Altered cutaneous reflexes to non-noxious stimuli in the triceps surae of people with chronic incomplete spinal cord injury

Following spinal cord injury (SCI), task-dependent modulation of spinal reflexes is often impaired. To gain insight into the state of the spinal interneuronal pathways following injury, we studied the amplitude modulation of triceps surae cutaneous reflexes to non-noxious stimuli during standing and early-to-mid stance phase of walking in participants with and without chronic incomplete SCI. Reflex eliciting nerve stimulation was delivered to the superficial peroneal, sural, and distal tibial nerves about the ankle. Reflexes were analyzed in the short (SLR, 50–80 ms poststimulation onset) and the medium (MLR, 80–120 ms) latency response windows. Furthermore, the relation between cutaneous and H-reflexes was also examined during standing. In participants without injuries the soleus SLR was modulated task dependently with nerve specificity, and the soleus and medial gastrocnemius MLRs were modulated task dependently. In contrast, participants with SCI, no task-dependent or nerve-specific modulation of triceps cutaneous reflexes was observed. The triceps surae cutaneous and H-reflexes were not correlated in either group (r = 0.01–0.37). The presence of cutaneous reflexes but the absence of significant amplitude modulation may suggest impaired function of spinal interneuronal pathways in this population. The lack of correlation between the cutaneous and H-reflexes may suggest that interneurons that are involved in H-reflex modulation and cutaneous reflex modulation do not receive common input, or the impact of the common input is outweighed by other input. Present findings highlight the importance of examining multiple spinal reflexes to better understanding spinal interneuronal pathways that affect motor control in people after SCI. NEW & NOTEWORTHY This study examined modulation of the triceps surae cutaneous reflexes during standing and walking and the relationship between cutaneous and H-reflexes in people with chronic incomplete spinal cord injury (SCI). In people with SCI, the normal task-dependent, nerve-specific modulation of triceps cutaneous reflexes was missing. Cutaneous and H-reflexes were not correlated. Together with other spinal reflexes, cutaneous reflexes may serve as important biomarkers for the state of spinal interneuronal pathways.