Inter-joint coordination changes during and after muscle fatigue.

Area of Science:

• Biomechanics
• Motor Control
• Human Physiology

Background:

• Human movement involves organizing numerous degrees of freedom into coordinated patterns.
• Inter-joint coordination is crucial for efficient multi-joint movements.
• Data decomposition techniques like principal component analysis (PCA) can identify these coordination patterns.

Purpose of the Study:

• To investigate how muscle fatigue affects inter-joint coordination during arm movements.
• To analyze changes in the covariance structure of multi-joint movements under fatigue conditions.
• To determine if movement strategies shift during and after fatigue.

Main Methods:

• Sixteen healthy adults performed a continuous ratcheting task with their right arm.
• A shoulder fatigue protocol was applied intermittently.
• Joint angle data from the arm and trunk were collected before, during, and after fatigue.
• Principal component analysis (PCA) was used to analyze joint angle covariance.
• Cross-correlations assessed changes in principal component waveforms during fatigue.

Main Results:

• The variance explained by the first four principal components decreased significantly during fatigue (90.5% pre-test to 86.0% fatigue).
• This reduction in explained variance indicates a decrease in inter-joint coordination.
• Movement patterns and principal component waveforms suggested a shift towards a more rigid movement strategy during fatigue.

Conclusions:

• Muscle fatigue leads to a decrease in inter-joint coordination.
• Fatigue induces a more rigid movement strategy, likely to maintain task performance.
• This rigid strategy was not observed post-fatigue, suggesting adaptation and the adoption of new coordination patterns with novel kinematics.