Characterization of age-related modifications of upper limb motor control strategies in a new dynamic environment
In the past two decades, many research groups have shown that when velocity dependent force field is applied to arm motion, subjects learn to compensate for the external perturbation and return a linear path. Thus, adaptation to a novel condition consists of creating an Internal Model of the new environment which is included in the normal unperturbed motor commands to achieve good performances.
The efficiency of this motor control mechanism can be compromised by the presence of a pathological disorders or by muscular-skeletal modifications such as the ones connected to natural aging process. In this respect, the present study aimed at identifying the age-related modifications in upper limb motor control strategies during adaptation and de-adaptation processes.
Methods: Eight young and eight elderly healthy subjects, were included in the experiment. Subjects were instructed to perform pointing movements in the horizontal plane both in a null field and in a velocity dependent force field .
The evolution of smoothness and hand path parameters were evaluated as coordination characteristics of human movements. Furthermore, the ability of modulating the interactive torque have been used as a paradigm to explain the observed discoordinated patterns during the adaptation process.
Results: The evolution of the kinematics characteristics during the experiment highlight important behavioural differences between the two groups during the adaptation and de-adaptation processes.
Young subjects improvement of movements smoothness was in accordance with the expected learning trend related to the consolidation of the internal model both in the adaptation and in de-adaptation phases. Elders did not show a coherent learning process and needed a more prolonged training to achieve the same performances of young subjects.
The kinetic analysis pointed out the presence of different strategies for the compensation of the external perturbation, which in the case of older people required the involvement of the shoulder and results in a different modulation of joints torque components during the evolution of the experiments.
Conclusions: The results obtained with the present study seemed to confirm what has been claimed in past works about the presence of different mechanisms influencing motor adaptation related both to kinematic and dynamic recovery. The strategy adopted by young subjects attempted to first minimize hand path errors during adaptation and de-adaptation phases, but provided evidence for a secondary process that is consistent with the optimization of the effort.
Elderly subjects instead, seemed to shift the importance of the two processes involved in the control loop slowing the mechanism optimizing kinematic performance and enabling more the dynamic adaptation mechanism.
Author: Benedetta Cesqui, Giovanna Macri, Paolo Dario and Silvestro Micera
Credits/Source: Journal of NeuroEngineering and Rehabilitation 2008, 5:31
Published on: 2008-11-19
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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