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.人类通常不会以恒定速度行走，除非在跑步机（treadmill）上进行运动。正常行走过程除了大致稳定的移动状态外，还包含启动、停止以及速度变化环节。本研究中，我们测量了变速行走时的代谢能耗。实验受试者为健康成年人，他们在恒速跑步机上以振荡变速模式行走：交替以慢于、快于跑步机传送带的速度行进，在实验室坐标系中往复位移。变速行走的代谢率显著高于恒速行走（当速度波动幅度为±0.13~0.27 m·s⁻¹时，能耗增加6%~20%）。代谢率的升高与两类模型存在相关性：一类基于动能波动的模型，另一类是针对变速约束优化的倒立摆行走模型。变速行走的能耗可能具有行为学层面的启示意义：我们预测，短距离行走时的能量最优速度更低。我们测量了不同行走距离下人类的偏好行走速度，结果发现受试者确实如预测那般，在短距离行走时选择更低的速度。此外，通过分析已发表的每日行走回合分布数据，我们估算得出，变速行走的能耗占人类每日行走总能耗预算的4%~8%。