Zuliani and colleagues carried out a study to investigate the
metabolic effect of cross-country skiing. Subjects were participants
in a 24 hour cross-country relay. Age, weight (kg), and blood CPK
concentrations after 12 hours of the race were recorded.

Data source: Zuliani, U., Mandras, A., Beltrami, G.F., Bonetti,
A., Montani, G., and Novarini, A. (1983). ``Metabolic modifications
caused by sport activity: effect in leisure-time cross-country
skiers,'' Journal of Sports Medicine and Physical Fitness,
23:385-392.