Interjoint coordination in lower limbs during different movements in humans.

Area of Science:

• Biomechanics and Motor Control
• Neuroscience
• Human Movement Analysis

Background:

• The nervous system exhibits redundancy, enabling flexible control of multiple degrees of freedom (DF) through task-specific synergies.
• Understanding how the nervous system coordinates interjoint movements is crucial for deciphering motor control strategies.

Purpose of the Study:

• To investigate interjoint coordination during various motor tasks using principal component (PC) analysis.
• To determine the number and nature of synergies underlying different human movements.

Main Methods:

• Principal component (PC) analysis was applied to angular changes in four DF (thigh flexion-extension, knee flexion-extension, ankle flexion-extension, thigh abduction-adduction) during eight distinct movements in healthy male subjects.
• Analysis focused on quantifying the contribution of synergies to overall joint angular excursions.

Main Results:

• Two synergies were sufficient to explain over 95% of DF angular excursions for most movements.
• Squatting on one leg was explained by a single synergy (99%).
• Inter-leg coordination showed some differences, and a common, adjustable basic synergy was identified across different movements, with additional synergies facilitating transitions.

Conclusions:

• The nervous system employs a limited number of synergies to control complex movements, demonstrating efficient coordination of multiple degrees of freedom.
• A core, adaptable synergy likely underlies various movements, supplemented by task-specific synergies for nuanced control and transitions.