Adaptive increase in force variance during fatigue in tasks with low redundancy

Area of Science:

• Neuroscience
• Motor Control
• Biomechanics

Background:

• Fatigue is a common challenge affecting motor performance.
• The central nervous system (CNS) may employ adaptive strategies to counteract fatigue.
• Understanding neural adaptations to fatigue is crucial for rehabilitation and performance enhancement.

Purpose of the Study:

• To test the hypothesis that finger fatigue induces adaptive neural strategies.
• To investigate if increased force variability in one finger and co-variation in others maintain total force stability.
• To examine these adaptations in systems with varying degrees of redundancy.

Main Methods:

• Subjects performed isometric rhythmic force production tasks with one (index finger) or two fingers (index and middle).
• A fatiguing exercise targeted the index finger before and after the tasks.
• Force variability and co-variation of finger commands were quantified using finger modes under stable and unstable conditions.

Main Results:

• Fatigue significantly increased force variance in the single-finger task and less so in the two-finger task.
• A larger increase in the force-unaffecting variance component and a smaller increase in the force-affecting component were observed.
• An index of force-stabilizing synergy increased, indicating enhanced stability despite fatigue.

Conclusions:

• Marginal redundancy is sufficient for the CNS to adapt to fatigue by increasing variability.
• The CNS can shield important variables from fatigue effects through adaptive neural strategies.
• Results support the referent configuration hypothesis, a development of the equilibrium-point hypothesis.