A comparison of customized strategies to manage muscle fatigue in isometric artificially elicited muscle contractions for incomplete SCI subjects

Muscle fatigue due to functional electrical stimulation still prevents its widespread use as a gait rehabilitation tool for spinal cord injured subjects. Although there is an active research towards optimization of pulse parameters to delay muscle fatigue, changes in stimulated muscle's performance during repeated contractions due to fatigue have not been yet determined. In this work, a study conducted in two phases with a sample of incomplete spinal cord injured patients is presented. In the first phase, a fatigue protocol based on submaximal isometric contractions allowed to obtain an objective criterion for estimation of fatigue of knee muscles from initial changes in muscle performance. The criterion is incorporated in the fatigue protocol in the second phase of the study, to compare two novel customized fatigue management strategies. Results showed that knee flexor muscles develop less force and lower fatigue than extensor muscles. Muscle fatigue management strategies based on customized modulations of stimulation frequency are valid to delay muscle fatigue