| 1. |
- Holmberg, L. Joakim, 1971-
(författare)
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Musculoskeletal Biomechanics in Cross-country Skiing
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Why copy the best athletes? When you finally learn their technique, they may have already moved on. Using muscluloskeletal biomechanics you might be able to add the "know-why" so that you can lead, instead of being left in the swells.This dissertation presents the theoretical framework of musculoskeletal modeling using inverse dynamics with static optimization. It explores some of the possibilities and limitations of musculoskeletal biomechanics in cross-country skiing, especially double-poling. The basic path of the implementation is shown and discussed, e.g. the issue of muscle model choice. From that discussion it is concluded that muscle contraction dynamics is needed to estimate individual muscle function in double-poling. Several computer simulation models, using The Anybody Modeling System™, have been created to study different cross-country skiing applications. One of the applied studies showed that the musculoskeletal system is not a collection of discrete uncoupled parts because kinematic differences in the lower leg region caused kinetic differences in the other end of the body. An implication of the results is that the kinematics and kinetics of the whole body probably are important when studying skill and performance in sports. Another one of the applied studies showed how leg utilisation may affect skiing efficiency and performance in double-poling ergometry. Skiing efficiency was defined as skiing work divided by metabolic muscle work, performance was defined as forward impulse. A higher utilization of the lower-body increased the performance, but decreased the skiing efficiency. The results display the potential of musculoskeletal biomechanics for skiing efficiency estimations. The subject of muscle decomposition is also studied. It is shown both analytically and with numerical simulations that muscle force estimates may be affected by muscle decomposition depending on the muscle recruitment criteria. Moreover, it is shown that proper choices of force normalization factors may overcome this issue. Such factors are presented for two types of muscle recruitment criteria.To sum up, there are still much to do regarding both the theoretical aspects as well as the practical implementations before predictions on one individual skier can be made with any certainty. But hopefully, this disseration somewhat furthers the fundamental mechanistic understanding of cross-country skiing, and shows that musculoskeletal biomechanics will be a useful complement to existing experimental methods in sports biomechanics.
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| 2. |
- Andersson, Håkan, 1970-
(författare)
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A Co-Simulation Tool Applied to Hydraulic Percussion Units
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this dissertation, a co-simulation tool is presented that is meant to comprise a more comprehensive environment for modelling and simulation of hydraulic percussion units, which are used in hydraulic hammers and rock drills. These units generates the large impact forces, which are needed to demolish concrete structures in the construction industry or to fragment rock when drilling blast holes in mine drifting. This type of machinery is driven by fluid power and is by that dependent of coupled fluid-structure mechanisms for their operation. This tool consists of a 1D fluid system model, a 3D structural mechanic model and an interface to establish the fluid-structure couplings, which has in this work been applied to a hydraulic hammer. This approach will enable virtual prototyping during product development with an ambition to reduce the need for testing of physical prototypes, but also to facilitate more detailed studies of internal mechanisms. The tool has been implemented for two well-known simulation tools, and a co-simulation interface to enable communication between them has been devel-oped. The fluid system is simulated using the Hopsan simulation tool and the structural parts are simulated using the FE-simulation software LS-DYNA. The implementation of the co-simulation interface is based on the Functional Mock-up Interface standard in Hopsan and on the User Defined Feature module in LS-DYNA. The basic functions of the tool were first verified for a simple but relevant model comprising co-simulation of one component, and secondly co-simulation of two components were verified. These models were based on rigid body and linear elastic representation of the structural components. Further, it was experimentally validated using an existing hydraulic hammer product, where the responses from the experiments were compared to the corresponding simulated responses. To investigate the effects from a parameter change, the hammer was operated and simulated at four different running conditions. Dynamic simulation of the sealing gap, which is a fundamental mechanism used for controlling the percussive motion, was implemented to further enhance the simulated responses of the percussion unit. This implementation is based on a parametrisation of the deformed FE-model, where the gap height and the eccentric position are estimated from the deformed geometry in the sealing gap region, and then the parameters are sent to the fluid simulation for a more accurate calculation of the leakage flow. Wear in percussion units is an undesirable type of damage, which may cause significant reduction in performance or complete break-down, and today there are no methodology available to evaluate such damages on virtual prototypes. A method to study wear was developed using the co-simulation tool to simulate the fundamental behaviour of the percussion unit, and the wear routines in LS-DYNA were utilised for the calculation of wear.
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| 3. |
- Andersson, Håkan, 1970-, et al.
(författare)
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Simulation of wear in hydraulic percussion units using a co-simulation approach
- 2023
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Ingår i: International Journal of Modelling and Simulation. - : Taylor & Francis. - 0228-6203 .- 1925-7082. ; 43:3, s. 265-281
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a developed co-simulation method, which couples 1D-fluid and 3D-structural models, has been utilised to simulate wear in a hydraulic percussion unit. The effect of wear is generally detrimental on performance and lifetime for such units, but can also cause catastrophic failure and breakdown, requiring a total overhaul and replacement of core components. One experiment of standard straight impact was performed to investigate the tolerance against seizure. The percussion unit was operated at successively increasing operating pressures, and the level of wear was registered at each step, until seizure occurred. The co-simulation model was used to replicate the running conditions from the experiment to simulate the structural response to be used as input for the wear routine to calculate the wear depth. The wear pattern from the simulations corresponds well to the wear pattern from the experiment. Further, the effect of a misaligned impact on wear development was also studied, as this is a loading situation that typically occurs for hydraulic percussion units. The study demonstrates that the simulation method used has a potential for simulating wear and predicting seizure in hydraulic percussion units.
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| 4. |
- Holmberg, Joakim, 1971-, et al.
(författare)
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Biomekaniska simuleringar adderar insikt om längdskidåkning
- 2010
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Ingår i: Svensk Idrottsforskning. - : Centrum för Idrottsforskning. - 1103-4629. ; 19:1, s. 38-40
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Varför ska man kopiera de som är bäst? När man väl lärt sig deras teknik så har de bästa kanske redan gått vidare och utvecklat ännu bättre tekniker? Med biomekaniska simuleringar adderas insikt så att man kan utveckla sin teknik och ligga i framkant, istället för i svallvågorna.
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| 5. |
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| 6. |
- Holmberg, Joakim L., 1971-
(författare)
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Computational Biomechanics in Cross-country Skiing
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traditionally, research on cross‐country skiing biomechanics is based mainly on experimental testing alone. Trying a different approach, this thesis explores the possibilities of using computational musculoskeletal biomechanics for cross‐country skiing. As far as the author knows, this has not been done before.Cross‐country skiing is both fast and powerful, and the whole body is used to generate movement. Consequently, the computational method used needs to be able to handle a full‐body model with lots of muscles. This thesis presents several simulation models created in the AnyBody Modeling System, which is based on inverse dynamics and static optimization. This method allows for measurementdriven full‐body models with hundreds of muscles and rigid body segments of all major body parts.A major result shown in the thesis is that with a good simulation model it is possible to predict muscle activation. Even though there is no claim of full validity of the simulation models, this result opens up a wide range of possibilities for computational musculoskeletal biomechanics in cross‐country skiing. Two example of new possibilities are shown in the thesis, finding antagonistic muscle pairs and muscle load distribution differences in different skiing styles. Being able to perform optimization studies and asking and answering “what if”‐questions really gives computational methods an edge compared to traditional testing.To conclude, a combination of computational and experimental methods seems to be the next logical step to increase the understanding of the biomechanics of crosscountry skiing.
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| 7. |
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| 8. |
- Holmberg, Joakim, 1971-
(författare)
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Simulera med mera
- 2008
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Ingår i: CAD & ritnytt. - Malmö : Skandinaviska CADmagasin. - 0282-5708. ; :4, s. 27-28
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Varför tillverkar man produkter utan att ta hänsyn till människan som ska använda dem? Är det inte konstigt att det nästan inte finns någon egenskap hos tekniska produkter som inte går att simulera, men ingen vet belastningen på din ryggrad när du sitter i din kontorsstol?
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| 9. |
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| 10. |
- Holmberg, L. Joakim, 1971-
(författare)
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A simulation study on the necessity of muscle contraction dynamics in cross-country skiing
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Competitive cross-country skiing is considered to be a fast and powerful dynamic movement. It is unknown what level of complexity that is needed in a musculoskeletal model of a skiing movement, e.g. double-poling. Therefore, a simulation study is carried out to explore the influence of muscle model choice. The theoretical framework of two types of muscle models and their respective implementations are given. These models are a Hill-type model with contraction dynamics and a constant force model, respectively. Results show that it is necessary to incorporate muscle contraction dynamics to estimate individual muscle behaviour in double-poling. Moreover, it may be bad practice to model different body parts with different muscle models; the musculoskeletal system is not a collection of discrete uncoupled body parts and kinetic effects will propagate through the system.
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| 11. |
- Holmberg, L. Joakim, 1971-
(författare)
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Biomekanisk simulering av längdskidåkning
- 2012
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Ingår i: Svensk idrottsmedicin. - Järna : Svensk Förening För Fysisk Aktivitet och Idrottmedicin. - 1103-7652. ; 31:3, s. 11-13
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 12. |
- Holmberg, L. Joakim, 1971-, et al.
(författare)
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Can Simulations Assist in Classification Development?
- 2013
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Ingår i: Equipment and Technology in Paralympic Sports. - : International Paralympic Committee.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There is a critical need for research that describes the extent to which impairments of varying type, severity and distribution impact performance in Paralympic sports. It is important with evidence-based judgment on how the impairments aect performance. In the following, we present a complementary evidence-based tool for classication.Let us start with an example. We recently presented a study (Holmberg et al., 2012)1 that utilized two full-body musculoskeletal simulation models of cross-country skiing (double-poling). The models were identical except that one carried no muscles in the right lower leg and foot; thus mimicking a lower leg prosthesis. It was hypothesized that a lower leg prosthesis would inuence muscular work throughout the whole body. Results showed that to generate the same motion and external work, an able-bodied skier only had to produce about 80% metabolic muscle work compared to a disabled skier (with a non-active right lower leg prosthesis).In reality there is always psychological factors present and it is probably not possible to nd two human beings (one fully functional and one impaired) with the same tness, size, strength and technique. Thus, it is hard to nd the unbiased eect of an impairment on performance in a speci c sport. The example above shows the strength of using simulations because a musculoskeletal model yields quantitative data on the unbiased eect of dierent functional impairments.In cross-country skiing, athletes with functional impairments are, in 'competition format' classification, assigned to dierent categories with weight factors. Athletes perform their race and the result list is presented as race time multiplied by weight factor. In the future, musculoskeletal simulations may assist in answering how a specic functional impairment aects performance and thereby improve the fairness in assigning weight factors for classication.
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| 13. |
- Holmberg, L. Joakim, 1971-, et al.
(författare)
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Muscle decomposition and recruitment criteria influence muscle force estimates
- 2012
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Ingår i: Multibody system dynamics. - : Springer. - 1384-5640 .- 1573-272X. ; 28:3, s. 283-289
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been pointed out that muscle decomposition influence muscle force estimates in musculoskeletal simulations. We show analytically and with numerical simulations that this influence depends on the recruitment criteria. Moreover, we also show that the proper choices of force normalization factors may overcome the issue. Such factors for the minmax and the polynomial criteria are presented.
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| 14. |
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| 15. |
- Lund Ohlsson, Marie, et al.
(författare)
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Evaulation of two sitting positions in Cross-Country Sit-Skiing
- 2016
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Ingår i: Abstract book of the 7th International Congress on Science and skiing. - 9783200048850
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- INTRODUCTION In cross-country sit-skiing (CCSS) athletes with reduced trunk control mainly sit with their knees higher than the hips (KH) to increase trunk stability. To improve the spine curvature by reducing kyphosis a new sitting position was created where the knees are lower than the hips by help of a forward trunk support (KL). The aim of this study was to evaluate the new KL position and compare it to KH in terms of physiological and biomechanical measurements as well as musculoskeletal simulations. METHODS Five abled-bodied female cross-country skiers (62.6±8.1kg, 1.67±0.05m) performed two sets of tests; one in each sitting position on a skiing ergometer (ThoraxTrainer A/S, Denmark). Each test comprised a 30s all-out test (AO), an incremental submaximal test (4 to 6 x 3 min, SUB1-SUB6) and a maximal time-trial test of 3 min (MAX). During SUB and MAX external power and kinematics were measured. Metabolic rates (MR) were calculated from oxygen consumption and lactate concentrations. The AnyBody Modelling system (AMS 6.0, Anybody Technology A/S, Denmark) were used to simulate full-body musculoskeletal models over 4 poling cycles of SUB2, SUB4 and MAX. From the simulations muscular metabolic rate (mMR) and musculo-skeletal efficiency (ME) were computed (Holmberg et al., 2013). RESULTS & DISCUSSION The performance (W/kg) was higher in KH (p < 0.01) in both AO (24%) and MAX (32%). KL had more flexed knee, more extended hip and less kyphosis in trunk, while KH had larger range of motion (ROM) in hip and larger flexion and ROM in spine at SUB4 and MAX. Gross efficiency (GE) was higher in KH than KL. The total MR and ratio of anaerobic MR to total MR were higher in KL at SUB3 and SUB4. Simulations showed that 4 subjects had higher ME in KH for both SUB4 and MAX, though no statistical significance were observed. mMR were higher for KL at SUB2 and SUB4 but it was higher for KH at MAX. The ratio of mMR in body parts to total mMR showed higher ratio for KL in arm-shoulders (6.7-9.1%) and higher ratio for KH in trunk (3.7-4.6%) and hip-legs (3.0-4.6%). CONCLUSION The physiological results were comparable to others (Lajunen, 2014 & Verellen et al, 2012) and the simulation results were novel by showing how the motion of the trunk contributes to the total metabolic rate. KH position showed higher performance and GE while the KL position indicated higher mMR for arm-shoulders, and had also higher anaerobic MR. Therefore the KH position is favorable for abled-bodied athletes because KL limits trunk motion. REFERENCES Holmberg, L. J. et al. (2013). Comput Methods Biomech Biomed Engin, 16(9), 987-992. Lajunen, K. (2014). Effect of sitting posture on sit-skiing economy. Bachelor’s thesis, University of Jyväskylä.Verellen, J. et al. (2012). Eur J Appl Physiol, 112(3), 983-989.
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| 16. |
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| 17. |
- Rasmussen, John, et al.
(författare)
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Performance optimization by musculoskeletal simulation
- 2012
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Ingår i: Movement & Sport Sciences – Science & Motricité. - Les Ulis, France : EDP Sciences. - 2118-5735 .- 2118-5743. ; 75, s. 73-83
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Tidskriftsartikel (refereegranskat)abstract
- This paper uses two examples, from cross country skiing and badminton, to illustrate the idea of using musculoskeletal simulation as a tool to understand and ultimately optimize sports performance. The results show that the analysis provides insight into the performances that cannot be obtained by other means, and it is advocated that this insight ultimately can lead to better coaching. The importance of “know-why” over “know-how” is stressed, and it is hypothesized that this may enable athletes to learn difficult techniques faster.
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| 18. |
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| 19. |
- Rovan, Klemen, et al.
(författare)
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The steps needed to perform acceleration and turning at different approach speeds
- 2014
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Ingår i: Kinesiologia Slovenica. - : University of Ljubljana. - 1318-2269 .- 2232-4062. ; 20:1, s. 38-50
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Tidskriftsartikel (refereegranskat)abstract
- The aims of the study were to examine: how many and which steps are needed to initiate and complete accelerations and turnings at different angles at different approach speeds; and how an intended turning angle and approach speed influence the magnitude of the actual turning angle in each step. Eight soccer players participated in the study. They performed acceleration and turnings: 1) from a standstill; 2) while already jogging; and 3) while already running on an outdoor soccer field. The speeds and angles were calculated from the data obtained from the high-end Global Navigation Satellite System. The high correlation between the intended turning angle and actual turning angle indicated the major turning steps during a turn. The intended turning angle revealed a large effect on the magnitude of the turning angle during the side-step (r = 0.995, p < 0.01) and the following step (r = 0.950, p < 0.01) for acceleration and turning from a standstill, and during the first two steps following the side-step for starts made while already jogging (r= 0.919, p < 0.01; r = 0.952, p < 0.01) and running (r = 0.897, p < 0.01; r = 0.881, p < 0.01). Further, a major part of the turning began earlier at a lower approach speed, which allowed the turning to be more quickly completed. In conclusion, the effect of acceleration with turning on the turning angle could already be seen two steps before and up to two steps after the major turning steps during a turn.
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