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- Domkin, Dmitry, et al.
(författare)
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Structure of joint variability in bimanual pointing tasks
- 2002
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Ingår i: Experimental Brain Research. - : Springer Science and Business Media LLC. - 0014-4819 .- 1432-1106. ; 143, s. 11-23
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the structure of motor variability during practicing a bimanual pointing task were investigated using the framework of the uncontrolled manifold (UCM) hypothesis. The subjects performed fast and accurate planar movements with both arms, one moving the pointer and the other moving the target. The UCM hypothesis predicts that joint kinematic variability will be structured to selectively stabilize important task variables. This prediction was tested with respect to selective stabilization of the trajectory of the endpoint of each arm (unimanual control hypotheses) and with respect to selective stabilization of the timecourse of the vectorial distance between the target and the pointer tip (bimanual control hypothesis). Components of joint position variance not affecting and affecting a mean value of a selected variable were computed at each 10% of normalized movement time. The ratio of these two components ( R(V)) served as a quantitative index of selective stabilization. Both unimanual control hypotheses and the bimanual control hypothesis were supported both prior to and after practice. However, the R(V) values for the bimanual control hypothesis were significantly higher than for either of the unimanual control hypothesis, suggesting that the bimanual synergy was not simply a simultaneous execution of two unimanual synergies. After practice, an improvement in both movement speed and accuracy was accompanied by counterintuitive changes in the structure of kinematic variability. Components of joint position variance affecting and not affecting a mean value of a selected variable decreased, but there was a significantly larger drop in the latter when applied on each of the three selected task variables corresponding to the three control hypotheses. We conclude that the UCM hypothesis allows quantitative assessment of the degree of stabilization of selected performance variables and provides information on changes in the structure of a multijoint synergy that may not be reflected in its overall performance.
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| 2. |
- Nakata, Minori, et al.
(författare)
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Evaluation of workload in ambulance personnel - A preliminary study
- 2002
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Ingår i: Humans in a Complex Environment. - 9173734438
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Konferensbidrag (refereegranskat)abstract
- Musculotendinous tenderness was evaluated in ambulance personnel, and their working load was studied by means of biomechanical analysis of the standard loading and unloading the `stretcher+patient' in and from the vehicle. Swedish and Japanese subjects were tested. The medical examination demonstrated increased tenderness of selected muscles active in work related movement tasks, as well as in spinous processes in both populations. However, a number ofparticular tests suggested higher Ievel of tenderness in the Swedish, as compared with the Japanese personnel. Biomechanical analysis of working tasks demonstrated similar forces, but higher LS-SI, hip and shoulder torques acting in Swedish personnel. This difference appears to be caused by the differences in stretcher construction. Specifically, the Swedish stretcher requires separate lifting of each stretcher side starting from a squat body position, while the Japanese system requires only pushing the stretcher in and pulling it out from the vehicle. We conclude that differences in working technique imposed by available working equipment could contribute to the observed differences in muscle tenderness especially around the shoulders between the two tested populations. However, further studies are needed to elaborate working load and muscle activity while performing standard tasks of ambulance personnel, as well as to explore other possible causes of increased musculotendinous tenderness. Keywords: Ambulance, Muculoskeletal disorders, Muscle tenderness, Spinous process, Biomechanical analyses
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