Fig. 2. Mean ± s.d. of the metabolic cost of transport is shown as a function of speed of progression for all the ice skates used in the present study. Units of measure were converted from ml O₂ to J, according to the respiratory exchange ratio (see text for further details). Iso-metabolic power curves (cost X speed=constant) are represented by the two hyperbolae. Data referring to walking, running and riding a racing bicycle on firm terrain are shown for the sake of comparison and were taken from previous publications (Cavagna and Kaneko, 1977; Capelli et al., 1998). The cost of walking on snow at 0.67 m s^–1 is also shown in respect to the footprint depth, reported in cm, as measured by Pandolf et al. (Pandolf et al., 1976). In relatively recent competitions, the introduction of klapskates has allowed 5% faster speeds for energy cost values similar to those reported here for modern ice skates.