Data from: The metabolic cost of changing walking speeds is significant, implies lower optimal speeds for shorter distances, and increases daily energy estimates

Humans do not generally walk at constant speed, except perhaps on a
treadmill. Normal walking involves starting, stopping and changing speeds,
in addition to roughly steady locomotion. Here, we measure the metabolic
energy cost of walking when changing speed. Subjects (healthy adults)
walked with oscillating speeds on a constant-speed treadmill, alternating
between walking slower and faster than the treadmill belt, moving back and
forth in the laboratory frame. The metabolic rate for oscillating-speed
walking was significantly higher than that for constant-speed walking
(6–20% cost increase for ±0.13–0.27 m s−1 speed fluctuations). The
metabolic rate increase was correlated with two models: a model based on
kinetic energy fluctuations and an inverted pendulum walking model,
optimized for oscillating-speed constraints. The cost of changing speeds
may have behavioural implications: we predicted that the energy-optimal
walking speed is lower for shorter distances. We measured preferred human
walking speeds for different walking distances and found people preferred
lower walking speeds for shorter distances as predicted. Further,
analysing published daily walking-bout distributions, we estimate that the
cost of changing speeds is 4–8% of daily walking energy budget.