Muscular synergism--II. A minimum-fatigue criterion for load sharing between synergistic muscles

Area of Science:

• Biomechanics
• Human Physiology
• Muscle Physiology

Background:

• Understanding muscle load sharing is crucial for analyzing movement and preventing injury.
• Existing models do not fully capture the complex interplay of factors influencing muscle force allocation.
• Minimizing muscular fatigue is a key physiological objective during sustained activity.

Purpose of the Study:

• To develop a novel physiological criterion for predicting muscular load sharing.
• To establish a framework for minimizing muscular fatigue during contractions.
• To investigate the relationship between muscle properties and force distribution.

Main Methods:

• Formulated an optimization problem based on maximizing muscular endurance time.
• Employed a linearly constrained, non-linear MINIMAX optimization approach.
• Predicted muscle force allocation based on muscle maximum force and fiber type composition.

Main Results:

• Predicted synergistic muscle action, where multiple muscles cooperate.
• Demonstrated non-linear increases in muscle force with external load.
• Showed preferential force allocation to larger muscles and fatigue-resistant (slow-twitch) fibers.
• Found that load sharing is independent of muscle moment arm, though absolute forces are dependent.

Conclusions:

• The developed criterion provides a new physiological basis for understanding muscle force distribution.
• The model accurately predicts synergistic muscle action and preferential recruitment of fatigue-resistant fibers.
• Predictions align with experimental data for cat hindlimb muscles during locomotion, validating the criterion.