spinal cord injury
  • 2003
  • Ingår i: Spinal Cord. - : Springer Science and Business Media LLC. - 1362-4393 .- 1476-5624. ; 41:10, s. 563-571
  • Tidskriftsartikel (refereegranskat)abstract
    • Study Design: Consecutive male patients studied with photographic measurement of a combination of clinical methods. Objectives: To describe seating in individuals with complete thoracic spinal cord injury (SCI) by using a combination of clinical methods. Setting: Spinalis SCI unit, Stockholm, Sweden. Methods: Wheelchair specifications were documented. Measurements of posture from photographs in 30 male subjects with complete thoracic SCI, sitting in a relaxed and an upright position on a standardized surface and in a wheelchair were calculated. A comparison was made between positions and seating surfaces. An examiner's classification of lower trunk position in wheelchair was compared to subjects' evaluations. SCI subjects reported sitting support, satisfaction, and wishes for improvement. Results: Most SCI subjects used similar wheelchair specifications. None of the backrests were custom designed. Relatively small differences were found between the relaxed and upright position in the wheelchair regarding measurements of posture and according to the examiner's classification of the lower trunk position. Only 13/30 SCI subjects were sitting with the lower trunk centered relative to the backrest in the upright position. The examiner's classification and the subjects' evaluation of asymmetric sitting were not always in agreement. Only 12/30 SCI subjects were satisfied with their way of sitting. Conclusion: Current wheelchair specifications and adjustments seem to inhibit a postural correction towards upright sitting and fail to provide sufficient lateral support. Findings indicate an inability for SCI subjects to vary their sitting position in a wheelchair to a large extent. Both an examiner's classification and subjects' evaluation of asymmetric sitting are necessary to obtain a sufficient knowledge base for subsequent adjustment. By using methods regarding different aspects of seating, a more comprehensive view of seating was achieved. The combination of clinical methods seems to be useful in order to describe seating in individuals with complete thoracic SCI.
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5.
  • Bartonek, Asa, et al. (författare)
  • A new carbon fibre spring orthosis for children with plantarflexor weakness
  • 2007
  • Ingår i: Gait & Posture. - : Elsevier BV. - 0966-6362 .- 1879-2219. ; 25:4, s. 652-656
  • Tidskriftsartikel (refereegranskat)abstract
    • We tested a new orthosis with a carbon fiber spring constructed to enable energy storing during increasing dorsiflexion in mid-stance, and to use the energy at the end of stance phase to aid push-off. The orthosis was tested on children with plantarflexor weakness due to motor disorders. All subjects were tested with 3D gait analysis with both the new orthosis and with their regularly used orthosis. In this technical note, the results of three individuals are reported. The preliminary findings show increased dorsiflexion, altered knee kinematics and improved kinetic and temporo-spatial parameters. Although the carbon spring orthosis influenced the subjects' gait in different ways, we conclude that the tested subjects with plantarflexion weakness benefit from the carbon fiber spring orthoses during walking. The parents' and children's subjective impressions as acquired from a questionnaire were also positive.
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6.
  • Bartonek, Asa, et al. (författare)
  • Effects of carbon fibre spring orthoses on gait in ambulatory children with motor disorders and plantarflexor weakness
  • 2007
  • Ingår i: Developmental Medicine & Child Neurology. - : Wiley. - 0012-1622 .- 1469-8749. ; 49:8, s. 615-620
  • Tidskriftsartikel (refereegranskat)abstract
    • A consecutive series of 17 children (six males, 11 females; mean age 11y 11mo [SD 4y 5mo]; range 3y 11mo-17y 4mo) with plantarflexor weakness was assessed to compare gait differences between a carbon fibre spring orthosis (CFSO) and participants' regular orthoses. Twelve children had myelomeningocele, four children had arthrogryposis, and one child had neuropathy with peripheral muscle pareses. All participants underwent clinical examination and 3D gait analysis. Parents answered a questionnaire to assess subjective perceptions of the orthoses. Results from 3D gait analysis provided evidence that CFSOs enhance gait function in most participants by improving ankle plantarflexion moment (p < 0.001), ankle positive work (p < 0.001), and stride length (p < 0.001). The CFSO did not suit all participants, which emphasizes the importance of analyzing each patient's needs.
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7.
  • Bartonek, Asa, et al. (författare)
  • Head and Trunk Movements During Turning Gait in Children with Cerebral Palsy
  • 2019
  • Ingår i: Journal of motor behavior. - : ROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD. - 0022-2895 .- 1940-1027. ; 51:4, s. 362-370
  • Tidskriftsartikel (refereegranskat)abstract
    • Thirty children with cerebral palsy (CP) and 22 typical developing (TD) were tested with 3D-gait analysis. At turning, trunk rotation was larger in CP2 (GMFCS II) than in TD and CP1 (GMFCS I), and head flexion was larger in CP3 (GMFCS III) than TD. Maximum head and trunk flexion values during the entire trial were larger in CP3 than in the other groups, and trunk flexion was larger in CP2 than in TD. Trial time increased with GMFCS-level. Less trunk rotation than TD and CP1 reflects spatial insecurity in CP2, which in CP3 is compensated by the walker. The flexed head and trunk in CP3 and trunk in CP2 may reflect deficits in proprioception and sensation requiring visual control of the lower limbs.
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8.
  • Bartonek, A., et al. (författare)
  • Influence of external visual focus on gait in children with bilateral cerebral palsy
  • 2016
  • Ingår i: Pediatric Physical Therapy. - 0898-5669 .- 1538-005X. ; 28:4, s. 393-399
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: To explore whether focusing a target influenced gait in children with cerebral palsy (CP) and typical development (TD). Methods: Thirty children with bilateral CP (Gross Motor Function Classification System [GMFCS] I-III) and 22 with TD looked at a light at walkway end (Gaze Target) while walking and returned (No Target). Results: During Gaze versus No Target, children with TD reduced temporal-spatial parameters and movements in the sagittal (SPM) and transverse planes. In comparison, during Gaze Target, children in CP1 (GMFCS I) had larger trunk SPM, children in CP2 (GMFCS II) larger neck (SPM), and children in CP3 (GMFCS III) greater head and neck frontal plane movements, and reduced cadence and single support. Conclusions: Focusing a target altered gait in children with CP. Children in CP1 reduced movements similar to children with TD, children in CP2 behaved nearly unchanged, whereas children in CP3 reduced movements and temporalspatial parameters, potentially as a consequence of lack of sensory information from lower limbs.
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9.
  • Bartonek, Asa, et al. (författare)
  • Influence of heel lifts during standing in children with motor disorders
  • 2011
  • Ingår i: Gait & Posture. - : Elsevier BV. - 0966-6362 .- 1879-2219. ; 34:3, s. 426-431
  • Tidskriftsartikel (refereegranskat)abstract
    • Heel wedges may influence standing posture but how and to what extent are unknown. Thirty-two children with motor disorders - 16 with arthrogryposis multiplex congenita (AMC) and 16 with cerebral palsy (CP) - and 19 control children underwent a three-dimensional motion analysis. Unassisted standing during 20s with shoes only and with heel lifts of 10,20 and 30 mm heights was recorded in a randomized order. The more weight-bearing limb or the right limb was chosen for analysis. In both the AMC and CP groups, significant changes were seen between various heel lifts in ankle, knee and pelvis, and in the control group in the ankle only. Between orthosis and non-orthosis users significant differences were seen between different heel lift conditions in ankle, knee and trunk in the AMC group and in the ankle in the CP group. Pelvis position changed toward less anterior tilt with increasing heel height, but led to increasing knee flexion in most of the children, except for the AMC Non-Ort group. Children with AMC and CP represent different motor disorders, but the heel wedges had a similar influence on pelvis, hip and knee positions in all children with CP and in the AMC orthosis users. A challenge is to apply heel heights adequate to each individual's orthopaedic and neurologic conditions to improve biomechanical alignment with respect to all body segments.
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10.
  • Bartonek, A., et al. (författare)
  • The influence of spasticity in the lower limb muscles on gait pattern in children with sacral to mid-lumbar myelomeningocele : a gait analysis study
  • 2005
  • Ingår i: Gait & Posture. - : Elsevier BV. - 0966-6362 .- 1879-2219. ; 22:1, s. 10-25
  • Tidskriftsartikel (refereegranskat)abstract
    • Gait analysis and recording of standing position were performed in 38 ambulatory children with myelomeningocele. Thirty-four were independent ambulators and four required a walking aid. All subjects were assigned one of four muscle function groups based on muscle strength. They were also divided into subgroups based on the distinction between flaccid and spastic paresis in the lower limb joints. A comparison was made between the gait pattern of the children with spasticity and that of the children with flaccid paresis in each muscle function group. Spasticity in only the ankle joint muscles influenced the subject's gait and standing position compared to the subgroups with a flaccid paresis. Even larger deviations in gait and standing position were observed when spasticity occurred in muscles at the knee and hip joints. When setting ambulatory goals the presence of additional neurological symptoms such as spasticity and inadequate balance should be taken into consideration.
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12.
  • Brorsson, Sofia (författare)
  • Biomechanical studies of finger extension function. Analysis with a new force measuring device and ultrasound examination in rheumatoid arthritis and healhty muscles
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Aims: The overall aim of this thesis was to further our understanding of extensor muscles and their role for hand function. The aims of the studies were: To develop and evaluate a new device for finger extensor force measurements. To evaluate ultrasound as a tool for assessment of muscle architecture. To determine the correlation between extensor muscle force and hand function. To evaluate the degree of impaired finger extensor force in rheumatoid arthritis (RA) and the correlation to impaired hand function. To analyse the effect of hand exercise in RA patients and healthy subjects with ultrasound and finger extension force measurements. Method: A new finger extension force measuring device was developed and an ultrasound based method was used to be able to objectively measure the finger extension force and analyze the static and dynamic extensor muscle architectures. Measurements were made of healthy volunteers (n=127) and RA patients (n=77) during uninfluenced and experimental conditions. A hand exercise program was performed and evaluated with hand force measurements, hand function test, patient relevant questionnaires (DASH and SF-36) and ultrasound measurements. Results: The new finger extension force measurement device was developed and then validated with measurements of accuracy as well as test-retest reliability. The coefficient of variation was 1.8 % of the applied load, and the test-retest reliability showed a coefficient of variation no more than 7.1% for healthy subjects. Ultrasound examination on m. extensor digitorum communis (EDC) showed significant differences between healthy men and healthy women as well as between healthy women and RA patients. The extension and flexion force improved in both groups after six weeks of hand exercise (p<0.01). Hand function improved in both groups (p<0.01). The RA group showed improvement in the results of the DASH questionnaire (p<0.05). The cross-sectional area of the EDC increased significantly in both groups. Conclusions: A new finger extension force measuring device has been developed which provides objective and reliable data on the extension force capacity of normal and dysfunctional hands and is sufficiently sensitive to evaluate the effects of hand exercise. US provide useful information about muscle architecture. A significant improvement of hand strength and hand function in RA patients was seen after six weeks of hand training, the improvement was even more pronounced after 12 weeks. Hand exercise is thus an effective intervention for RA patients, providing better strength and function.
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13.
  • Broström, Eva, et al. (författare)
  • Trunk and center of mass movements during gait in children with juvenile idiopathic arthritis
  • 2007
  • Ingår i: Human Movement Science. - : Elsevier BV. - 0167-9457 .- 1872-7646. ; 26:2, s. 296-305
  • Tidskriftsartikel (refereegranskat)abstract
    • Motion of the body center of mass (CoM) can often indicate the overall effect of the strategy of forward progression used. In the present study, focus is placed on trunk movements in the sagittal, coronal, and transverse/rotation plane, as well as placement of the CoM, during gait in children with juvenile idiopathic arthritis (JIA). Seventeen children with JIA, all with polyarticular lower extremity involvement were examined before and approximately two weeks after treatment with intra-articular cortico-steroid injections. Movement was recorded with a 6-camera 3D motion analysis system in both the children with JIA and in 21 healthy controls. Trunk and center of mass movements were compared between JIA and controls, and effects of intra-articular cortico-steroid treatment were evaluated. Children with JIA were more posteriorly tilted in the trunk, contrary to the common clinical impression, and had their CoM placed more posterior and off-centred, which may have been a result of pain. With such knowledge, it might be possible to better understand the effects of their pain and involvement, and ultimately to plan a treatment strategy for improving their gait patterns.
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14.
  • Dijkstra, Erik J., et al. (författare)
  • Computation of ground reaction force using Zero Moment Point
  • 2015
  • Ingår i: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 48:14, s. 3776-3781
  • Tidskriftsartikel (refereegranskat)abstract
    • Motion analysis is a common clinical assessment and research tool that uses a camera system or motion sensors and force plates to collect kinematic and kinetic information of a subject performing an activity of interest. The use of force plates can be challenging and sometimes even impossible. Over the past decade, several computational methods have been developed that aim to preclude the use of force plates. Useful in particular for predictive simulations, where a new motion or change in control strategy inherently means different external contact loads. These methods, however, often depend on prior knowledge of common observed ground reaction force (GRF) patterns, are computationally expensive, or difficult to implement. In this study, we evaluated the use of the Zero Moment Point as a computationally inexpensive tool to obtain the GRFs for normal human gait. The method was applied on ten healthy subjects walking in a motion analysis laboratory and predicted GRFs are evaluated against the simultaneously measured force plate data. Apart from the antero-posterior forces, GRFs are well-predicted and errors fall within the error ranges from other published methods. Joint extension moments were underestimated at the ankle and hip but overestimated at the knee, attributable to the observed discrepancy in the predicted application points of the GRFs. The computationally inexpensive method evaluated in this study can reasonably well predict the GRFs for normal human gait without using prior knowledge of common gait kinetics.
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15.
  • Dijkstra, Erik J. (författare)
  • Constrained Optimization for Prediction of Posture
  • 2016
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The ability to stand still in one place is important in a variety of activities of daily living. For persons with motion disorders, orthopaedic treatment, which changes geometric or biomechanical properties, can improve the individual'sposture and walking ability. Decisions on such treatment require insight in how posture and walking ability are aected, however, despite expectations based on experience, it is never a-priori known how a patient will react to a treatment. As this is very challenging to observe by the naked eye, engineering tools are increasingly employed to support clinical diagnostics and treatment planning. The development of predictive simulations allows for the evaluation of the eect of changed biomechanical parameters on the human biological system behavior and could become a valuable tool in future clinical decision making. In the first paper, we evaluated the use of the Zero Moment Point as a computationally inexpensive tool to obtain the ground reaction forces (GRFs) for normal human gait. The method was applied on ten healthy subjects walking in a motion analysis laboratory and predicted GRFs are evaluated against the simultaneously measured force plate data. Apart from the antero-posterior forces, GRFs are well-predicted and errors fall within the error ranges from other published methods. The computationally inexpensive method evaluated in this study can reasonably well predict the GRFs for normal human gait without using prior knowledge of common gait kinetics. The second manuscript addresses the complications in the creation and analysis of a posture prediction framework. The fmincon optimization function in MATLAB was used in conjunction with a musculoskeletal model in OpenSim. One clear local minimum was found in the form of a symmetric standing posture but perturbation analyses revealed the presence of many other postural congurations, each representing its own unique local minimum in the feasible parameter space. For human postural stance, this can translate to there being many different ways of standing without actually noticing a difference in the efforts required for these poses.
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16.
  • Dijkstra, Erik J., et al. (författare)
  • Sensitivity in prediction of human posture by constrained optimization
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • In a variety of activities of daily living, it is important to be able to stand still in one place. For persons with motion disorders, orthopaedic treatment, which changes geometric or biomechanical properties, can improve the individual's posture and walking ability. Such treatment requires insight into how posture and walking ability are affected. As this is very challenging to observe by the naked eye, engineering tools are increasingly employed to support clinical diagnostics and treatment planning. Because of their potential to help unravel the causal relation between treatment and its outcome, the number of predictive methods are increasing. This study addresses the complications in the creation and analysis of a posture prediction framework. The fmincon optimization function in MATLAB was used in conjunction with a musculoskeletal model in OpenSim. One clear local minimum was found in the form of a symmetric standing posture but perturbation analyses revealed the presence of many other postural congurations, each representing its own unique local minimum in the feasible parameter space. For human postural stance, this can translate to there being many different ways of standing without actually noticing a difference in the efforts required for these poses.
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17.
  • Engström, Pähr, et al. (författare)
  • Botulinum toxin A does not improve cast treatment for idiopathic toe-walking - a randomized controlled trial
  • 2013
  • Ingår i: Journal of Bone and Joint Surgery. American volume. - 0021-9355 .- 1535-1386. ; 95:5, s. 400-407
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: There are many treatments for idiopathic toe-walking, including casts with or without injection of botulinum toxin A. Combined treatment with casts and botulinum toxin A has become more common even though there have been few studies of its efficacy and safety problems. Our aims were to conduct a randomized controlled trial to test the hypotheses that combined treatment with casts and botulinum toxin A is more effective than casts alone in reducing toewalking by patients five to fifteen years of age, and that the treatment effect correlates with the extent of coexisting neuropsychiatric problems. Methods: All patients who had been consecutively admitted to the pediatric orthopaedics department of our institution because of idiopathic toe-walking between November 2005 and April 2010 were considered for inclusion in the study. Forty-seven children constituted the study population. The children were randomized to undergo four weeks of treatment with below-the-knee casts either as the sole intervention or to undergo the cast treatment one to two weeks after receiving injections of botulinum toxin A into the calves. Before treatment and three and twelve months after cast removal, all children underwent three-dimensional (3-D) gait analysis. The severity of the idiopathic toe-walking was classified on the basis of the gait analysis, and the parents rated the time that their child spent on his/her toes during barefoot walking. Passive hip, knee, and ankle motion as well as ankle dorsiflexor strength were measured. Before treatment, all children were evaluated with a screening questionnaire for neuropsychiatric problems. Results: No differences were found in any outcome parameter between the groups before treatment or at three or twelve months after cast removal. Several gait-analysis parameters, passive ankle motion, and ankle dorsiflexor strength were improved at both three and twelve months in both groups, even though many children still demonstrated some degree of toe-walking. The treatment outcomes were not correlated with coexisting neuropsychiatric problems. Conclusion: Adding botulinum toxin-A injections prior to cast treatment for idiopathic toe-walking does not improve the outcome of cast-only treatment. Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.
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18.
  • Engström, Pähr, et al. (författare)
  • Does Botulinum toxin A improve the walking pattern in children with idiopathic toe-walking?
  • 2010
  • Ingår i: Journal of Children's Orthopaedics. - : SAGE Publications. - 1863-2521 .- 1863-2548. ; 4:4, s. 301-308
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Numerous recommendations have been made for treating idiopathic toe-walking (ITW), but the treatment results have been questioned. The purpose of this study was to investigate whether botulinum toxin A (BTX) improves the walking pattern in ITW as examined with 3-D gait analysis. Participants and methods: A consecutive series of 15 children (aged 5-13 years) were enrolled in the study. The children underwent a 3-D gait analysis prior to treatment with a total of 6 units/kg bodyweight Botox® in the calf muscles and an exercise program. The gait analysis was repeated 3 weeks and 3, 6, and 12 months after treatment. A classification of toe-walking severity was made before treatment and after 12 months. The parents rated the perceived amount of toe-walking prior to treatment and 6 and 12 months after treatment. Results: Eleven children completed the 12-month follow-up. The gait analysis results displayed a significant improvement, indicating decreased plantarflexion angle at initial contact and during swing phase and increased dorsiflexion angle during midstance at all post-treatment testing instances. According to the parents' perception of toe-walking, 3/11 children followed for 12 months had ceased toe-walking completely, 4/11 decreased toe-walking, and 4/11 continued toe-walking. After 6-12 months, the toe-walking severity classification improved in 9 of the 14 children for whom data could be assessed. Conclusions: A single injection of BTX in combination with an exercise program can improve the walking pattern in children with ITW seen at gait analysis, but the obvious goal of ceasing toe-walking is only occasionally reached.
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19.
  • Eriksson, Marie, et al. (författare)
  • Gait dynamics in the wide spectrum of children with arthrogryposis : a descriptive study
  • 2015
  • Ingår i: BMC Musculoskeletal Disorders. - : BioMed Central. - 1471-2474. ; 16
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Arthrogryposis Multiplex Congenita (AMC) is a heterogeneous condition characterized by multiple joint contractures at birth. Greater movements in the trunk and pelvis during walking have been observed in children with AMC using orthoses compared to those wearing only shoes. This study investigated gait dynamics in children with AMC and identified compensatory mechanisms that accommodate walking. Methods: Twenty-six children with AMC who walked with orthoses or shoes and a control group consisting of 37 typically-developing children were evaluated in 3D gait analysis. Children with AMC were divided into subgroups based on which joints needed to be stabilized in the sagittal plane; AMC1 used knee-ankle-foot orthoses (KAFOs) with locked knee joints, AMC2 used KAFOs with open knee joints or ankle-foot orthoses, and AMC3 used shoes. Results: The Gait Deviation Index was lower in AMC groups than in the control group, with the lowest in AMC1. Excessive trunk movements in frontal and transverse planes were observed in AMC2 and especially in AMC1. Lower hip flexion moment was found in AMC1, while AMC2 and AMC3 showed similar hip flexion moments as the control group. Knee extension moments were similar between the groups. In the frontal plane there were only small differences between the groups in hip abduction moment. A joint work analysis indicated greater contribution from the hip muscles to overall positive work in AMC groups, particularly in AMC1, than in the control group. Conclusion: All AMC groups showed less hip extension than the control group, but hip flexion moment was significantly lower only in AMC1, which can be attributed to their gait strategy with bilateral locked KAFOs. AMC1, who had weak knee extensors, were helped by their locked KAFOs and therefore showed similar knee extension moment as the other groups. This finding, together with their gait patterns, demonstrates the children's high reliance on hip muscles and presumably trunk muscles to provide propulsion. Our study shows that with adequate orthotic support, children with AMC and even with severe weakness and contractures can achieve walking.
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20.
  • Eriksson, Marie, et al. (författare)
  • Gait pattern in children with arthrogryposis multiplex congenita
  • 2010
  • Ingår i: Journal of Children's Orthopaedics. - : SAGE Publications. - 1863-2521 .- 1863-2548. ; 4:1, s. 21-31
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: Lower limb contractures and muscle weakness are common in children with arthrogryposis multiplex congenita (AMC). To enhance or facilitate ambulation, orthoses may be used. The aim of this study was to describe gait pattern among individuals wearing their habitual orthotic devices. Methods: Fifteen children with AMC, mean age 12. 4 (4. 3) years, with some lower limb involvement underwent 3-D gait analysis. Three groups were defined based on orthosis use; Group 1 used knee-ankle-foot orthoses with locked knee joints, Group 2 used ankle-foot orthoses or knee-ankle-foot orthoses with open knee joints and Group 3 used no orthoses. Results: The greatest trunk and pelvis movements in all planes and the greatest hip abduction were observed in Group 1, compared to Groups 2 and 3, as well as to the gait laboratory control group. Maximum hip extension was similar in Groups 1 and 2, but in Group 3, there was less hip extension and large deviations from the control data. Lower cadence and walking speed were observed in Group 1 than in Groups 2 and 3. The step length was similar in all groups and also with respect to the gait laboratory reference values. Conclusions: Children with AMC were subdivided according to orthoses use. Kinematic data as recorded with 3-D gait analysis showed differences among the groups in trunk, pelvis and knee kinematics, and in cadence and walking speed. The step length was similar in all groups and to the gait laboratory reference values, which may be attributable to good hip extension strength in all participants.
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21.
  • Forslund, Emelie Butler, et al. (författare)
  • A Protocol for Comprehensive Analysis of Gait in Individuals with Incomplete Spinal Cord Injury
  • 2024
  • Ingår i: Methods and Protocols. - : MDPI AG. - 2409-9279. ; 7:3
  • Tidskriftsartikel (refereegranskat)abstract
    • This is a protocol for comprehensive analysis of gait and affecting factors in individuals with incomplete paraplegia due to spinal cord injury (SCI). A SCI is a devastating event affecting both sensory and motor functions. Due to better care, the SCI population is changing, with a greater proportion retaining impaired ambulatory function. Optimizing ambulatory function after SCI remains challenging. To investigate factors influencing optimal ambulation, a multi-professional research project was grounded with expertise from clinical rehabilitation, neurophysiology, and biomechanical engineering from Karolinska Institutet, the Spinalis Unit at Aleris Rehab Station (Sweden's largest center for specialized neurorehabilitation), and the Promobilia MoveAbility Lab at KTH Royal Institute of Technology. Ambulatory adults with paraplegia will be consecutively invited to participate. Muscle strength, sensitivity, and spasticity will be assessed, and energy expenditure, 3D movements, and muscle function (EMG) during gait and submaximal contractions will be analyzed. Innovative computational modeling and data-driven analyses will be performed, including the identification of clusters of similar movement patterns among the heterogeneous population and analyses that study the link between complex sensorimotor function and movement performance. These results may help optimize ambulatory function for persons with SCI and decrease the risk of secondary conditions during gait with a life-long perspective.
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22.
  • Gutierrez-Farewik, Elena, 1973- (författare)
  • Botulinum toxin A does not improve cast treatment for idiopathic toe-walking-a randomized controlled trial
  • 2013
  • Ingår i: Journal of Bone and Joint Surgery. American volume. - 0021-9355 .- 1535-1386. ; 95:5, s. 400-407
  • Tidskriftsartikel (refereegranskat)abstract
    • ACKGROUND:There are many treatments for idiopathic toe-walking, including casts with or without injection of botulinum toxin A. Combined treatment with casts and botulinum toxin A has become more common even though there have been few studies of its efficacy and safety problems. Our aims were to conduct a randomized controlled trial to test the hypotheses that combined treatment with casts and botulinum toxin A is more effective than casts alone in reducing toe-walking by patients five to fifteen years of age, and that the treatment effect correlates with the extent of coexisting neuropsychiatric problems.METHODS:All patients who had been consecutively admitted to the pediatric orthopaedics department of our institution because of idiopathic toe-walking between November 2005 and April 2010 were considered for inclusion in the study. Forty-seven children constituted the study population. The children were randomized to undergo four weeks of treatment with below-the-knee casts either as the sole intervention or to undergo the cast treatment one to two weeks after receiving injections of botulinum toxin A into the calves. Before treatment and three and twelve months after cast removal, all children underwent three-dimensional (3-D) gait analysis. The severity of the idiopathic toe-walking was classified on the basis of the gait analysis, and the parents rated the time that their child spent on his/her toes during barefoot walking. Passive hip, knee, and ankle motion as well as ankle dorsiflexor strength were measured. Before treatment, all children were evaluated with a screening questionnaire for neuropsychiatric problems.RESULTS:No differences were found in any outcome parameter between the groups before treatment or at three or twelve months after cast removal. Several gait-analysis parameters, passive ankle motion, and ankle dorsiflexor strength were improved at both three and twelve months in both groups, even though many children still demonstrated some degree of toe-walking. The treatment outcomes were not correlated with coexisting neuropsychiatric problems.CONCLUSION:Adding botulinum toxin-A injections prior to cast treatment for idiopathic toe-walking does not improve the outcome of cast-only treatment.TRIAL REGISTRATION: ClinicalTrials.gov NCT01590693.
  •  
23.
  • Gutierrez Farewik, Elena M, 1973- (författare)
  • A new model for diffuse brain injury by rotational acceleration: II. Effects on extracellular glutamate, intracranial pressure, and neuronal apoptosis
  • 2001
  • Ingår i: Journal of Neurotrauma. - 0897-7151 .- 1557-9042. ; 18:3, s. 259-73
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study is to monitor excitatory amino acids (EAAs) in the extracellular fluids of the brain and to characterize regional neuronaldamage in a new experimental model for brain injury, in which rabbits were exposed to 180-260 krad/s2 rotational head acceleration. This loading causes extensive subarachnoid hemorrhage, focal tissue bleeding, reactive astrocytosis, and axonal damage. Animals were monitored for intracranial pressure (ICP) and for amino acids in the extracellular fluids. Immunohistochemistry was used to study expression of the gene c-Jun and apoptosis with the terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) technique. Extracellular glutamate, glycine, and taurine increased significantly in the hippocampus within a few hours and remained high after 24 h. Neuronal nuclei in the granule layers of the hippocampus and cerebellum were positive for c-Jun after 24 h. Little immunoreactivity was detected in the cerebral cortex. c-Jun-positive neuronal perikarya and processes were found in granule and pyramidal CA4 layers of the hippocampus and among the Purkinje cells of the cerebellum. Also some microglial cells stained positively for c-Jun. TUNEL reactivity was most intense at 10 days after trauma and was extensive in neurons of the cerebral cortex, hippocampus, and cerebellum. The initial response of the brain after rotationalhead injury involves brain edema after 24 h and an excitotoxic neuronal microenvironment in the first hour, which leads to extensive delayed neuronal cell death by apoptosis necrosis in the cerebral cortex, hippocampus and cerebellum.
  •  
24.
  • Gutierrez-Farewik, Elena M., et al. (författare)
  • Centre of mass motion during gait in persons with myelomeningocele
  • 2003
  • Ingår i: Gait & Posture. - 0966-6362 .- 1879-2219. ; 18:2, s. 37-46
  • Tidskriftsartikel (refereegranskat)abstract
    • The movement of the centre of mass in the vertical and lateral directions during gait in children with myelomeningocele was analyzed. The children were classified into five groups depending on the successive paresis of lower limb muscle groups and compared to a control group. In the groups with. dorsi- and plantarflexor weakness, the excursions increased and an anterior trend in the centre of mass was observed. In the groups with additional abductor paresis, the lateral excursion was highest and the vertical excursion low due to increased transverse and frontal motion and reduced sagittal motion. With further paresis of the hip extensors, the centre of mass was more posteriorly positioned due to compensatory trunk extension. Improved understanding of individual children's solutions to their muscle paresis can be obtained by visualizing the centre of mass relative to the pelvis. Centre of mass analyses in myelomeningocele offer an important complement to standard gait analysis.
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25.
  • Gutierrez-Farewik, Elena M., et al. (författare)
  • Characteristic gait kinematics in persons with lumbosacral myelomeningocele
  • 2003
  • Ingår i: Gait & Posture. - 0966-6362 .- 1879-2219. ; 18:3, s. 170-177
  • Tidskriftsartikel (refereegranskat)abstract
    • Thirty self-ambulatory children with mid-lumbar to low-sacral myelomeningocele who walked without aids and 21 control children were evaluated by three-dimensional gait analysis. Characteristic kinematic patterns and parameters in the trunk, pelvis, hip, knee and ankle were analyzed with respect to groups with successive weakness of the ankle plantarflexor, ankle dorsiflexor, hip abductor, hip extensor and knee flexor muscles. Extensive weakness of the plantarflexors resulted in kinematic alterations in the trunk, pelvis, hip and knee and in all three planes seen as knee flexion, anterior pelvic tilt and trunk and pelvic rotation. Additional extensive weakness of the dorsiflexors made little difference in the walking strategy. Large kinematic alterations in all planes were observed where there was a large extent of additional weakness of the hip abductor but strength remaining in the hip extensors. In this group, gait was characterized by large lateral sway of the trunk, rotation of the trunk and pelvis, pelvic hike and increased extension of the knees. In the group with total poresis hip extensors but yet some knee flexion, gait was similar to the previous group but there was less sagittal plane movement greates and posterior trunk tilt. Gait analysis provides an understanding of the compensatory strategies employed in these patients. Clinical management can be directed towards stabilizing the lower extremities and accommodating large upper body motion to preserve this method of self-ambulation even in children who have considerable hip extensor and abductor weakness.
  •  
26.
  • Gutierrez-Farewik, Elena M., et al. (författare)
  • Comparison and evaluation of two common methods to measure center of mass displacement in three dimensions during gait
  • 2006
  • Ingår i: Human Movement Science. - : Elsevier BV. - 0167-9457 .- 1872-7646. ; 25:2, s. 238-256
  • Tidskriftsartikel (refereegranskat)abstract
    • Center of mass displacement during gait has frequently been used as an indicator of gait efficiency or as a complement to standard gait analysis. With technological advances, measuring the center of mass as the centroid of a multi-segment system is practical and feasible, but must first be compared to the well-established Newtonian computation of double-integrating the ground reaction force. This study aims to verify that the kinematic centroid obtained from a commonly-used model (Vicon Peak (R) Plug-In-Gait) provides at least as reliable measurements of center of mass displacement as those obtained from the ground reaction forces. Gait data was collected for able-bodied children and children with myelomeningocele who use larger lateral center of mass excursions during gait. Reasonable agreement between methods was found in fore-aft and vertical directions, where the methods' excursions differed by an average of less than 10 mm in either direction, and the average RMS differences between methods' computed curves were 6 and 13 mm. Particularly good agreement was observed in the lateral direction, where the calculated excursions differed by an average of less than 2 mm and the RMS difference was 5 mm. Error analyses in computing the center of mass displacement from ground reaction forces were performed. A 5% deviation in mass estimation increased the computed vertical excursion twofold, and a 5% deviation in the integration constant of initial velocity increased the computed fore-aft excursions by 10%. The suitability of calculating center of mass displacement using ground reaction forces in a patient population is questioned. The kinematic centroid is susceptible to errors in segment parameters and marker placement, but results in plausible results that are at least within the range of doubt of the better-established ground reaction force integration, and are more useful when interpreting 3-D gait data.
  •  
27.
  • Gutierrez-Farewik, Elena M., et al. (författare)
  • Measuring seating pressure, area, and asymmetry in persons with spinal cord injury
  • 2004
  • Ingår i: European spine journal. - : Springer Science and Business Media LLC. - 0940-6719 .- 1432-0932. ; 13:4, s. 374-379
  • Tidskriftsartikel (refereegranskat)abstract
    • The goal of this study was to measure characteristics of seat loading in manual wheelchair users with complete spinal cord injury (SCI). Pressure distribution on the seating area of 25 adult males with SCI and eight non-injured adult males was measured in a relaxed and an upright posture on a standardized hard surface. Subjects with SCI were also tested in their wheelchairs. Maximum pressure, contact area, area of the highest pressure, and three asymmetry indices were compared. Subjects with SCI have higher pressure distributed over a smaller area, have a much smaller contact area, and distribute the loading more asymmetrically than non-injured subjects. Upright posture only corrects for some loading problems, while the wheelchair corrects for more loading parameters. Routine clinical seat loading evaluation may lead to improved chair and cushion selection for patients with SCI and may even alert clinicians to patients at high risk for complications due to high or unbalanced loads.
  •  
28.
  • Heintz, Sofia, et al. (författare)
  • Evaluation of load-sharing and load capacity in force-limited muscle systems
  • 2006
  • Ingår i: Computer Methods in Biomechanics and Biomedical Engineering. - 1025-5842 .- 1476-8259.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • This study had the objective to develop an algorithm for accurate force decomposition in a redundant musculoskeletal system. The hypothesis was that the calculated load-sharing is dependent on the optimality criterion adopted, but also on the magnitude of carried load. The developed algorithm emphasizes that several established optimization techniques can be unified, by identifying and separating the underlying optimization functions and the numerical methods to solve the resulting system. A numerically efficient and easily adaptable solution method is thereby created. In addition, individual capacity values are introduced for the muscles, allowing the evaluation of a magnitude-dependent load-sharing, and a load carrying capacity of the whole system. By modularizing the optimization method, the algorithm can be used as part of larger simulation systems. To illustrate the possibilities of the algorithm, a model of the upper limb is used in a set of demonstrative examples. The results from the examples show how the interactions between synergistic muscles is predicted in different configurations, and at different load levels.
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29.
  • Heintz, Sofia, 1972- (författare)
  • Muscular forces from static optimization
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • At every joint there is a redundant set of muscle activated during movement or loading of the system. Optimization techniques are needed to evaluate individual forces in every muscle. The objective in this thesis was to use static optimization techniques to calculate individual muscle forces in the human extremities. A cost function based on a performance criterion of the involved muscular forces was set to be minimized together with constraints on the muscle forces, restraining negative and excessive values. Load-sharing, load capacity and optimal forces of a system can be evaluated, based on a description of the muscle architectural properties, such as moment arm, physiological cross-sectional area, and peak isometric force. The upper and lower extremities were modelled in two separate studies. The upper extremity was modelled as a two link-segment with fixed configurations. Load-sharing properties in a simplified model were analyzed. In a more complex model of the elbow and shoulder joint system of muscular forces, the overall total loading capacity was evaluated. A lower limb model was then used and optimal forces during gait were evaluated. Gait analysis was performed with simultaneous electromyography (EMG). Gait kinematics and kinetics were used in the static optimization to evaluate of optimal individual muscle forces. EMG recordings measure muscle activation. The raw EMG data was processed and a linear envelope of the signal was used to view the activation profile. A method described as the EMG-to-force method which scales and transforms subject specific EMG data is used to compare the evaluated optimal forces. Reasonably good correlation between calculated muscle forces from static optimization and EMG profiles was shown. Also, the possibility to view load-sharing properties of a musculoskeletal system demonstrate a promising complement to traditional motion analysis techniques. However, validation of the accurate muscular forces are needed but not possible. Future work is focused on adding more accurate settings in the muscle architectural properties such as moment arms and physiological cross-sectional areas. Further perspectives with this mathematic modelling technique include analyzing pathological movement, such as cerebral palsy and rheumatoid arthritis where muscular weakness, pain and joint deformities are common. In these, better understanding of muscular action and function are needed for better treatment.
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30.
  • Heintz, Sofia, et al. (författare)
  • Static optimization of muscle forces during gait in comparison to EMG-to-force processing approach
  • 2007
  • Ingår i: Gait & Posture. - : Elsevier BV. - 0966-6362 .- 1879-2219. ; 26:2, s. 279-288
  • Tidskriftsartikel (refereegranskat)abstract
    • Individual muscle forces evaluated from experimental motion analysis may be useful in mathematical simulation, but require additional musculoskeletal and mathematical modelling. A numerical method of static optimization was used in this study to evaluate muscular forces during gait. The numerical algorithm used was built on the basis of traditional optimization techniques, i.e., constrained minimization technique using the Lagrange multiplier method to solve for constraints. Measuring exact muscle forces during gait analysis is not currently possible. The developed optimization method calculates optimal forces during gait, given a specific performance criterion, using kinematics and kinetics from gait analysis together with muscle architectural data. Experimental methods to validate mathematical methods to calculate forces are limited. Electromyography (EMG) is frequently used as a tool to determine muscle activation in experimental studies on human motion. A method of estimating force from the EMG signal, the EMG-to-force approach, was recently developed by Bogey et al. [Bogey RA, Perry J, Gitter AJ. An EMG-to-force processing approach for determining ankle muscle forcs during normal human gait. IEEE Trans Neural Syst Rehabil Eng 2005;13:302-10] and is based on normalization of activation during a maximum voluntary contraction to documented maximal muscle strength. This method was adapted in this study as a tool with which to compare static optimization during a gait cycle. Muscle forces from static optimization and from EMG-to-force muscle forces show reasonably good correlation in the plantarflexor and dorsiflexor muscles, but less correlation in the knee flexor and extensor muscles. Additional comparison of the mathematical muscle forces from static optimization to documented averaged EMG data reveals good overall correlation to patterns of evaluated muscular activation. This indicates that on an individual level, muscular force patterns from mathematical models can arguably be more accurate than from those obtained from surface EMG during gait, though magnitude must still be validated.
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31.
  • Kizyte, Asta, 1993- (författare)
  • High-Density Electromyography-Based Methods for Joint Torque Prediction and Motor Unit Behavior Observation
  • 2023
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Electromyography (EMG) is a technique that measures the electrical activity of muscles. It reflects muscle activation and provides an interface to the central nervous system at the level of the muscle or individual motor units, which helps us understand the mechanisms of muscle force production, control, and coordination. EMG can also be used to detect changes in muscle activity caused by pathology, making it a valuable tool for research, diagnosis, and rehabilitation. One of the latest advancements in EMG technology is high-density EMG (HD-EMG). HD-EMG measures multiple spatially separated samples of muscle activation. This additional spatial information in HD-EMG offers new possibilities for the prediction of joint torques and the ability to look into individual motor units by decomposing the signals using blind source separation methods. This thesis presents two studies that explore the use of HD-EMG methods for joint torque estimation and the observation of motor unit behavior. In the first paper, we presented a detailed investigation of the effects of different EMG and kinematic inputs on the accuracy and robustness of ankle joint torque prediction using support vector regression. To evaluate the robustness, we analyzed the results in three cases (intra-session, inter-subject, and inter-session) and two movement categories (isometric contraction and dynamic movement). We found that HD-EMG-derived inputs improve the accuracy and robustness of torque prediction of the isometric contractions. However, in dynamic movements, good prediction results could only be achieved by including additional kinematic features (ankle joint position and angular velocity), and the type of EMG input did not strongly influence the results.In the second paper, we investigated the changes in motor unit behavior of the ankle plantar flexor (soleus) and dorsiflexor (tibialis anterior) caused by spinal cord injury (SCI). We computed torque, EMG, and motor unit parameters during volitional sub-maximal voluntary contractions for the SCI group and compared them to a non-injured control cohort. We found that participants in both groups could maintain the prescribed torque with similar variability. However, the SCI group required higher muscle activation levels (normalized to maximum) to achieve the same level of relative torque compared to the control group. The SCI group had lower intramuscular coherence in the alpha frequency band than the control group, indicating altered neural synchronization at the sub-cortical level. The soleus motor unit firing patterns were more variable post-SCI than in the control group. In addition, at high torque levels (50% of personal maximum), both muscle's motor units were recruited and de-recruited at lower torques, and motor units fired at lower rates in the tibialis anterior muscle in persons with SCI, indicating altered force gradation strategies after the injury.The studies presented in this thesis demonstrated that HD-EMG is suitable for robust isometric ankle joint torque prediction, which has potential in applications such as robot-assisted rehabilitation and robotic gait assistive technology. In particular, the robustness and accuracy of HD-EMG-based predictions are essential for improved estimation of the joint torque that can then be used in the human-in-the-loop control scheme. In addition, HD-EMG decomposition enables a non-invasive way to observe the motor unit behavior in vivo in persons with neuromusculoskeletal disorders, which can enhance the understanding of the underlying neurophysiological mechanisms of motor impairments. The insights provided by such HD-EMG analysis in the future may be beneficial for developing targeted interventions and personalized therapies.
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32.
  • Kizyte, Asta, 1993-, et al. (författare)
  • Neuromuscular adaptations in ankle plantar flexor and dorsiflexor in persons with spinal cord injury
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Objective: Spinal cord injury (SCI) could lead to sensory-motor impairment of varying degree. After the injury, multiple neurophysiological changes occur, altering the neural motor control strategies. This study aims to assess the neuromuscular adaptations in the ankle plantar flexor and dorsiflexor muscles after the SCI by examining the electromyography (EMG) and motor unit parameters during sub-maximal voluntary isometric contractions and comparing these parameters to a control cohort. Methods: High-density EMG (HD-EMG) signals of tibialis anterior and soleus were recorded simultaneously with ankle joint torque during repeated sub-maximal (20% and 50% of the maximal torque) isometric voluntary contractions. Torque parameters such as normalized torque and coefficient of variation of torque during sustained contraction, EMG parameters such as amplitude and intramuscular coherence, as well as motor unit parameters such as motor unit discharge rates, recruitment thresholds, and coefficient of variation of the inter-spike intervals, were analyzed within the SCI and control groups. Results: We found that the SCI group, on average, had significantly weaker plantar flexor but not dorsiflexor muscles than the control group. Despite the increased variation of soleus motor unit inter-spike intervals post-SCI, both groups maintained constant sub-maximal torques with similar variability. However, the SCI group required up to 40.2% higher normalized EMG amplitudes to achieve the same torque level as the control group. Additionally, intramuscular coherence was found to be lower (up to 38.1% in TA and 34.6% in SOL) in the SCI group compared to the control group in the alpha frequency band during sustained sub-maximal isometric contractions. At higher force levels (50% MVC), motor units were recruited and de-recruited at lower thresholds in both muscles and fired at lower rates in the tibialis anterior muscle post-SCI. Conclusion: Through the analysis of these parameters, we observed altered force production and modulation strategies post-SCI. The observed combination of the motor unit and EMG parameter changes may indicate reduced common neural drive within the muscle and a possible shift towards larger motor units and in both TA and SOL muscles. Significance: The results of this study contribute to the knowledge of the neurophysiological modifications in the ankle dorsiflexors and plantar flexors following the SCI, which may aid future research on SCI rehabilitation.
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33.
  • Klets, Olesya, et al. (författare)
  • Comparison between a subject-specific and a scaled generic musculoskeletal model of the lower extremities in a subject with unilateral cerebral palsy
  • 2011
  • Ingår i: Clinical Biomechanics. - 0268-0033 .- 1879-1271.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The purpose of this paper was to develop methods to build a subject-specific musculoskeletal model of the lower extremities based on MRIs of a subject with unilateral CP, and to determine whether a scaled generic musculoskeletal model is accurate enough to characterize MTLs and MALs of 70 muscles in both lower limbs during gait in a subject with unilateral cerebral palsy. We found, that the generic models produced accurate values for changes in MTL during gait for almost all muscles, except adductor longus, adductor magnus, adductor brevis, quadratus femoris, pectineus, extensor digitorum longus, soleus, lateral gastrocnemius, and medial gastrocnemius. MALs computed from the scaled generic model, however, differed considerably from those computed from the subject-specific model. Upon comparison of hip, knee and ankle MALs in affected and non-affected sides of the lower extremities, the scaled generic model generally failed to identify level arm dysfunction in the subject with unilateral CP
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34.
  •  
35.
  • Klets, Olesya, 1985- (författare)
  • Subject-specific musculoskeletal modeling of the lower extremities in persons with unilateral cerebral palsy
  • 2011
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The computational musculoskeletal models that are used to study muscle moment-generating capacities of persons with movement disorders and planning treatment options must be accurate, and take into account the inter-individual variability of musculoskeletal geometry. In Paper I the methods of creating the subject-specific musculoskeletal model of the lower extremities from magnetic resonance images (MRIs) were developed. The subject-specific model was used to analyze hip, knee and ankle muscle moment arms (MALs) and muscle-tendon lengths (MTLs) during gait in a subject with unilateral cerebral palsy (CP), and to evaluate the accuracy of widespread and commonly-used scaled generic model. It was found that the scaled generic model delivered accurate values for changes in MTLs in most muscles. However, the scaled generic and the subject-specific lower extremity musculoskeletal models showed substantial differences in MALs calculated during gait. In Paper II subject-specific musculoskeletal models of nine subjects with unilateral CP were created to study muscles volumes, MTLs and MALs; and to examine the accuracy of MALs calculated by the scaled generic models. It was shown that the scaled generic model significantly underestimated hip MALs discrepancies between the affected and the non-affected sides of the lower extremities. However, it significantly overestimated hip adduction/abduction of gluteus maximus, gluteus medius, gluteus minimus, tensor fascia latae and biceps femoris long head; and hip flexion of adductor longus and rectus femoris in the affected and the non-affected sides. It was also found that muscle volumes and hip abduction MALs in gluteus medius and gluteus minimus, hip flexion MALs in iliacus and hip rotation in gluteus maximus were smaller in the affected side of lower extremities. MTLs in the affected and the non-affected sides throughout the range of hip motion were similar. This thesis suggests the need for the subject-specific musculoskeletal models that can account for variability of muscle attachments and musculoskeletal geometry of persons with movement disorders. Based on inaccuracies of the scaled generic model reported here, the generic models that are used to guide treatment decisions must be tested, and interpreted with care.
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36.
  • Krishnan, Rakesh, et al. (författare)
  • Reliably Segmenting Motion Reversals of a Rigid-IMU Cluster Using Screw-Based Invariants
  • 2018
  • Ingår i: 2018 IEEE-RAS 18TH INTERNATIONAL CONFERENCE ON HUMANOID ROBOTS (HUMANOIDS). ; , s. 88-95
  • Konferensbidrag (refereegranskat)abstract
    • Human-robot interaction (HRI) is moving towards the human-robot synchronization challenge. In robots like exoskeletons, this challenge translates to the reliable motion segmentation problem using wearable devices. Therefore, our paper explores the possibility of segmenting the motion reversals of a rigid-IMU cluster using screw-based invariants. Moreover, we evaluate the reliability of this framework with regard to the sensor placement, speed and type of motion. Overall, our results show that the screw-based invariants can reliably segment the motion reversals of a rigid-IMU cluster.
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37.
  • Lidbeck, Cecilia M., et al. (författare)
  • Postural Orientation During Standing in Children With Bilateral Cerebral Palsy
  • 2014
  • Ingår i: Pediatric Physical Therapy. - 0898-5669 .- 1538-005X. ; 26:2, s. 223-229
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: To investigate postural orientation and maintenance of joint position during standing in children with bilateral spastic cerebral palsy (BSCP). Methods: Standing was examined with 3-D motion analysis in 26 children with BSCP, and 19 children typically developing (TD). Two groups of children with cerebral palsy (CP) were analyzed: 15 who were able to maintain standing without support and 11 who needed support. Results: Children with CP stood with more flexion than children TD. In the CP groups, children standing without support stood more asymmetrically with less hip and knee flexion and less movement than those who required support. Conclusion: Children with CP had varying abilities to stand and maintain standing posture with or without support. Both CP groups stood with more flexion than their potential passive joint angle, more obvious in children requiring support. Investigations on how muscle strength and spatial perception influence posture remains to be explored.
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38.
  • Lidbeck, Cecilia, et al. (författare)
  • The role of visual stimuli on standing posture in children with bilateral cerebral palsy
  • 2016
  • Ingår i: BMC Neurology. - : BioMed Central. - 1471-2377. ; 16:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: In children with bilateral cerebral palsy (CP) maintaining a standing position can be difficult. The fundamental motor task of standing independently is achieved by an interaction between the visual, somatosensory, and vestibular systems. In CP, the motor disorders are commonly accompanied by sensory and perceptual disturbances. Our aims were to examine the influence of visual stimuli on standing posture in relation to standing ability. Methods: Three dimensional motion analysis with surface electromyography was recorded to describe body position, body movement, and muscle activity during three standing tasks: in a self-selected position, while blindfolded, and during an attention-demanding task. Participants were twenty-seven typically-developing (TD) children and 36 children with bilateral CP, of which 17 required support for standing (CP-SwS) and 19 stood without support (CP-SwoS). Results: All children with CP stood with a more flexed body position than the TD children, even more pronounced in the children in CP-SwS. While blindfolded, the CP-SwS group further flexed their hips and knees, and increased muscle activity in knee extensors. In contrast, the children in CP-SwoS maintained the same body position but increased calf muscle activity. During the attention-demanding task, the children in CP-SwoS stood with more still head and knee positions and with less muscle activity. Conclusions: Visual input was important for children with CP to maintain a standing position. Without visual input the children who required support dropped into a further crouched position. The somatosensory and vestibular systems alone could not provide enough information about the body position in space without visual cues as a reference frame. In the children who stood without support, an intensified visual stimulus enhanced the ability to maintain a quiet standing position. It may be that impairments in the sensory systems are major contributors to the difficulties to stand erect in children with CP.
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39.
  • Liu, Yixing, et al. (författare)
  • A method of detecting human movement intentions in real environments
  • 2023
  • Ingår i: 2023 international conference on rehabilitation robotics, ICORR. - : Institute of Electrical and Electronics Engineers (IEEE).
  • Konferensbidrag (refereegranskat)abstract
    • Accurate and timely movement intention detection can facilitate exoskeleton control during transitions between different locomotion modes. Detecting movement intentions in real environments remains a challenge due to unavoidable environmental uncertainties. False movement intention detection may also induce risks of falling and general danger for exoskeleton users. To this end, in this study, we developed a method for detecting human movement intentions in real environments. The proposed method is capable of online self-correcting by implementing a decision fusion layer. Gaze data from an eye tracker and inertial measurement unit (IMU) signals were fused at the feature extraction level and used to predict movement intentions using 2 different methods. Images from the scene camera embedded on the eye tracker were used to identify terrains using a convolutional neural network. The decision fusion was made based on the predicted movement intentions and identified terrains. Four able-bodied participants wearing the eye tracker and 7 IMU sensors took part in the experiments to complete the tasks of level ground walking, ramp ascending, ramp descending, stairs ascending, and stair descending. The recorded experimental data were used to test the feasibility of the proposed method. An overall accuracy of 93.4% was achieved when both feature fusion and decision fusion were used. Fusing gaze data with IMU signals improved the prediction accuracy.
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40.
  • Liu, Yixing, et al. (författare)
  • A Muscle Synergy-Inspired Method of Detecting Human Movement Intentions Based on Wearable Sensor Fusion
  • 2021
  • Ingår i: IEEE transactions on neural systems and rehabilitation engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 1534-4320 .- 1558-0210. ; 29, s. 1089-1098
  • Tidskriftsartikel (refereegranskat)abstract
    • Detecting human movement intentions is fundamental to neural control of robotic exoskeletons, as it is essential for achieving seamless transitions between different locomotion modes. In this study, we enhanced a muscle synergy-inspired method of locomotion mode identification by fusing the electromyography data with two types of data from wearable sensors (inertial measurement units), namely linear acceleration and angular velocity. From the finite state machine perspective, the enhanced method was used to systematically identify 2 static modes, 7 dynamic modes, and 27 transitions among them. In addition to the five broadly studied modes (level ground walking, ramps ascent/descent, stairs ascent/descent), we identified the transition between different walking speeds and modes of ramp walking at different inclination angles. Seven combinations of sensor fusion were conducted, on experimental data from 8 able-bodied adult subjects, and their classification accuracy and prediction time were compared. Prediction based on a fusion of electromyography and gyroscope (angular velocity) data predicted transitions earlier and with higher accuracy. All transitions and modes were identified with a total average classification accuracy of 94.5% with fused sensor data. For nearly all transitions, we were able to predict the next locomotion mode 300-500ms prior to the step into that mode.
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41.
  • Liu, Yixing, et al. (författare)
  • Joint Kinematics, Kinetics and Muscle Synergy Patterns During Transitions Between Locomotion Modes
  • 2023
  • Ingår i: IEEE Transactions on Biomedical Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9294 .- 1558-2531. ; 70:3, s. 1062-1071
  • Tidskriftsartikel (refereegranskat)abstract
    • There is an increasing demand for accurately predicting human movement intentions. To be effective, predictions must be performed as early as possible in the preceding step, though precisely how early has been studied relatively little; how and when a person's movement patterns in a transition step deviate from those in the preceding step must be clearly defined. In this study, we collected motion kinematics, kinetics and electromyography data from 9 able-bodied participants during 7 locomotion modes. Twelve types of steps between the 7 locomotion modes were studied, including 5 continuous steps (taking another step in the same locomotion mode) and 7 transitions steps (taking a step from one locomotion mode into another). For each joint degree of freedom, joint angles, angular velocities, moments, and moment rates were compared between continuous steps and transition steps, and the relative timing during the transition step at which these parameters diverged from those of a continuous step, which we refer to as transition starting times, were identified using multiple analyses of variance. Muscle synergies were also extracted for each step, and we studied in which locomotion modes these synergies were common (task-shared) and in which modes they were specific (task-specific). The transition starting times varied among different transitions and joint degrees of freedom. Most transitions started in the swing phase of the transition step. These findings can be applied to determine the critical timing at which a powered assistive device must adapt its control to enable safe and comfortable support to a user.
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42.
  • Liu, Yixing, et al. (författare)
  • Weight Distribution of a Knee Exoskeleton Influences Muscle Activities During Movements
  • 2021
  • Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 9, s. 91614-91624
  • Tidskriftsartikel (refereegranskat)abstract
    • Lower extremity powered exoskeletons help people with movement disorders to perform daily activities and are used increasingly in gait retraining and rehabilitation. Studies of powered exoskeletons often focus on technological aspects such as actuators, control methods, energy and effects on gait. Limited research has been conducted on how different mechanical design parameters can affect the user. In this paper, we study the effects of weight distributions of knee exoskeleton components on simulated muscle activities during three functional movements. Four knee exoskeleton CAD models were developed based on actual motor and gear reducer products. Different placements of the motor and gearbox resulted in different weight distributions. One unilateral knee exoskeleton prototype was fabricated and tested on 5 healthy subjects. Simulation results were compared to observed electromyography signals. Muscle activities varied among weight distributions and movements, wherein no one physical design was optimal for all movements. We describe how a powered exoskeleton's core components can be expected to affect a user's ability and performance. Exoskeleton physical design should ideally take the user's activity goals and ability into consideration.
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43.
  • Liu, Yi-Xing, 1993- (författare)
  • Facilitating Exoskeletons in Daily Use : Simulations and Predictions for Design and Control
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lower limb exoskeletons have been extensively developed over the last several decades for people with and without movement disorders. Although lower limb exoskeletons have been shown to provide effective assistance to improve gait and reduce metabolic cost during movements, they are often heavy, bulky and uncomfortable.  Many studies with exoskeletons are limited to indoor environments and to overground or treadmill walking at a constant speed, whereas one's activities in daily life include several types of locomotion over various terrains. In order to provide adequate control in many locomotion types and in the transitions between them, an exoskeleton requires sensors to accurately detect the user's movement capacity and intentions, which may require a great number of wearable sensors. For these reasons, feasible exoskeleton use in daily life remains a challenge. The studies in this thesis are aimed at addressing some of these limitations.The overall objectives of this thesis are to study movement biomechanics in different locomotion modes, to develop useful methods to study the interaction between a wearable exoskeleton and its user, and to develop methods that detect a person's movement ability and intentions with minimal sensor requirements. The aims of the first two studies were to create a simulation of an exoskeleton and its user and to study how different exoskeleton parameters affect the user; specifically, to study the influence of a knee exoskeleton's different weight distributions and assistive strategies on the user's required muscular effort and on the interaction forces. The aim of the third and fourth studies was to study the biomechanics and biosignals during different locomotion modes and the transitions between them, such as walking and stair climbing, and to use these signals to detect as early as possible a person's movement intentions to transition from one mode to another. The aim of the fifth study was to accurately predict, with as few wearable sensors as possible, a person's generated knee joint moment during walking.The methods used in this thesis include musculoskeletal modeling and simulation, experimental motion capture of able-bodied participants, physical prototyping of a knee exoskeleton, and off-line prediction algorithms based on captured motion data, using fundamental concepts from muscle synergy and from recurrent neural networks.The main findings in the first two studies are that the influence of a knee exoskeleton's weight distribution on muscle activities was movement-dependent; the external load in various exoskeleton configurations led to an additional required effort in some movements but not in all, suggesting that an exoskeleton's physical design should be aligned with the intended user's movement goals. Further main findings were that simulations of an exoskeleton's assistive strategies and the resulting muscular efforts of the user can assist in and possibly speed up the prototyping process. The focus in the third and fourth studies is on movement biomechanics and biosignals in various modes of locomotion and in the transitions between them. The main findings in these studies are that the computational methods we propose based on wearable sensor signals could accurately detect a person's movement intentions to transition between locomotion modes during the step preceding the transition. This finding has important potential in the design and execution of exoskeleton control. Finally, the main findings in the fifth study are that an accurate prediction of a person's knee joint moments could be performed with as few as four electromyography sensors.  Application of these findings can have important potential in facilitating more feasibility and compliance in exoskeleton use in realistic contexts in the future.
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44.
  • Liu, Yi-Xing, 1993-, et al. (författare)
  • Joint kinematics, kinetics and muscle synergy patterns during transitions between locomotion modes
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • There is an increasing demand for accurately predicting a person's movement intentions, for instance, for robotic exoskeletons to achieve seamless transitions between locomotion modes. To this end, many methods have been reported to identify locomotion modes and the transitions between them with high classification accuracy. To be effective, predictions must be performed as early as possible in the preceding step, though precisely how early has been studied relatively little; how and when a persons' movement patterns in a transition step deviate from those in the preceding step must be clearly defined. In this study, we collected motion kinematics, kinetics and electromyography data from 9 able-bodied subjects during 7 locomotion modes and transitions between them, and computed joint angles and moments in the hip in frontal and sagittal planes and at the knee and ankle in the sagittal plane. Locomotion modes included level ground walking, ramp and stair ascent and descent, stepping over an obstacle and standing still. Twelve types of steps between the 7 locomotion modes were studied, including 5 continuous steps (taking another step in the same locomotion mode) and 7 transitions (taking a step from one locomotion mode into another). For each joint degree of freedom, four dependent time-series variables, namely joint angles, angular velocities, joint moments, and joint moment rates, as functions of percent gait cycle, were compared between continuous steps and transition steps, and the relative timing during the transition step at which these parameters diverged from those of a continuous step, which we refer to as transition starting time, were identified using multiple analyses of variance. We also compared these parameters during each transition to those in a continuous step in the mode after the transition, to determine whether there are period in the transition step during which kinematics and kinetics are unique.  Muscle synergies were also extracted for each continuous and transition step, and we studied in which locomotion modes these synergies were common (task-shared) and in which modes they were specific (task-specific). The transition starting times varied among different transitions and joint degrees of freedom. Most transitions, such as from walking to standing still and from walking to ramp ascent, started in the swing phase of the transition step, though the transition from walking to stepping over an obstacle began earlier, i.e. during mid- to late stance phase. We identified 3-4 task-shared muscle synergies and 1-2 task-specific muscle synergies between each pair of transitions. These findings can be applicability in determining the critical timing at which a powered assistive device must adapt its control to enable safe and comfortable support to a user.
  •  
45.
  • Liu, Yi-Xing, et al. (författare)
  • Muscle synergies enable accurate joint moment prediction using few electromyography sensors
  • 2021
  • Ingår i: 2021 IEEE International Conference on Intelligent Robots and Systems (IROS). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 5090-5097
  • Konferensbidrag (refereegranskat)abstract
    • There is an increasing demand for accurate prediction of joint moments using wearable sensors for robotic exoskeletons to achieve precise control and for rehabilitation care to remotely monitor users’ condition. In this study, we used electromyography (EMG) signals to first identify muscle synergies, then used them to train of a long short-term memory network to predict knee joint moments during walking. Kinematics, ground reaction forces, and EMG from 10 muscles on the right limb were collected from 6 able-bodied subjects during normal gait. Between 4 and 6 muscle synergies were extracted from the EMG signals, generating two outputs - the muscle synergies weight matrix and the time-dependent muscle synergies action signals. The muscle synergies action signals and measured knee joint moments from inverse dynamics were then used as inputs to train the joint moment prediction model using a long short-term memory network. For testing, between4 and 7 EMG signals were used to estimate the muscle synergies action signals with the extracted muscle synergies weights matrix. The estimated muscle synergies action signals were then used to predict knee joint moments. Knee joint moments were also predicted directly from all 10 EMGs, then from 4-7EMG signals using another long short-term memory network. Prediction accuracy from the synergies-trained network vs. the EMG-trained network were compared, using the same number of EMG signals in each. Prediction error with respect to moments measured via inverse dynamics was computed for both networks. Knee moments predicted with as few as 4 EMGswas at least as accurate as moments predicted from all 10 EMGswhen muscle synergies were exploited. Predicted knee moments from muscle synergies achieved an average of 4.63% root mean square error from 4 EMG signals, which was lower than error when predicted directly from 4 EMG signals (5.63%).
  •  
46.
  • Luis, Israel, et al. (författare)
  • Evaluation of musculoskeletal models, scaling methods, and performance criteria for estimating muscle excitations and fiber lengths across walking speeds
  • 2022
  • Ingår i: Frontiers in Bioengineering and Biotechnology. - : Frontiers Media SA. - 2296-4185. ; 10
  • Tidskriftsartikel (refereegranskat)abstract
    • Muscle-driven simulations have been widely adopted to study muscle-tendon behavior; several generic musculoskeletal models have been developed, and their biofidelity improved based on available experimental data and computational feasibility. It is, however, not clear which, if any, of these models accurately estimate muscle-tendon dynamics over a range of walking speeds. In addition, the interaction between model selection, performance criteria to solve muscle redundancy, and approaches for scaling muscle-tendon properties remain unclear. This study aims to compare estimated muscle excitations and muscle fiber lengths, qualitatively and quantitatively, from several model combinations to experimental observations. We tested three generic models proposed by Hamner et al., Rajagopal et al., and Lai-Arnold et al. in combination with performance criteria based on minimization of muscle effort to the power of 2, 3, 5, and 10, and four approaches to scale the muscle-tendon unit properties of maximum isometric force, optimal fiber length, and tendon slack length. We collected motion analysis and electromyography data in eight able-bodied subjects walking at seven speeds and compared agreement between estimated/modelled muscle excitations and observed muscle excitations from electromyography and computed normalized fiber lengths to values reported in the literature. We found that best agreement in on/off timing in vastus lateralis, vastus medialis, tibialis anterior, gastrocnemius lateralis, gastrocnemius medialis, and soleus was estimated with minimum squared muscle effort than to higher exponents, regardless of model and scaling approach. Also, minimum squared or cubed muscle effort with only a subset of muscle-tendon unit scaling approaches produced the best time-series agreement and best estimates of the increment of muscle excitation magnitude across walking speeds. There were discrepancies in estimated fiber lengths and muscle excitations among the models, with the largest discrepancy in the Hamner et al. model. The model proposed by Lai-Arnold et al. best estimated muscle excitation estimates overall, but failed to estimate realistic muscle fiber lengths, which were better estimated with the model proposed by Rajagopal et al. No single model combination estimated the most accurate muscle excitations for all muscles; commonly observed disagreements include onset delay, underestimated co-activation, and failure to estimate muscle excitation increments across walking speeds.
  •  
47.
  • Luis, Israel, et al. (författare)
  • Experiment-guided tuning of muscle fiber lengths and passive forces
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Musculoskeletal simulations can provide insights into the roles of muscles and tendons during motion. Accuratedescriptions of musculoskeletal parameters increase our confidence in the estimations of dynamics andenergetics of muscles, tendons, and joints. In this study, we present a computational tool to tune muscle-tendonparameters based on prior experimental observations in literature and evaluate their influence on estimatedmuscle excitations. From a scaled generic musculoskeletal model, we tuned optimal fiber length, tendon slacklength, and tendon stiffness to match reported digitalized images from ultrasound, and muscle passive curvesto match reported in vivo experimental angle-moment relationship. Our proposed workflow improved theestimation of muscle fiber lengths in the ankle plantarflexors compared to linearly scaling optimal fiber lengthsand tendon slack lengths. Also, with tuned muscle-tendon parameters, estimated the on/off timing of nearly allmuscles’ excitations in the model compared to reported values in literature. Our workflow customizes muscletendonparameters easily and quickly. The computational toolbox is freely available online.Keywords
  •  
48.
  • Luis, Israel, et al. (författare)
  • Experiment-guided tuning of muscle–tendon parameters to estimate muscle fiber lengths and passive forces
  • 2024
  • Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The workflow to simulate motion with recorded data usually starts with selecting a generic musculoskeletal model and scaling it to represent subject-specific characteristics. Simulating muscle dynamics with muscle–tendon parameters computed from existing scaling methods in literature, however, yields some inconsistencies compared to measurable outcomes. For instance, simulating fiber lengths and muscle excitations during walking with linearly scaled parameters does not resemble established patterns in the literature. This study presents a tool that leverages reported in vivo experimental observations to tune muscle–tendon parameters and evaluates their influence in estimating muscle excitations and metabolic costs during walking. From a scaled generic musculoskeletal model, we tuned optimal fiber length, tendon slack length, and tendon stiffness to match reported fiber lengths from ultrasound imaging and muscle passive force–length relationships to match reported in vivo joint moment–angle relationships. With tuned parameters, muscle contracted more isometrically, and soleus’s operating range was better estimated than with linearly scaled parameters. Also, with tuned parameters, on/off timing of nearly all muscles’ excitations in the model agreed with reported electromyographic signals, and metabolic rate trajectories varied significantly throughout the gait cycle compared to linearly scaled parameters. Our tool, freely available online, can customize muscle–tendon parameters easily and be adapted to incorporate more experimental data.
  •  
49.
  • Luis, Israel, et al. (författare)
  • Insights into muscle metabolic energetics: Modelling muscle-tendon mechanics and metabolicrates during walking across speeds
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The metabolic energy rate of individual muscles is impossible to measure without invasive procedures. Priorstudies have produced models to predict metabolic rates based on experimental observations of isolated musclecontraction from various species. Such models can provide reliable predictions of metabolic rates in humans ifmuscle properties and control are accurately modelled. This study aimed to examine how muscle-tendon modelcalibration and metabolic energy models influenced estimation of muscle-tendon states and time-seriesmetabolic rates, to evaluate the agreement with empirical data, and to provide predictions of the metabolic rateof muscle groups and gait phases across walking speeds. Three-dimensional musculoskeletal simulations withprescribed kinematics and dynamics were performed. An optimal control formulation was used to computemuscle-tendon states with four levels of individualization, ranging from a scaled generic model and musclecontrols based on minimal activations, to calibration of passive muscle forces, personalization of Achilles andquadriceps tendon stiffnesses, to finally informing muscle controls with electromyography. We computedmetabolic rates based on existing models. Simulations with calibrated passive forces and personalized tendonstiffness most accurately estimate muscle excitations and fiber lengths. Interestingly, the inclusion ofelectromyography did not improve our estimates. The whole-body average metabolic cost was better estimatedusing Bhargava et al. 2004 and Umberger 2010 models. We estimated metabolic rate peaks near early stance,pre-swing, and initial swing at all walking speeds. Plantarflexors accounted for the highest cost among musclegroups at the preferred speed and was similar to the cost of hip adductors and abductors combined. Also, theswing phase accounted for slightly more than one-quarter of the total cost in a gait cycle, and its relative costdecreased with walking speed. Our prediction might inform the design of assistive devices and rehabilitationtreatment. The code and experimental data are available online.
  •  
50.
  • Luis, Israel, et al. (författare)
  • Springs vs. motors: Ideal assistance in the lower limbs during walking at different speeds
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Recent years have witnessed break throughs in assistive exoskeletons; both passive and active devices have reduced metabolic costs near preferred walking speed by assisting muscle actions. Metabolic reductions at multiple speeds should thus also be attainable. Musculo skeletal simulation can potentially predict the interaction between assistive moments, muscle-tendon mechanics, and walking energetics. In this study, we simulated devices’ optimal assistive moments based on minimal muscle activations during walking with prescribed kinematics and dynamics. We used a generic musculo  skeletal model with calibrated muscle-tendon parameters and computed metabolic rates from muscle actions. We then simulated walking across multiple speeds and with two ideal actuation modes – motor-based and spring-based – to assist ankle plantar flexion,knee extension, hip flexion, and hip abduction and compared computed metabolic rates. We found that both actuation modes considerably reduced physiological joint moments but did not always reduce metabolic rates. Compared to unassisted conditions, motor-based ankle plantar flexion and hip flexion assistance reduced metabolic rates, and this effect was more pronounced as walking speed increased. Spring-based hip flexion and abduction assistance increased metabolic rates at some walking speeds despite a moderate decrease in some muscle activations. Both modes of knee extension assistance reduced metabolic rates to a small extent, eventhough the actuation contributed with practically the entire net knee extension moment during stance. Motorbased hip abduction assistance reduced metabolic rates more than spring-based assistance, though this reduction was relatively small. Future work should experimentally validate the effects of assistive moments andrefine modeling assumptions accordingly. Our computational workflow is freely available online.
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