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Human motor adaptation in whole body motion

View Article: PubMed Central - PubMed

ABSTRACT

The main role of the sensorimotor system of an organism is to increase the survival of the species. Therefore, to understand the adaptation and optimality mechanisms of motor control, it is necessary to study the sensorimotor system in terms of ecological fitness. We designed an experimental paradigm that exposed sensorimotor system to risk of injury. We studied human subjects performing uncon- strained squat-to-stand movements that were systematically subjected to non-trivial perturbation. We found that subjects adapted by actively compensating the perturbations, converging to movements that were different from their normal unperturbed squat-to-stand movements. Furthermore, the adapted movements had clear intrinsic inter-subject differences which could be explained by different adapta- tion strategies employed by the subjects. These results suggest that classical optimality measures of physical energy and task satisfaction should be seen as part of a hierarchical organization of optimality with safety being at the highest level. Therefore, in addition to physical energy and task fulfillment, the risk of injury and other possible costs such as neural computational overhead have to be considered when analyzing human movement.

No MeSH data available.


Adaptations to perturbation for each individual subject.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block) while the grey-shaded lines show the COM trajectories during induced perturbation (P blocks). The lightest grey lines show the mean COM trajectories of the first perturbed block, the darkest grey lines show the mean COM trajectories of the third perturbed block when the subjects already adapted to the perturbation, and the medium grey line represent the block in-between. The shades represent the 95% confidence interval.
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f2: Adaptations to perturbation for each individual subject.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block) while the grey-shaded lines show the COM trajectories during induced perturbation (P blocks). The lightest grey lines show the mean COM trajectories of the first perturbed block, the darkest grey lines show the mean COM trajectories of the third perturbed block when the subjects already adapted to the perturbation, and the medium grey line represent the block in-between. The shades represent the 95% confidence interval.

Mentions: The squat-to-stand trials without perturbation (U block) showed a near-straight COM trajectories across all subjects. These trials were quite consistent, and had a slight curvature in the posterior direction (leftwards in the trajectory figures and downwards in the statistical figure). Their average duration was 0.90 ± 0.078(SD) s. The first perturbed block (P block) for each subject reflected the expected COM trajectory perturbation: the trajectories became curved towards the anterior direction (rightwards in the trajectory figures and upwards in the statistical figure). This was expected as the perturbation towards the posterior direction caused the feet to be carried posteriorly with respect to the subject’s COM (assuming no foot slip), hence the subject’s COM moved in the anterior direction with regard to the feet and the platform. A typical displacement of the platform in the posterior direction was approximately 8 cm and was always much larger than the maximal COM displacement in the anterior direction. Thus, the COM motion was not a physically trivial counteraction to the platform motion. In the following P blocks the deviation from the unperturbed trajectories visibly reduced (Fig. 2). The average duration of perturbation trials was 0.96 ± 0.059(SD) s which is not significantly different from the duration of unperturbed trials.


Human motor adaptation in whole body motion
Adaptations to perturbation for each individual subject.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block) while the grey-shaded lines show the COM trajectories during induced perturbation (P blocks). The lightest grey lines show the mean COM trajectories of the first perturbed block, the darkest grey lines show the mean COM trajectories of the third perturbed block when the subjects already adapted to the perturbation, and the medium grey line represent the block in-between. The shades represent the 95% confidence interval.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016968&req=5

f2: Adaptations to perturbation for each individual subject.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block) while the grey-shaded lines show the COM trajectories during induced perturbation (P blocks). The lightest grey lines show the mean COM trajectories of the first perturbed block, the darkest grey lines show the mean COM trajectories of the third perturbed block when the subjects already adapted to the perturbation, and the medium grey line represent the block in-between. The shades represent the 95% confidence interval.
Mentions: The squat-to-stand trials without perturbation (U block) showed a near-straight COM trajectories across all subjects. These trials were quite consistent, and had a slight curvature in the posterior direction (leftwards in the trajectory figures and downwards in the statistical figure). Their average duration was 0.90 ± 0.078(SD) s. The first perturbed block (P block) for each subject reflected the expected COM trajectory perturbation: the trajectories became curved towards the anterior direction (rightwards in the trajectory figures and upwards in the statistical figure). This was expected as the perturbation towards the posterior direction caused the feet to be carried posteriorly with respect to the subject’s COM (assuming no foot slip), hence the subject’s COM moved in the anterior direction with regard to the feet and the platform. A typical displacement of the platform in the posterior direction was approximately 8 cm and was always much larger than the maximal COM displacement in the anterior direction. Thus, the COM motion was not a physically trivial counteraction to the platform motion. In the following P blocks the deviation from the unperturbed trajectories visibly reduced (Fig. 2). The average duration of perturbation trials was 0.96 ± 0.059(SD) s which is not significantly different from the duration of unperturbed trials.

View Article: PubMed Central - PubMed

ABSTRACT

The main role of the sensorimotor system of an organism is to increase the survival of the species. Therefore, to understand the adaptation and optimality mechanisms of motor control, it is necessary to study the sensorimotor system in terms of ecological fitness. We designed an experimental paradigm that exposed sensorimotor system to risk of injury. We studied human subjects performing uncon- strained squat-to-stand movements that were systematically subjected to non-trivial perturbation. We found that subjects adapted by actively compensating the perturbations, converging to movements that were different from their normal unperturbed squat-to-stand movements. Furthermore, the adapted movements had clear intrinsic inter-subject differences which could be explained by different adapta- tion strategies employed by the subjects. These results suggest that classical optimality measures of physical energy and task satisfaction should be seen as part of a hierarchical organization of optimality with safety being at the highest level. Therefore, in addition to physical energy and task fulfillment, the risk of injury and other possible costs such as neural computational overhead have to be considered when analyzing human movement.

No MeSH data available.