Corticospinal function does not predict stride-to-stride gait dynamics in older adults

Introduction: Ageing is associated with impaired gait adaptability, which leads to an increased fall risk in older adults. The study of the temporal structure of stride-to-stride fluctuations may help mitigate these inherent risks, as it has been proposed as a marker of locomotor functionality and motor control. However, the underlying mechanisms responsible for the progressive deterioration of stride-to-stride fluctuations in older adults are yet to be fully unravelled. Recent research suggests several central and peripheral factors can influence the walking adaptation process with the corticospinal tract playing a key role in motor control during gait. Thus, the purpose of this study was to investigate whether lower-leg corticospinal drive significantly explains the temporal structure of gait stride-to-stride fluctuations. Methods: Thirty-four older adults underwent transcranial magnetic stimulation (TMS) assessments of the tibialis anterior in one experimental session, where corticospinal excitability (CSE), silent period duration (SP), and short-interval intracortical inhibition (SICI) were quantified. Immediately after the TMS intervention, they also performed a 12-min treadmill walking trial at preferred walking speed, during which inter-stride intervals were extracted and analysed using detrended fluctuation analysis to obtain the fractal scaling exponent (αISIs). Multiple linear regression analysis was used to examine whether CSE, SP and SICI predicted αISIs. Discussion: These findings suggest that gait adaptability does not seem to be explained by corticospinal function, likely emerging from distributed, multilevel neural control processes involving spinal, supraspinal, and peripheral mechanisms rather than corticospinal contributions alone.