Energetics of human locomotion near the walk–run transition speed

This study aimed to investigate the mechanical and metabolic effects of variable-speed locomotion involving repeated walk–run and run–walk transitions. Specifically, we assessed whether such transitions introduce an additional energetic cost and how they influence mechanical work and efficiency compared with steady-state walking and running. We hypothesized that accelerations during transitions would increase mechanical work and that the metabolic cost would exceed theoretical estimates based on constant-speed trials. Twenty-two male runners completed treadmill trials at constant speeds (walking and running) and under a variable speed protocol (VSP) involving cycles of acceleration and deceleration centred on each participant’s walk–run transition speed. Mechanical work was derived from three-dimensional motion capture data, and metabolic cost from indirect calorimetry. Apparent efficiency and energy recovery were also calculated. The measured metabolic cost of VSP was compared with an estimated value based on constant-speed walking and running trials. The VSP trials produced distinct mechanical and metabolic profiles, with values typically intermediate between walking and running. The 4.7% increase in VSP metabolic cost relative to the estimated value suggests that gait transitions impose an additional energetic overhead. Internal kinetic work during VSP resembled running, while the external work and the energy recovery laid between the two gaits.