Understanding the Effects of High Intensity Treadmill Training on Corticomotor Excitability and Walking in Stroke Survivors

Stroke is a leading cause of adult disability, with gait deficits contributing significantly to functional limitations after stroke. One of the reasons for functional impairment after stroke is the decrease in neural drive, or the corticomotor excitability to the affected side of the lower limb muscles. The goal of this study was to understand the effects of a novel high intensity treadmill training (HITT) protocol on walking speeds and neural drive in individuals who had a stroke. Our sample consisted of three individuals who had a stroke and were able to walk for at least 10 minutes with- out assistance. This was a pilot study that was a part of a larger randomized controlled trial examining the effects of a noninvasive brain stimulation (NIBS) on treadmill training. All subjects participated in 12 sessions of treadmill training (40 minutes per session, three days a week for four weeks). Overground walking speed was examined throughout the four weeks of training, and corticomotor excitability was examined at baseline and after completion of training. Corti- comotor excitability was measured using non-invasive transcranial magnetic stimulation (TMS) of the lower limb motor cortex. At the end of four weeks post training, we noticed a decrease in motor evoked potentials (MEPs) elicited via TMS in the paretic tibialis anterior (TA) muscle. In addition, we noticed improvements in treadmill training speeds and overground walking speeds. This paradox may indicate a number of things—spinal cord excitability may be elicited more than the motor cortex (Martinez, Delivet-Mongrain, & Rossignol, 2012), or endurance training may be playing a role in excitability because of practice effects (Kumpulainen et al., 2014). This preliminary data brings questions that arise from the paradoxical phenomenon that HITT has on the neural drive and gait speed in stroke survivors. These results are promising and form the basis of investigating the effects of walking training on neural plasticity.