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.
Highlights
Muscle atrophy, and the consequent alteration of the proportion of slow-twitch type I motor units (MU) to fast-fatigable type IIB MU, are negative neuromuscular sequelae secondary to spinal cord injury (SCI) [1, 2]
The need for further in-depth clinical trials 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 functional electrical stimulation (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
Summary
The consequent alteration of the proportion of slow-twitch type I motor units (MU) to fast-fatigable type IIB (with low aerobic-oxidative enzymatic capacity) MU, are negative neuromuscular sequelae secondary to spinal cord injury (SCI) [1, 2]. The power output and exercise capacity of such muscles are diminished due to inactivity and unloading concomitant with post-SCI wheelchair confinement [4]. This is clearly evident in the decline of force-generating capacity of muscle (i.e. specific tension (NÁcm-2)) [5], due to the problem of muscle fatigue in individuals with neurological disorders [6]. There is on-going research interest into developing effective strategies to counteract the effects of rapid muscle fatigue, during neuromuscular electrical stimulation for therapeutic and functional interventions in persons with neurological impairment, SCI [8]. Rapid 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. The review sought to synthesize the effectiveness of these strategies for persons with SCI in order to establish their functional impacts and clinical relevance
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