A predictive model of fatigue in human skeletal muscles

Fatigue is a major limitation to the clinical application of functional ele ctrical stimulation. The activation pattern used during electrical stimulat ion affects force and fatigue. Identifying the activation pattern that prod uces the greatest force and least fatigue for each patient is, therefore, o f great importance. Mathematical models that predict muscle forces and fati gue produced by a wide range of stimulation patterns would facilitate the s earch for optimal patterns. Previously, we developed a mathematical isometr ic force model that successfully identified the stimulation patterns that p roduced the greatest forces from healthy subjects under nonfatigue and fati gue conditions. The present study introduces a four-parameter fatigue model , coupled with the force model that predicts the fatigue induced by differe nt stimulation patterns on different days during isometric contractions. Th is fatigue model accounted for 90% of the variability in forces produced by different fatigue tests. The predicted forces at the end of fatigue testin g differed from those observed by only 9%. This model demonstrates the pote ntial for predicting muscle fatigue in response to a wide range of stimulat ion patterns.