The effect of random modulation of functional electrical stimulation parameters on muscle fatigue

Abstract

Abstract-Muscle contractions induced by functional electrical stimulation (FES) tend to result in rapid muscle fatigue, which greatly limits activities such as FES-assisted standing and walking. It was hypothesized that muscle fatigue caused by FES could be reduced by randomly modulating parameters of the electrical stimulus. Seven paraplegic subjects participated in this study. While subjects were seated, FES was applied to quadriceps and tibialis anterior muscles bilaterally using surface electrodes. The isometric force was measured, and the time for the force to drop by 3 dB (fatigue time) and the normalized force-time integral (FTI) were determined. Four different modes of FES were applied in random order: constant stimulation, randomized frequency (mean 40 Hz), randomized current amplitude, and randomized pulsewidth (mean 250 s). In randomized trials, stimulation parameters were stochastically modulated every 100 ms in a range of 15% using a uniform probability distribution. There was no significant difference between the fatigue time measurements for the four modes of stimulation. There was also no significant difference in the FTI measurements. Therefore, our particular method of stochastic modulation of the stimulation parameters, which involved moderate (15%) variations updated every 100 ms and centered around 40 Hz, appeared to have no effect on muscle fatigue. There was a strong correlation between maximum force measurements and stimulation order, which was not apparent in the fatigue time or FTI measurements. It was concluded that a 10-min rest period between stimulation trials was insufficient to allow full recovery of muscle strength.Index Terms-Functional electrical stimulation (FES), isometric contraction, muscle fatigue, spinal cord injury (SCI), stimulation frequency.

Matching initial torque with different stimulation parameters influences skeletal muscle fatigue

“…Further studies need to be conducted that include longer fatigue tests and modulation of parameters (e.g., pulse waveforms, frequency, duration, or amplitude) to identify strategies that can reduce levels of fatigue. While some of this work has been done with varying degrees of success [10,[21][22], electrical stimulation has great potential for rehabilitation if the degree of muscle fatigue can be reduced.…”

Identification of electrically stimulated muscle models of stroke patients

“…For the TR, Staircase and FRN tests, 10 trials were performed, however, in the case of the PRMS test, only four trials were carried out as it was evident that the fit rate was poor. Between every two tests there was a rest period of at least 10 min in order to eliminate fatigue (Graham, Thrasher, & Popovic, 2006), and the order of identification tests was also randomized to minimize the effect of subject memory or acclimatization increasing the subject's involuntary response.…”

Minimizing muscle fatigue through optimization of electrical stimulation parameters

“…Consequently, our control strategy for each participant is sufficiently consistent and thus suitable for repetitive clinical applications. However, since muscle training can affect FES performance, [33] it is expected that muscle training will change the proposed strategy for modulating (PA,PD) pairing, and thus the present experimental protocol should be repeated at regular intervals following prolonged FES training.…”

“…[18,20,[33][34][35][36][37] A drop of MT from its maximum (100%) to 70.7% (3 dB) was chosen since, in the control engineering literature, when the system output drops by 3 dB, its performance is considered altered. [33] This value has been used in other studies. [18,38] Nevertheless, other researchers have also used a threshold of 50%.…”