Metabolically Optimal Gait Transitions in Cross-Country Skate Skiing

Abstract

With increasing speeds of locomotion, animals change their gait pattern to minimize metabolic cost. For ex- ample, a horse will walk at low speeds, trot at intermediate speeds and gallop at high speeds [1]. Likewise, cross-country skiers use the 2-skate technique at slow speeds, switch to the 1-skate technique at intermediate speeds, but then, in contrast to everything known about locomotion in humans and animals, they revert back to the previously rejected 2-skate technique at very high speeds of locomotion. This pattern of gait transitions suggests that the metabolic efficiency curves for 1-skate and 2-skate skiing intersect twice, rather than just once as they do for human walking and running. The purpose of this study was to test if the metabolic efficiency curves of 1-skate and 2-skate skiing intersect twice, and if so, find an explanation for this surprising result. Eight nationally competitive skiers were tested on a roller ski treadmill. Subjects were asked to ski at speeds of 6-33km/h at 3km/h increments, once with the 1-skate technique and once with the 2-skate technique. Oxygen consumption and 3d kinematics were recorded continuously. We found that the metabolic efficiency curves intersected twice. We also found that pole contact time and distance was much shorter per stride when using the 1-skate technique, especially at very low and very high speeds.