Metabolic Cost Of Human Locomotion On Soft Terrain

BACKGROUND: Human locomotion on variable surface terrain (i.e., sand, snow, ice) provides unique physiological challenges. The evolution of tools such as skis, snowshoes, or ice skates has enabled humans to move across some of this terrain with greater economy (i.e., lower metabolic energy required to move a given distance). To date, there are no reports on the utilization of tools to improve human locomotion on soft sand terrain. PURPOSE: To determine which mode of human locomotion, foot (walking/running) or bicycling, is most economical for travel on sand. We hypothesized that bicycling would have a lower metabolic cost than foot across a range of speeds, thus resulting in greater economy. METHODS: Four adults with running and bicycling experience traversed a flat sand loop (200 m) while on foot or bicycle. While bicycling, participants rode a specialized bike equipped with oversized tires. Participants completed six sub-maximal exercise trials, three on foot (one walking speed and two running speeds at ~3, 4, 5mph) and three bicycling (~5, 6, 7mph). During all trials, participants wore a portable metabolic system that measured oxygen consumption (VO2). The difference between resting VO2 and steady state exercise VO2 for each trial were used to calculate a net VO2 which was then converted to metabolic energy (J). Metabolic energy for each trial was divided by distance covered and participant body mass to calculate economy (J/kg/m). The general effect of mode (i.e., foot vs. bicycle across all speeds) and the effect of mode at matched speed (i.e., foot vs. bicycle at 5mph) on economy were assessed using paired-samples t-tests (α-level = 0.05). RESULTS: Economy of travel was lower for bicycling compared to foot across the range of speeds (2.99 ± 0.33 vs. 4.81 ± 0.84 J/kg/m; p < 0.001) and at the matched speed of 5mph (3.06 ± 0.46 vs. 5.11 ± 0.56 J/kg/m; p = 0.01). CONCLUSION: Together, these data demonstrate that bicycling has greater economy than foot travel at any given speed on sand. This indicates that it is the superior mode of human locomotion when minimizing metabolic cost is a consideration. This research has implications for which mode of travel may be optimal for human powered exploration in desert environments. Research reported in this publication was supported in part by funding provided by the National Aeronautics and Space Administration (NASA), under award number 80NSSC20M0124, Michigan Space Grant Consortium (MSGC).