A new method for muscle fatigue assessment: Online model identification techniques

: The purpose of this study was to propose a method that allows extraction of the current muscle state under electrically induced fatigue. Methods : The triceps surae muscle of 5 subjects paralyzed by spinal cord injury was fatigued by intermittent electrical stimulation (5 × 5 trains at 30 H z ). Classical fatigue indices representing muscle contractile properties [peak twitch (Pt) and half‐relaxation time (HRT)] were assessed before and after each 5‐train series and were used to identify 2 relevant parameters ( F m , U r ) of a previously developed mathematical model using the Sigma‐Point Kalman Filter. Results : Pt declined significantly during the protocol, whereas HRT remained unchanged. Identification of the model parameters with experimental data yielded a model‐based fatigue assessment that gave a more stable evaluation of fatigue than classical parameters. Conclusions : This work reinforces clinical research by providing a tool that clinicians can use to monitor fatigue development during stimulation. Muscle Nerve 50: 556–563, 2014