Why change gaits? Dynamics of the walkun transition.

TLDR

Humans switch from walking to running at a specific speed, prompting investigation into the underlying cause. The study proposes that gait transitions behave like nonequilibrium phase transitions between attractors. Experiment 1 varied treadmill speed to observe walking and running, while Experiment 2 independently manipulated speed, stride length, and frequency, showing that the transition occurs at a constant speed near the equal‑energy separatrix. The transition occurs at the equal‑energy separatrix, accompanied by predicted shifts in stride length and frequency, a qualitative reorganization of leg segment phasing, a sudden jump and enhanced fluctuations in relative phase, hysteresis, and overall consistency with a dynamic theory in which preferred gaits are stable phase relationships minimizing energy and transitions involve loss of stability and reduced energetic costs.

Abstract

Why do humans switch from walking to running at a particular speed? It is proposed that gait transitions behave like nonequilibrium phase transitions between attractors. Experiment 1 examined walking and running on a treadmill while speed was varied. The transition occurred at the equal-energy separatrix between gaits, with predicted shifts in stride length and frequency, a qualitative reorganization in the relative phasing of segments within a leg, a sudden jump in relative phase, enhanced fluctuations in relative phase, and hysteresis. Experiment 2 dissociated speed, frequency, and stride length to show that the transition occurred at a constant speed near the energy separatrix. Results are consistent with a dynamic theory of locomotion in which preferred gaits are characterized by stable phase relationships and minimum energy expenditure, and gait transitions by a loss of stability and the reduction of energetic costs.