Strategies for Rapid Muscle Fatigue Reduction during FES Exercise in Individuals with Spinal Cord Injury: A Systematic Review

Abstract

BackgroundRapid muscle fatigue during functional electrical stimulation (FES)-evoked muscle contractions in individuals with spinal cord injury (SCI) is a significant limitation to attaining health benefits of FES-exercise. Delaying the onset of muscle fatigue is often cited as an important goal linked to FES clinical efficacy. Although the basic concept of fatigue-resistance has a long history, recent advances in biomedical engineering, physiotherapy and clinical exercise science have achieved improved clinical benefits, especially for reducing muscle fatigue during FES-exercise. This review evaluated the methodological quality of strategies underlying muscle fatigue-resistance that have been used to optimize FES therapeutic approaches. The review also sought to synthesize the effectiveness of these strategies for persons with SCI in order to establish their functional impacts and clinical relevance.MethodsPublished scientific literature pertaining to the reduction of FES-induced muscle fatigue was identified through searches of the following databases: Science Direct, Medline, IEEE Xplore, SpringerLink, PubMed and Nature, from the earliest returned record until June 2015. Titles and abstracts were screened to obtain 35 studies that met the inclusion criteria for this systematic review.ResultsFollowing the evaluation of methodological quality (mean (SD), 50 (6) %) of the reviewed studies using the Downs and Black scale, the largest treatment effects reported to reduce muscle fatigue mainly investigated isometric contractions of limited functional and clinical relevance (n = 28). Some investigations (n = 13) lacked randomisation, while others were characterised by small sample sizes with low statistical power. Nevertheless, the clinical significance of emerging trends to improve fatigue-resistance during FES included (i) optimizing electrode positioning, (ii) fine-tuning of stimulation patterns and other FES parameters, (iii) adjustments to the mode and frequency of exercise training, and (iv) biofeedback-assisted FES-exercise to promote selective recruitment of fatigue-resistant motor units.ConclusionAlthough the need for further in-depth clinical trials (especially RCTs) was clearly warranted to establish external validity of outcomes, current evidence was sufficient to support the validity of certain techniques for rapid fatigue-reduction in order to promote FES therapy as an integral part of SCI rehabilitation. It is anticipated that this information will be valuable to clinicians and other allied health professionals administering FES as a treatment option in rehabilitation and aid the development of effective rehabilitation interventions.

Neuromuscular fatigue after low‐ and medium‐frequency electrical stimulation in healthy adults

“…It will be important to conduct further studies that compare different stimulation characteristics, so as to better understand this process. Changes in stimulation parameters (pulse frequency, width, and amplitude) have been suggested as a fundamental strategy to mimic natural motor unit recruitment—that is, recruitment of additional motor units when the fibers initially recruited become fatigued and, consequently, delay muscle fatigue . For example, comparing conventional stimulation with high‐frequency currents could produce different fatigue origins due to potentially different recruitment patterns .…”

An investigation into the effect of electrode type and stimulation parameters on FES-induced dynamic movement in the presence of muscle fatigue for a voltage-controlled stimulator

“…The use of hybrid exoskeletons, which are the focus of this work have already been shown capable of improving FES precision [9] thus the main goal with regards to FES for this work is towards reducing the FES-induced fatigue. It is also in this area that the most gaps remain [35].…”

Effects of pulse duration on muscle fatigue during electrical stimulation inducing moderate‐level contraction

“…These systems are used by individuals with paralysis from spinal cord injury and stroke and also for neuromuscular disorders . Rapid onset of muscle fatigue and discomfort, however, are major obstacles preventing the effective use of these systems . Muscle force production during NMES is dependent on the stimulation parameters of pulse duration, amplitude, and frequency .…”

“…2,3 Rapid onset of muscle fatigue and discomfort, however, are major obstacles preventing the effective use of these systems. 4,5 Muscle force production during NMES is dependent on the stimulation parameters of pulse duration, amplitude, and frequency. 6 Increasing either pulse duration or amplitude will increase force production through recruitment of additional motor units.…”

“…[9][10][11] Typical functional electrical stimulation (FES) systems use pulse durations of 200-400 ls and frequencies of 30-50 HZ. 5 Many studies have investigated variations in stimulation frequency over time to slow the progression of fatigue. 6 Although starting with initially high frequencies can exacerbate fatigue, 12,13 slowly increasing frequency from 20 to 40 HZ during the course of a fatigue task resulted in prolonged force output over time.…”