Minimizing muscle fatigue through optimization of electrical stimulation parameters

Abstract

Rapid onset of muscle fatigue in response to electrical stimulation is a major challenge when designing a neuroprosthesis. This study aimed to introduce a decision-making algorithm to optimize pulse amplitude and pulse duration, for current regulated electrical stimulators, to attain a target joint torque level while minimizing muscle fatigue. We measured ankle torque produced by different pairs of pulse amplitude and pulse duration applied to the plantar-flexors. In each session, we measured the maximum generated torque and calculated muscle fatigue (fatigue time and torque-time integral). Then, we determined the pulse amplitude and pulse duration pair that generated a target level of torque while minimizing muscle fatigue. High bilateral symmetry and day-to-day repeatability was observed for the torque time-series between the left and right plantar-flexors of each participant (median correlation coefficient = 0.95). Compared to the average fatigue obtained by various pulse amplitude and pulse duration pairs for a given level of torque, delivering pulses with the optimal pair reduced fatigue on average by 22.5% according to fatigue time and 6.6% according to torque-time integral. We created an empirical model describing how pulse amplitude and pulse duration can be modulated to generate specific levels of plantar-flexion torque with minimum muscle fatigue.