Oxygen Demand, Uptake, and Deficits in Elite Cross-country Skiers during a 15-km Race

Purpose: To quantify the repeated oxygen deficits attained during intermittent endurance exercise by measuring oxygen consumption (V[Combining Dot Above]O2) and oxygen demand (V[Combining Dot Above]O2dem) throughout a simulated roller ski race. Methods: Eight male elite cross-country skiers (V[Combining Dot Above]O2,peak 77.4 ± 4.4 mL·min-1·kg-1) raced a 13.5 km roller ski time-trial on a World Cup course. On two additional days, athletes completed (i) 6 sub-maximal loads (à 5 min) and a ~ 4 min maximal trial to establish athlete-specific estimates of skiing economy, V[Combining Dot Above]O2,peak, and maximal ΣO2def (MAOD); and (ii) a simulation of the time-trial on a roller skiing treadmill. During the simulation, external work rate (Pprop) and skiing speed (v) were adjusted to match the Pprop and v measured during the time-trial, and pulmonary V[Combining Dot Above]O2 was measured breath-by-breath. V[Combining Dot Above]O2dem and ΣO2def were calculated using an athlete-specific model for skiing economy throughout the treadmill simulation. Results: During the treadmill simulation V[Combining Dot Above]O2 was on average 0.77V[Combining Dot Above]O2,peak, and active V[Combining Dot Above]O2dem, (i.e., excluding the time in simulated downhills), was on average 1.01V[Combining Dot Above]O2,peak. The athletes repeatedly attained substantial oxygen deficits in individual uphill sections of the treadmill simulation, but the deficits were typically small compared to their MAOD (average 14%, range ~0-50%). However, the ΣO2def summed over all periods of active propulsion was on average 3.8MAOD. Conclusion: Athletes repeatedly attain substantial oxygen deficits in the uphill segments of a distance cross-country ski race. Furthermore, the total accumulated oxygen deficit of all these segments is several times higher than the athletes’ MAODs. This suggests that rapid recovery of the energy stores represented by the oxygen deficit is necessary during downhill sections, and that this might be an important determinant of distance skiing performance.