Optimizing Reduction in Muscle Fatigue in FES Using Stimulation Patterns

Introduction: During functional electrical stimulation (FES) the onset of muscle fatigue limits the treatment and rehabilitation of patients. In previous work, variable frequency trains (VFT) have been suggested to take advantage of a tension enhancement property in muscle. The varying of other parameters in stimulation trains, such as amplitude, was found to be lacking in literature. Here, the effect of various VFT and variable amplitude train (VAT) configurations on muscle fatigue were investigated. Methods: Ten different stimulation trains were tested in fatigue trials in the left tibialis anterior of 21 healthy rats. The state of the muscle was measured before and after each trial. Results: The VFT starting with two high frequency pulses caused significantly less fatigue (p < 0:001). The force-time integrals of the VAT starting with 8 high amplitude pulses are significantly larger (p < 0:05). Conclusion: The results of the VFT agree with previous studies; VFTs with two high frequency pulses are the optimal stimulation patterns in reducing muscle fatigue. Compared to conventional trains, VATs starting with 8 high amplitude pulses had a beneficial influence on muscle fatigue. The opposite pattern, a VAT ending with 8 high amplitude pulses produced a significantly larger force-time integral. Although a small significant difference was established in muscle fatigue for these VAT conditions, VFTs with two high frequency pulses performed better. A combination of amplitude and frequency variation should be explored in further research