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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.


Related in: MedlinePlus

Catch trial trajectories of individual subjects.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block), grey lines show the mean COM trajectories during induced perturbation (P block), and the green lines show the mean COM trajectories during the catch trails (C blocks). The catch trial trajectories of all subjects are curved in the opposite direction to the perturbed trajectories. Besides, the catch trial trajectories lie well beyond the unperturbed trajectories. This suggests that all subjects actively compensated the perturbations and not merely moved as when they were moving on the still platform. The shades represent the 95% confidence interval.
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f5: Catch trial trajectories of individual subjects.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block), grey lines show the mean COM trajectories during induced perturbation (P block), and the green lines show the mean COM trajectories during the catch trails (C blocks). The catch trial trajectories of all subjects are curved in the opposite direction to the perturbed trajectories. Besides, the catch trial trajectories lie well beyond the unperturbed trajectories. This suggests that all subjects actively compensated the perturbations and not merely moved as when they were moving on the still platform. The shades represent the 95% confidence interval.

Mentions: We used catch trials in C blocks to check the deviation of the COM trajectory (aftereffect) when the perturbation was unexpectedly turned off. The catch trials were introduced after the adaptation stabilized to uncover the adaptation mechanism adopted by the subjects. The C blocks trials had COM trajectories that were curved in the opposite direction to those of the P block (Fig. 5). Furthermore, the C blocks COM trajectories lie well beyond the U block COM trajectories. Their average duration was 1.06 ± 0.106(SD) s which is not significantly different from the duration of neither unperturbed nor perturbed trials. Statistical analysis confirmed that these trajectories are significantly different from the U block trajectories, t(7) = 6.50, p < .000 (Supplementary Fig. S2). This rules out a naive explanation that during the catch trials subjects simply moved as when they were moving on the still platform (U block) and suggests that the subjects actively compensated the perturbation.


Human motor adaptation in whole body motion
Catch trial trajectories of individual subjects.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block), grey lines show the mean COM trajectories during induced perturbation (P block), and the green lines show the mean COM trajectories during the catch trails (C blocks). The catch trial trajectories of all subjects are curved in the opposite direction to the perturbed trajectories. Besides, the catch trial trajectories lie well beyond the unperturbed trajectories. This suggests that all subjects actively compensated the perturbations and not merely moved as when they were moving on the still platform. 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

f5: Catch trial trajectories of individual subjects.Pink lines show the mean center-of-mass (COM) trajectories of the squat-to-stand motions without perturbation (U block), grey lines show the mean COM trajectories during induced perturbation (P block), and the green lines show the mean COM trajectories during the catch trails (C blocks). The catch trial trajectories of all subjects are curved in the opposite direction to the perturbed trajectories. Besides, the catch trial trajectories lie well beyond the unperturbed trajectories. This suggests that all subjects actively compensated the perturbations and not merely moved as when they were moving on the still platform. The shades represent the 95% confidence interval.
Mentions: We used catch trials in C blocks to check the deviation of the COM trajectory (aftereffect) when the perturbation was unexpectedly turned off. The catch trials were introduced after the adaptation stabilized to uncover the adaptation mechanism adopted by the subjects. The C blocks trials had COM trajectories that were curved in the opposite direction to those of the P block (Fig. 5). Furthermore, the C blocks COM trajectories lie well beyond the U block COM trajectories. Their average duration was 1.06 ± 0.106(SD) s which is not significantly different from the duration of neither unperturbed nor perturbed trials. Statistical analysis confirmed that these trajectories are significantly different from the U block trajectories, t(7) = 6.50, p < .000 (Supplementary Fig. S2). This rules out a naive explanation that during the catch trials subjects simply moved as when they were moving on the still platform (U block) and suggests that the subjects actively compensated the perturbation.

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.


Related in: MedlinePlus