Perceived task expectations and the walk-run gait transition

This study examined the effect of expected task duration on the walk – run transition speed in human terrestrial locomotion and the hypothesis that the transition is made to minimize metabolic energy expenditure. Twelve healthy male participants engaged in treadmill locomotion trials lasting 50 s, 100 s, 5 min, 10 min, and 30 min. Speed was increased in 10 steps, every 0.1 m·s starting at 1.4 m·s, and the preferred walk – run transition speed was recorded. Participants also walked and ran at 40, 55, 70, 85, 100, 115, and 130% of the 30min preferred transition speed while oxygen consumption data were recorded. The metabolically optimal transition speed was then determined for extended walking and running. Participants moved on the treadmill at roughly 90% of the metabolically optimal transition speed in trials lasting 30 s, 3 min, 15 min, and 40 min. Running was more metabolically costly than walking at this speed. Participants were informed regarding trial duration prior to testing in the 30 s, 3 min, and 15 min conditions, but not in the 40-min condition. Both central and peripheral ratings of perceived exertion (RPE) were obtained at all speeds. The preferred walk – run transition speed decreased with increasing task duration and the preferred transition speed for each duration condition occurred prior to the metabolically optimal transition speed. Central RPE values increased across the walk – run transition while peripheral RPE values decreased. With increasing task duration, participants preferred running to walking at approximately 90% of the metabolically optimal transition speed. Moreover, participants experienced difficulty selecting the appropriate gait when the task duration was ambiguous. These results provide evidence to refute the hypothesis that the minimization of metabolic energy expenditure is the primary trigger for the transition between walking and running. Rather, the transition is made to reduce peripheral sensations of effort associated with fast walking. Furthermore, task-relevant information influences the decision whether to walk or run. It is concluded that perceptions about the task constraint create an informational boundary for a hierarchical array of physical gait triggers.