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- Aasa, Ulrika, et al.
(författare)
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Normalisation of muscle strength for body size : The role of the function assessed
- 2004
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Ingår i: Journal of Human Movement Studies. - 0306-7297. ; 46:2, s. 105-116
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Tidskriftsartikel (refereegranskat)abstract
- The role of body size has often been neglected in routine tests of muscle strength and movement performance. The aim of the present study was to test the hypothesis that different types of functional movement performance require different normalisations in order to assess muscle strength. Twenty-one right-handed male university students were tested on the following functional movement tasks: vertical jump, standing soccer ball kick, seated medicine ball throw and standing maximal isometric lift. Isokinetic strength of active muscle \, groups was also recorded. The performance of the vertical jump and standing s9ccer ball kick demonstrated stronger relationship with the strength of active muscles normalised for body size, while the performance of the s~ated medicine ball throw and standing maximal Iisometric lift demonstrated stronger relationship with the non- normalised strength. It was concluded that the ability of performing functional movements based on overcoming gravitational and/or inertial resistance of subject's own body (such as keeping certain body postures, or various body movements) should be assessed by the tested muscle strength normalised for body size, while the functional performance based on muscle action performed against external objects (e.g. manual material handling, or lifting heavy objects) should be assessed by the non-normalised muscle strength. The obtained f"mdings proved to be in line with our recently proposed classification of muscle strength and functional movement tests based on the role of body size in the re~orded performance.
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| 2. |
- Domkin, Dmitry, et al.
(författare)
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Joint angle variability in 3D bimanual pointing : uncontrolled manifold analysis.
- 2005
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Ingår i: Experimental Brain Research. - : Springer Science and Business Media LLC. - 0014-4819 .- 1432-1106. ; 163:1, s. 44-57
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Tidskriftsartikel (refereegranskat)abstract
- The structure of joint angle variability and its changes with practice were investigated using the uncontrolled manifold (UCM) computational approach. Subjects performed fast and accurate bimanual pointing movements in 3D space, trying to match the tip of a pointer, held in the right hand, with the tip of one of three different targets, held in the left hand during a pre-test, several practice sessions and a post-test. The prediction of the UCM approach about the structuring of joint angle variance for selective stabilization of important task variables was tested with respect to selective stabilization of time series of the vectorial distance between the pointer and aimed target tips (bimanual control hypothesis) and with respect to selective stabilization of the endpoint trajectory of each arm (unimanual control hypothesis). The components of the total joint angle variance not affecting (V(COMP)) and affecting (V(UN)) the value of a selected task variable were computed for each 10% of the normalized movement time. The ratio of these two components R(V)=V(COMP)/V(UN) served as a quantitative index of selective stabilization. Both the bimanual and unimanual control hypotheses were supported, however the R(V) values for the bimanual hypothesis were significantly higher than those for the unimanual hypothesis applied to the left and right arm both prior to and after practice. This suggests that the CNS stabilizes the relative trajectory of one endpoint with respect to the other more than it stabilizes the trajectories of each of the endpoints in the external space. Practice-associated improvement in both movement speed and accuracy was accompanied by counter-intuitive lack of changes in R(V). Both V(COMP) and V(UN) variance components decreased such that their ratio remained constant prior to and after practice. We conclude that the UCM approach offers a unique and under-explored opportunity to track changes in the organization of multi-effector systems with practice and allows quantitative assessment of the degree of stabilization of selected performance variables.
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| 3. |
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| 4. |
- 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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| 5. |
- Laczko, Jozsef, et al.
(författare)
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Stabilization of kinematic variables in the control of bimanual pointing movements
- 2001
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Ingår i: Proceedings of the International joint conference on neural networks. ; , s. 1256-1260
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Konferensbidrag (refereegranskat)abstract
- Human voluntary movements face a problem of kinematic redundancy: The number of degrees of freedom for the peripheral mechanical apparatus (e.g., a Iimb) is higher than the number of variables necessary to describe movement execution. Thus, there is an infinity of different ways to execute a given motor task. The recently developed Uncontrolled Manifold (UCM) hypothesis suggests that the central nervous system (CNS) generates solutions such that important task related variables are selectively stabilized. Each motor task is associated with stabilizing a .time series of a task variable. At each instant, the CNS selects, in the state space af elements participating in the task, a manifold (UCM) corresponding to a fixed value of the selected task variable. We study a planar bìmanual task, when one hand moves a target and the other hand moves a pointer that must reach the target. We hypothesized that the stabilized task variable was the vectorial difference of the pointertip and the target. The 6 dimensional state space was defined bys 'joint configuration vectors" whose elements were intersegmental joint angles (shoulder, elbow and wrisst in both arms). The subjects repeated the movements IS times, and the movements were recorded by a movement analysis system. Then, the subjects practiced the movements (300 trials). After practice IS trials were recorded again. We computed the variance of the joint configurations before and after practice. Six joint rotations affected the 2 dimensional task variable. The UCM corresponding to this variable is 4- dimensional, while the subspace of the state space that is orthogonal (ORT) to the UCM is 2-dimensional. The variance within the UCM was larger than in the ORT conforming to the UCM hyphothesis. After practice the joint variance decreased and the drop in the component of variance that did not affect the task vaeriable was larger thnn the drop 'of the other component. Thus, practice lead to more stable time courses of the task variable and of the corresponding joint configuration.
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| 8. |
- 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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