Optimality versus variability: effect of fatigue in multi-finger redundant tasks

Area of Science:

• Biomechanics
• Motor Control
• Human Physiology

Background:

• Understanding multi-finger synergies is crucial for grasping tasks.
• Fatigue-induced changes in motor control are not fully understood.
• Investigating how the nervous system adapts finger coordination under fatigue is essential.

Purpose of the Study:

• To analyze changes in multi-finger synergies after index finger fatigue.
• To identify cost functions and quantify force co-variation before and during fatigue.
• To explore the role of agonist vs. antagonist muscle function in motor adaptation.

Main Methods:

• Used analytical inverse optimization (ANIO) to determine optimal solutions.
• Applied uncontrolled manifold (UCM) hypothesis to assess force variability.
• Induced fatigue via index finger maximal voluntary contraction.
• Utilized principal component (PC) analysis to analyze finger force patterns.

Main Results:

• Quadratic cost functions were estimated, with a small dihedral angle that increased with fatigue.
• Fatigue altered force cost functions, increasing index finger contribution and decreasing others.
• Co-variation indices changed with fatigue, depending on whether the finger acted as an agonist or antagonist.

Conclusions:

• Motor adaptation to fatigue involves changes in finger force synergies.
• Stabilizing performance during fatigue may depend on the fatigued finger's functional role.
• Findings suggest task-specific adaptations in motor control strategies post-fatigue.