Energy cost and efficiency of ski mountaineering. A laboratory study.

The purpose of this study is to estimate the energy cost of ski mountaineering at different speeds under laboratory conditions.By using roller skis on a motorized treadmill we have estimated the energy cost and biomechanics parameters of ski mountaineering as a function of climbing speed at the gradient of 21\%.The metabolic energy spent for unit mass and distance, C, shows a broad minimum of about 10.6±0.2 J kg-1m-1 at roughly 3.5 km h-1. In addition we find a size-dependent effect: tall subjects spend less metabolic energy for unit mass and distance than small subjects at the same speed.The value of C measured in laboratory agrees with that obtained in the field at the preferred speed. This shows that skiers self select a speed that minimizes their metabolic cost. The dependence of C on the subject's size is explained by a simple model of the skier's dynamics. In addition we have calculated the ratio between mechanical work and metabolic energy, which may give some hints on the efficiency as a function of the speed. It turns out that efficiency increases with the speed up to a maximum located at around 4.5 km/h.