The influence of race duration on oxygen demand, uptake and deficit in competitive cross-country skiers

To measure oxygen demand, uptake, and deficits in competitive cross-country skiers during outdoor roller skiing at different competition durations, ranging from the endurance domain to the sprint domain.

Ten competitive cross-country skiers (6 males; \(\dot{\text{V}}\) $\dot{\text{V}}$ O_2max 78 ± 3 and 4 females; \(\dot{\text{V}}\) $\dot{\text{V}}$ O_2max 62 ± 3 mL∙kg⁻¹∙min⁻¹) raced time trials consisting of 1, 2, and 4 laps in a 1.6 km racecourse in a randomized order with 35 min recovery in-between. Oxygen uptake was measured using a wearable metabolic system while oxygen demand was estimated from kinematic data (GPS and IMU) and an athlete-specific model of skiing economy. Skiing economy and \(\dot{\text{V}}\) $\dot{\text{V}}$ O_2max was established on a separate test day using six submaximal constant-load trials at different speeds and inclines, and one maximal-effort trial on a roller-skiing treadmill.

Average oxygen demand was 112 ± 8%, 103 ± 7% and 98 ± 7% of \(\dot{\text{V}}\) $\dot{\text{V}}$ O_2max during the 1 (3:37 ± 0:20 m:ss), 2 (7:36 ± 0:38 m:ss) and 4 (15:43 ± 1:26 m:ss) lap time trials, respectively, and appeared to follow an inverse relationship with time-trial duration. Average oxygen uptake was unaffected by race length (86 ± 5%, 86 ± 5%, and 86 ± 7% of \(\dot{\text{V}}\) $\dot{\text{V}}$ O_2max, respectively). Accumulated oxygen deficit at the end of each time trial was 85 ± 13, 106 ± 32 and 158 ± 62 mL∙kg⁻¹, while oxygen deficits per work bout was 23 ± 3, 18 ± 3 and 16 ± 3 mL∙kg⁻¹ for the 1, 2, and 4-lap time trials, respectively.

Elite cross-country skiers adjust their pacing strategies from attaining relatively small oxygen deficits per work bout in the endurance domain, to larger deficits in the sprint domain. This indicates a shift in strategy from prioritizing stable work-economy and rate-of-recovery in the endurance domain, to maximizing power output in the sprint domain.