Modulation of corticospinal input to the legs by arm and leg cycling in people with incomplete spinal cord injury

Abstract

The spinal cervico-lumbar interaction during rhythmic movements in humans has recently been studied; however, the role of arm movements in modulating the corticospinal drive to the legs is not well understood. The goals of this study were to investigate the effect of active rhythmic arm movements on the corticospinal drive to the legs () and assess the effect of simultaneous arm and leg training on the corticospinal pathway after incomplete spinal cord injury (iSCI) ( 2). In , neurologically intact (NI) participants or participants with iSCI performed combinations of stationary and rhythmic cycling of the arms and legs while motor evoked potentials (MEPs) were recorded from the vastus lateralis (VL) muscle. In the NI group, arm cycling alone could facilitate the VL MEP amplitude, suggesting that dynamic arm movements strongly modulate the corticospinal pathway to the legs. No significant difference in VL MEP between conditions was found in participants with iSCI. In, participants with iSCI underwent 12 wk of electrical stimulation-assisted cycling training: one group performed simultaneous arm and leg (A&L) cycling and the other legs-only cycling. MEPs in the tibialis anterior (TA) muscle were compared before and after training. After training, only the A&L group had a significantly larger TA MEP, suggesting increased excitability in the corticospinal pathway. The findings demonstrate the importance of arm movements in modulating the corticospinal drive to the legs and suggest that active engagement of the arms in lower limb rehabilitation may produce better neural regulation and restoration of function. This study aimed to demonstrate the importance of arm movements in modulating the corticospinal drive to the legs. It provides direct evidence in humans that active movement of the arms could facilitate corticospinal transmission to the legs and, for the first time, shows that facilitation is absent after spinal cord injury. Active engagement of the arms in lower limb rehabilitation increased the excitability of the corticospinal pathway and may produce more effective improvement in leg function.

Simultaneous Cervical and Lumbar Spinal Cord Stimulation Induces Facilitation of Both Spinal and Corticospinal Circuitry in Humans

“…However, this facilitation was not present during arm cycling for individuals with incomplete SCI prior to A&L cycling training (Zhou et al, 2017). Excitingly, 12 weeks of A&L cycling training reengaged these connections by significantly increasing the amplitude of the motor evoked potential (MEP) in the tibialis anterior muscle compared to baseline levels prior to the intervention (Zhou et al, 2017). Furthermore, disruptions in cervico-lumbar connectivity, which are noted after both incomplete SCI and chronic stroke, can be reduced by the simultaneous A&L cycling paradigm (Klarner et al, 2016b;Zhou et al, 2018b).…”

“…The torso was restrained using a seat belt, and the experimental arm (left) was secured in a fixed pronated position using straps into a secure brace, embedded with a force sensor (Neurolog, Hertfordshire, United Kingdom). The left arm was chosen to be comparable to previous investigations from the same laboratory (Zhou et al, 2017(Zhou et al, , 2018b. The effect of leg cycling on upper limb reflex responses between the right and left limbs, and the relative difference between experimental conditions is expected to be similar regardless of which arm is used (Zehr et al, 2007;Nakajima et al, 2013).…”

“…Corticospinal projections to spinal motor neurons are generally facilitated during cycling in neurologically intact individuals. However, this facilitation was not present during arm cycling for individuals with incomplete SCI prior to A&L cycling training (Zhou et al, 2017). Excitingly, 12 weeks of A&L cycling training reengaged these connections by significantly increasing the amplitude of the motor evoked potential (MEP) in the tibialis anterior muscle compared to baseline levels prior to the intervention (Zhou et al, 2017).…”

A 12-Week Cycling Training Regimen Improves Upper Limb Functions in People With Parkinson’s Disease

“…This would suggest that functional changes in corticospinal pathways may occur at multiple levels, not only at those directly involved in generating and controlling the limbs performing the movements. In support of such mechanisms are the findings of a work performed by Zhou et al (2017) that demonstrate changes in the motor-evoked potentials in the lower limb in neurologically intact individuals and patients with incomplete spinal cord injury following arm cycling alone or simultaneous arm and leg cycling, respectively. Our study adds to this body of knowledge, by providing evidence that AET can improve the synergistic action of an agonist and antagonist neuromuscular networks in PD.…”

Global Corticospinal Excitability as Assessed in A Non-Exercised Upper Limb Muscle Compared Between Concentric and Eccentric Modes of Leg Cycling

“…This is supported by the work of Zehr and colleagues, who showed that motor evoked potentials (MEPs) elicited in non-exercising arm muscles are facilitated during submaximal leg cycling 5 . Similarly, during low-intensity cycling using the arms, MEPs measured in the non-exercising vastus lateralis (leg) muscle also increased 6 . Taken together, these findings indicate that as facilitation was observed in non-exercising muscles, exercise contributes to increasing a state of ‘global corticospinal excitability’ (CSE).…”