Walking is a complex task involving the coordination of multiple body segments over multiple cycles (steps) [1–3]. As one of the most practised of all motor skills , variability allows us to continuously construct adaptive coordination patterns as we move through the environment, resisting expected and unexpected perturbations that may occur causing instability . Studies of variability are thus central to understanding gait stability [7–9]. Control of speed during walking is a coordinated task driven by the interactions of the nervous and musculoskeletal systems and the environment . Motor tasks such as a step cycle are provided a window of optimal variability that enables accurate, stable completion of that task , despite internal and external perturbations.