Proximal and distal muscle fatigue differentially affect movement coordination

Area of Science:

• Biomechanics
• Human Movement Science
• Occupational Health

Background:

• Muscle fatigue is a known contributor to altered movement patterns.
• These kinematic changes can increase the risk of acute or overuse injuries.
• The specific effects of fatigue depend on the location of the fatigued muscles (proximal vs. distal).

Purpose of the Study:

• To investigate the differential effects of proximal (shoulder flexor) and distal (finger flexor) upper extremity muscle fatigue on repetitive movements.
• To compare kinematic changes and movement variability following distinct muscle fatigue protocols.

Main Methods:

• Fourteen subjects performed a repetitive ratcheting task.
• Fatigue was induced separately for proximal and distal upper extremity muscles.
• Kinematic data (trunk, shoulder, elbow, wrist) were collected and analyzed pre- and post-fatigue.

Main Results:

• Proximal fatigue led to increased trunk lean/velocity, reduced shoulder elevation, and increased elbow flexion.
• Distal fatigue resulted in minor trunk angle changes, increased tool velocity relative to hand, and earlier wrist extension.
• Movement variability increased at proximal joints after both fatigue types, but not at distal joints.

Conclusions:

• Proximal and distal muscle fatigue induce distinct kinematic adaptations in the upper extremity.
• Increased proximal joint variability may serve as a compensatory mechanism for fatigue.
• Understanding these differences can aid in assessing occupational task risks.