Muscle force as affected by fatigue: mathematical model and experimental verification.

Abstract

The effects of muscle fatigue have been included in a comprehensive muscle model derivation. The fiber-based muscle model calculates muscle force as the sum of individual fiber forces, determined based on fiber kinematics and activation information. Three fiber types are considered in the model derivation. Fiber force is modified using indices of fatigue which were derived based on the data from experimental work conducted by others. In this paper, derivations of the indices for each of the fiber types are presented. An elbow extension study was performed to validate the modeled fatigue relationship for maximal effort activities. Triceps brachii forces generated during both isometric and dynamic fatigue tests were determined using both the muscle model and a direct approach based on rigid-body dynamics. The forces obtained from the two approaches were not significantly different for times either less than 50 s for the isometric tests, or greater than 40 s for the dynamic tests. Results from the statistical comparison indicate the utility of the modeling approach presented.