Physiological demands of elite cross-country skiing during a real competition.

The aim of this study was to assess different physiological variables before and after a 5 km (women) and 10 km (men) cross-country skiing competition to determine potential mechanisms of fatigue. Fourteen elite-level skiers competed in an official cross-country skiing competition using the classical style (9 men and 5 women). Instantaneous skiing velocity was measured during the race by means of 15-Hz GPS devices. Before and after the race, a sample of venous blood was obtained to assess changes in blood lactate and serum electrolyte and myoglobin concentrations. Pre-to-post-race changes in blood oxygen saturation, forced vital capacity during a spirometry test, jump height during a countermovement jump, and handgrip force were also measured. Mean race speed was 15.8±2.5 and 15.4±1.5 km·h while mean heart rate was 171±6 and 177±3 beat·min for men and women, respectively. There were no significant pre-to-post-race changes in jump height, handgrip force and forced vital capacity in men and women. Blood oxygen saturation was reduced from pre-to-post-race in men (95.9±2.1 to 93.1±2.3%, p=0.02) and women (97.8±1.1 to 92.4±2.1%, p<0.01) while blood lactate concentration increased at the end of the race in men (1.4±0.5 to 4.9±2.1 mmol·L, p<0.01) and women (1.9±0.1 to 6.9±3.2 mmol·L, p<0.01). After the race, blood markers of muscle damage were at low concentrations while serum electrolytes remained unchanged. Fatigue in 5 km and 10 km cross-country skiing competitions was related to a reduced blood oxygen carrying capacity and presumably increased muscle and blood acidosis while the influence of exercise-induced muscle damage on fatigue was minor.