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Fig. 3. The three-colour (black, light grey, dark grey) curves represent the
maximum speed/distance relationships calculated for constant metabolic cost
for each skate model. Data for klapskates were calculated assuming 5% faster
speeds. The broken line reports values for running and is shown as a
comparison to the ice-skating data. Obtained from equations provided by Wilkie
(Wilkie, 1980 ), Saltin
(Saltin, 1973) and Davies
(Davies, 1981), the
three-colour curves are based on the assumption that the available fraction of
the metabolic power used for a physical activity is inversely related to the
time to exhaustion (from the left; black, 40 s–10 min; light grey, 10
min–1 h; dark grey, 1–24 h). For the calculations, the maximum
metabolic power available has been set at 21.3 W kg–1. The
light grey curves are iso-duration speed/distance pairs; the open squares
represent the actual records in ice-skating and the open circles show records
for cross-country skiing, reported as a means of comparison. Example: the
energy cost of skating on bones (1800 BC) is indicated by the thick 345 J
m–1 iso-cost line. The intersection between this iso-cost
line and the light 10 min iso-time line shows that in 10 min, for an energy
cost of 345 J m–1, a skater could cover a distance of 2638 m
at an average speed of 4.4 m s–1 before exhaustion. The
energy cost of modern ice-skating is only 99 J m–1, less than
one-third of the energy cost associated with skating on bones. Consequently,
in 10 min, a distance of almost 10 km can be travelled at an average speed of
 16 m s–1 before exhaustion, as indicated by the
intersection between the 99 J m–1 iso-cost curve and the 10
min iso-time line.
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