MUSCLE FORCE AS AFFECTED BY FATIGUE - MATHEMATICAL-MODEL AND EXPERIMENTAL-VERIFICATION

The effects of muscle fatigue have been included in a comprehensive mu scle 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 consider ed in the model derivation. Fiber force is modified using indices of f atigue which were derived based on the data from experimental work con ducted by others. In this paper, derivations of the indices for each o f the fiber types are presented. An elbow extension study was performe d to validate the modeled fatigue relationship for maximal effort acti vities. Triceps brachii forces generated during both isometric and dyn amic fatigue tests were determined using both the muscle model and a d irect approach based on rigid-body dynamics. The forces obtained from the two approaches were not significantly different for times either l ess than 50 s for the isometric tests, or greater than 40 s for the dy namic tests. Results from the statistical comparison indicate the util ity of the modeling approach presented.