The effect of age on neuromechanical responses to electrical stimulation of superficial peroneal nerve during walking




Brodie, Ryan

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In the healthy young, stimulation of superficial peroneal nerve (SPn) cutaneous afferents at the ankle during walking has been shown to elicit functionally relevant neural and mechanical responses that contribute to obstacle avoidance during swing and have been referred to as stumble corrective responses. However, specific age-related differences in the stumble corrective response induced by electrically evoked cutaneous stimulation have yet to be determined. As a confounding contributor to age related changes in dynamic stability during locomotion, neural and mechanical changes in the stumble corrective response may result in a decreased ability to recover from a destabilizing incident and provide key markers of neuromuscular decline. Therefore the purpose of this study was to compare age-dependent differences in responses to electrically evoked stimulation of the superficial peroneal nerve at the ankle during walking in healthy young and elderly groups. Electromyograms (EMG) of the tibialis anterior (TA), soleus (Sol), medial gastrocnemius (MG), biceps femoris (BF) and vastus lateralis (VL) were recorded along with gait kinematics including joint displacement and angular velocity at the ankle and knee as well as toe clearance relative to the walking surface. Overall, the stumble corrective response was preserved in the elderly as evident by significant responses in kinematics and muscle activity that were similar in sign and phase to those seen in the healthy young. However, the magnitude of the kinematic responses and resulting toe clearance in older adults were significantly smaller than in the young. Further, during the swing phase of unstimulated walking cycles, there were reduced knee flexion, plantarflexion and toe clearance in the elderly with corresponding differences in muscle activity. Therefore, smaller kinematic responses to stimulation, in the elderly, superimposed on a different undisturbed gait profile, resulting in reduced toe clearance, reflects early degradation of the stumble corrective response. This early degradation is likely a prodromal sign of increased fall risk. This supports the potential use of cutaneous reflexes in quantifying degradation of neuromuscular control and its contribution to fall risk.



gait, locomotion, biomechanics, neuroscience, motor control, ageing, reflex, cutaneous