A scoping review of the contralateral effects of unilateral peripheral stimulation on neuromuscular function

Abstract

It is known that resistance exercise using one limb can affect motor function of both the exercised limb and the unexercised contralateral limb, a phenomenon termed cross-education. It has been suggested that cross-education has clinical implications, e.g. in rehabilitation for orthopaedic conditions or post-stroke paresis. Much of the research on the contralateral effect of unilateral intervention on motor output is based on voluntary exercise. This scoping review aimed to map the characteristics of current literature on the cross-education caused by three most frequently utilised peripheral neuromuscular stimulation modalities in this context: electrical stimulation, mechanical vibration and percutaneous needling, that may direct future research and translate to clinical practice. A systematic search of relevant databases (Ebsco, ProQuest, PubMed, Scopus, Web of Science) through to the end of 2020 was conducted following the PRISMA Extension for Scoping Review. Empirical studies on human participants that applied a unilateral peripheral neuromuscular stimulation and assessed neuromuscular function of the stimulated and/or the unstimulated side were selected. By reading the full text, the demographic characteristics, context, design, methods and major findings of the studies were synthesised. The results found that 83 studies were eligible for the review, with the majority (53) utilised electrical stimulation whilst those applied vibration (18) or needling (12) were emerging. Although the contralateral effects appeared to be robust, only 31 studies claimed to be in the context of cross-education, and 25 investigated on clinical patients. The underlying mechanism for the contralateral effects induced by unilateral peripheral stimulation remains unclear. The findings suggest a need to enhance the awareness of cross-education caused by peripheral stimulation, to help improve the translation of theoretical concepts to clinical practice, and aid in developing well-designed clinical trials to determine the efficacy of cross-education therapies.

Influence of One Hour versus Two Hours of Daily Static Stretching for Six Weeks Using a Calf-Muscle-Stretching Orthosis on Maximal Strength

“…The measured contralateral force transfer can also be seen as confirmation of the inclusion of neuronal aspects in the stretching-induced MSt increases. Zhou et al [ 29 ] referred to different methods of peripheral stimulation, e.g., electrical stimulation or vibration training to induce cross-educational effects; however, the underlying mechanisms remain unclear. Based on the current literature, the authors hypothesize that peripheral sensory inputs might play an important role in inducing contralateral force transfer effects.…”

“…Since neither imaging techniques (such as sonography or magnetic resonance imaging) were used to assess muscle hypertrophy, nor were EMG measurements conducted to quantify changes in neuronal innervation, the physiological factors of the increased MSt, as well as the cross-education effects, remain unclear. As Manca et al [ 50 ] highlighted a variety of possible explanations and Zhou et al [ 29 ] referred to the need for clarification regarding the underlying mechanisms of contralateral effects due to unilateral peripheral stimulation, further studies should include additional measuring procedures to gain more insights.…”

“…Cross-education effects are known from unilateral strength training [ 25 , 26 , 27 ]. Zhou [ 28 ] and Zhou et al [ 29 ] suggested that adaptations in motor learning are a preferred explanation of cross-education effects by showing that the electrical stimulation on one leg results in strength increases in the contralateral leg. The authors hypothesized that the cross-training effects could be attributed to afferent modulations.…”

Sex differences in stretch-induced hypertrophy, maximal strength and flexibility gains

“…These studies showed that long duration static stretching sessions implemented for 6 weeks resulted in moderate to large magnitude MSt increases of 14.2%-22.3% (d = 0.51-0.91), increases in MTh and ROM of 15.3% (d = 0.84) and 13.2%-27.3% (d = 0.47-0.87) dependent on used knee joint angle, respectively (Warneke et al, 2022b;Warneke et al, 2022c). Interestingly, previous studies also showed significant cross-education effects in response to stretching interventions of up to 12 weeks regarding MSt (Nelson et al, 2012;Warneke et al, 2022b;Warneke et al, 2022c), which might be attributed to neuronal adaptations induced by increased activity of stretch reflex afferents (Zhou, 2000;Zhou et al, 2022).…”

“…The contralateral force transfer is well known from strength training routines (Lee and Carroll, 2007;Manca et al, 2021). An explanatory approach of Zhou (2000Zhou ( , 2022 attributes increases in the contralateral leg with afferent signals induced by different training routines, which could be present without a central innervation of the muscle by voluntary contraction. This may be of an importance because no voluntary contraction can be assumed in passive stretch.…”