Overground gait transitions are not sharp but involve gradually changing walk-run mixtures even over long distances

TL;DR

This study reveals that overground gait transitions are gradual, involving mixtures of walking and running over a broad speed range, and are governed by energy optimization principles, unlike the sharp transitions observed on treadmills.

Contribution

It demonstrates that overground gait transitions are not sharp but involve gradual mixtures, extending previous treadmill findings to real-world, long-distance locomotion scenarios.

Findings

Gait transition occurs over a broad speed range from 1.9 to 3.0 m/s.

People use mixtures of walking and running during transitions.

Energy optimality predicts the structure of gait mixtures.

Abstract

Humans typically walk at low speeds and run at higher speeds. Previous studies of transitions between walking and running were mostly on treadmills, but real-world locomotion allows more flexibility. Here, we study overground locomotion over long distances (800 m or 2400 m) under time constraints, simulating everyday scenarios like going to an appointment. Unlike on treadmills, participants can vary both speed and gait during this task. We find that gait transition in this overground task occurs over a broad `gait transition regime' spanning average speeds from 1.9 m/s to 3.0 m/s. In this regime, people use mixtures of walking and running: mostly walking at low average speeds (around 1.9 m/s) and mostly running at high average speeds (3.0 m/s); the walk vs run fraction gradually changes between these speed limits. Within any walk-run mixture, there is a speed gap between the walking and running. These gait mixtures and their specific structure are predicted by energy optimality. These findings extend earlier results from much shorter distance tasks, showing that similar energetic principles govern longer, more physically and cognitively demanding tasks. Overall, our results highlight the role of whole-task energy minimization including transients in shaping human locomotion.