Afferent electrical stimulation during cycling improves spinal processing of sensorimotor function after incomplete spinal cord injury.

Abstract

Appropriate afferent feedback delivery during the execution of motor tasks is important for rehabilitation after incomplete spinal cord injury (iSCI). However, during leg-cycling therapy, the plantar afferent feedback is minimal. We hypothesize that the augmentation of sensory input by combining cycling with a locomotor-like stimulation of plantar cutaneous innervations (ES-cycling), might help to restore proper spinal processing of sensorimotor function. Thirteen non-injured subjects and 10 subjects with iSCI performed 10 minutes of cycling and, on another session, of ES-cycling. To assess spinal processing of sensorimotor function, soleus H-reflex response was tested following a conditioning plantar electrical stimulation applied at 25-100 ms inter-stimulus intervals (ISI's), measured before and after the execution of the tasks. Before tasks execution, the conditioned H-reflex response was modulated in non-injured subjects, and absent in subjects with iSCI; after cycling, modulation profiles were unchanged. However, after ES-cycling a significant increase in H-reflex excitability was observed in the non-injured group at 100 ms ISI (p < 0.05), and in the iSCI group between 50-75 ms ISI (p < 0.001). The loss of reflex modulation in subjects with iSCI suggests reduced spinal processing of sensorimotor function. Reflex modulation recovery after ES-cycling may indicate the partial reactivation of these mechanisms.