| 1. |
- Arborelius, U P, et al.
(author)
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The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising
- 1992
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In: Ergonomics. - : Taylor & Francis. - 0014-0139 .- 1366-5847. ; 35:11, s. 1377-1391
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Journal article (peer-reviewed)abstract
- The loading moment of force on the hip, knee, and ankle joints of nine healthy men rising from four different types of stools were compared, together with the levels of myoelectrical activity (EMG) in four leg muscles. Two types of stool (stand stools) had higher seats than a normal chair. The other two were of ordinary seat height, but one also had armrests. The bodyweight carried by the different stools when sitting was also measured, and the subject estimated the effort required for each trial. The mean maximum knee moment was over 60% lower when rising from the high stool than from 'ordinary' seat height. The difference between the high and low stand stool was also significant (p less than 0.001). Using the high stool or help of the arms reduced the mean maximum hip moment by about 50%. The mean maximum ankle moment was only marginally influenced by the different stools. Knee moment was influenced more by seat height than was hip moment. Vastus lateralis activity was significantly higher when subjects rose from 'ordinary' height than when rising from either stand stool (p less than 0.001). The rectus femoris muscle was little activated and the semitendinosus muscle was activated earlier when rising from higher seat heights. All subjects estimated the effort of rising from the higher stand stool to be lower than from the lower stand stool or from 'ordinary' height without arm rests. It was concluded that stand stools are good alternatives for workers who change frequently between sitting and standing work.
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| 2. |
- Wretenberg, Per, 1963-, et al.
(author)
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Effect of armrests and different ways of using them on hip and knee load during rising
- 1993
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In: Clinical Biomechanics. - Oxon, United Kingdom : Butterworth-Heinemann. - 0268-0033 .- 1879-1271. ; 8:2, s. 95-101
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Journal article (peer-reviewed)abstract
- The loading moments of force about the hip and knee joints of ten healthy male subjects were calculated using recorded forces from a force plate and static contribution from body segments. The subjects rose from a chair while using armrests in ten different ways, and, as a reference, without arm aid. The influence of different armrest heights, hand placements and arm forces was studied. Horizontal and vertical forces on the armrests were measured. Irrespective of armrest height and hand placement, the use of armrests significantly reduced the hip and knee moments compared to rising without arm aid (P < 0.001). However, there were no statistically significant differences between different armrest heights or hand placements. High arm force reduced both hip and knee moments. The greatest reduction occurred for high armrests and high arm force, which reduced the mean peak hip moment from 39 to 17 N m and the knee moment from 83 to 28 N m. Calculation of patellofemoral compressive force and the force on the femoral head due to extensor muscle activity demonstrated that local hip and knee forces were reduced when armrests were used. Horizontal forces applied to the armrests were small. Subjectively 'doubled' arm force resulted in nearly double force on the armrests.
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| 3. |
- Wretenberg, Per, 1963-, et al.
(author)
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Power and work produced in different leg muscle groups when rising from a chair
- 1994
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In: European Journal of Applied Physiology and Occupational Physiology. - New York, USA : Springer. - 0301-5548 .- 1432-1025. ; 68:5, s. 413-417
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Journal article (peer-reviewed)abstract
- The aim of this study was to determine the power output and work done by different muscle groups at the hip and knee joints during a rising movement, to be able to tell the degree of activation of the muscle groups and the relationship between concentric and eccentric work. Nine healthy male subjects rose from a chair with the seat at knee level. The moments of force about the hip and knee joints were calculated semidynamically. The power output (P) and work in the different muscle groups surrounding the joints was calculated as moment of force times joint angular velocity. Work was calculated as: work = integral of P dt. The mean peak concentric power output was for the hip extensors 49.9 W, hip flexors 7.9 W and knee extensor 89.5 W. This power output corresponded to a net concentric work of 20.7 J, 1.0 J and 55.6 J, respectively. There was no concentric power output from the knee flexor muscles. Energy absorption through eccentric muscle action was produced by the hip extensors and hip flexors with a mean peak power output of 4.8 W and 7.4 W, respectively. It was concluded that during rising, the hip and knee muscles mainly worked concentrically and that the greatest power output and work were produced during concentric contraction of the knee and hip extensor muscles. There was however also a demand for eccentric work by the hip extensors as well as both concentric and eccentric work by the hip flexors. The knee flexor muscles were unloaded.
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| 4. |
- Wretenberg, Per, 1963-, et al.
(author)
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Rising from a chair by a spring-loaded flap seat : a biomechanical analysis
- 1993
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In: Scandinavian Journal of Rehabilitation Medicine. - Oslo, Norway : Scandinavian University Press. - 0036-5505 .- 1940-2228. ; 25:4, s. 153-159
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Journal article (peer-reviewed)abstract
- Nine healthy male subjects and 8 patients with unilateral knee osteoarthrosis were studied while rising from a chair with and without the aid of a spring-loaded flap seat. The seat force started at 216 N and decreased with increasing seat angle. Ground reaction forces and motion were recorded using a force plate and video. EMG of the left vastus lateralis muscle was recorded. The effort when rising was estimated by the Borg scale. The use of the flap seat reduced the mean peak knee moment for the healthy subjects from 73 to 41 Nm and for the patients from 55 to 33 Nm. The decreases were significant at a p < 0.001 level. The patients also reduced their hip moment significantly from 50 to 35 Nm (p < 0.005). The muscle activity in the vastus lateralis was also significantly lower when the flap seat was used (p < 0.005). When the theoretically maximal friction force between seat and subject was added, the effective seat force decreased more slowly, and the relation between its horizontal and vertical force components was more advantageous. The patients estimated greater effort reduction than the healthy subjects comparing the ordinary chair and the flap seat.Conclusion: a spring-loaded flap seat can reduce knee and hip load and can thus be useful for people with knee osteoarthrosis.
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| 5. |
- Wretenberg, Per, 1963-, et al.
(author)
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The effects of a pneumatic stool and a one-legged stool on lower limb joint load and muscular activity during sitting and rising
- 1993
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In: Ergonomics. - London, United Kingdom : Taylor & Francis. - 0014-0139 .- 1366-5847. ; 36:5, s. 519-535
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Journal article (peer-reviewed)abstract
- Nine healthy male subjects rose from four different stools. The 'ordinary' stool (K) was set at normal chair height, approximately 50 cm, and the 'low ordinary' stool (O), the one-legged stool (T), and the pneumatically-sprung stool (S) were all approximately 32 cm high. The moments of force in the hip, knee, and ankle joints were calculated with a semidynamic technique using a Kistler force plate and video. EMG in four leg muscles was recorded. The part of bodyweight carried by the different stools when the subjects were sitting was measured, and the subjects estimated the effort of rising, using the Borg scale. The low ordinary stool gave higher knee and hip moments than the ordinary stool. Use of the pneumatic stool reduced the knee and hip moments to a level comparable with that of the ordinary stool. The reduction in moment compared with the one-legged stool (T) and the low ordinary stool (O) was significant, both in the knee (p < 0.005) and the hip (p < 0.001). Rising from the three low stools gave no significant differences in mean maximum muscle activity in any of the muscles investigated. The subjects estimated that the pneumatic stool and the ordinary stool were the easiest to rise from. The part of bodyweight carried by the ordinary stool and the low ordinary stool, both around 80% when sitting, was significantly higher than for the two other stools (p < 0.005). It was concluded that a pneumatic stool can be a useful device to workers who work in low positions and rise frequently.
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