Effect of cervicolumbar coupling on spinal reflexes during cycling after incomplete spinal cord injury

Abstract

Spinal networks in the cervical and lumbar cord are actively coupled during locomotion to coordinate arm and leg activity. The goals of this project were to investigate the intersegmental cervico-lumbar connectivity during cycling after incomplete spinal cord injury (iSCI), and assess the effect of rehabilitation training on improving reflex modulation mediated by cervico-lumbar pathways. Two studies were conducted. In the first, 22 neurologically intact (NI) people and 10 people with chronic iSCI were recruited. The change in H-reflex amplitude in flexor carpi radialis (FCR) during leg cycling and H-reflex amplitude in soleus (SOL) during arm cycling were investigated. In the second study, two groups of participants with chronic iSCI underwent 12 weeks of cycling training: one performed combined arm and leg cycling (A&L) and the other legs only cycling (Leg). The effect of training paradigm on the amplitude of the SOL H-reflex was assessed. Significant reduction in the amplitude of both FCR and SOL H-reflexes during dynamic cycling of the opposite limbs was found in NI participants, but not in participants with iSCI. Nonetheless, there was a significant reduction in the SOL H-reflex during dynamic arm cycling in iSCI participants after training. Substantial improvements in SOL H-reflex properties were found in the A&L group after training. The results demonstrate that cervico-lumbar modulation during rhythmic movements is disrupted in people with chronic iSCI; however, this modulation is restored after cycling training. Furthermore, involvement of the arms simultaneously with the legs during training may better regulate the leg spinal reflexes.

Effects of neuromuscular electrical stimulation and voluntary commands on the spinal reflex excitability of remote limb muscles

“…In rehabilitation after spinal cord injury, significantly larger improvements of walking function and the cervicolumbar connectivity were found in the training group that included combined arm and leg cycling compared to the group that trained using only leg cycling (Zhou et al 2018a, b). These studies recommended active use of arm involvement during training to maximize improvements of walking function, which is directly aligned with our current study findings.…”

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

“…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).…”

“…The 180 • position of the left leg (i.e., 12 o'clock) was chosen as the phase of the leg during which both H-reflexes and MEPs are evoked for both the leg static and cycling conditions. This placement of the leg was chosen based on previous studies indicating that the 180 • leg position produces both peak muscle activity and the largest inhibition of the FCR H-reflex (Zhou et al, 2017(Zhou et al, , 2018b. Therefore, the positions of the left and right leg were held constant at 180 and 0 • , respectively, during static trials (Figure 2A).…”

“…Coupling between the arms and legs in humans has been demonstrated by the suppression of H-reflexes evoked in one limb by rhythmic movements of the remote limbs (Ferris et al, 2006;Hundza and Zehr, 2009;Zhou et al, 2018b). Moreover, engaging cervico-lumbar connections with simultaneous arm and leg (A&L) cycling training has been shown to improve walking after both chronic incomplete SCI (Zhou et al, 2018a) and stroke (Klarner et al, 2016a,b).…”

“…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). Presynaptic inhibition of Ia afferent terminals (premotorneuronal level) is thought to exert such an effect (Gossard, 1996;Frigon et al, 2004;Nakajima et al, 2013).…”