Treadmill grade as a determinant of roller skiing oxygen consumption at a constant external power demand
Reinking, Bryant William
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Cross-country (XC) skiing is typically considered an aerobic activity, yet the accumulated oxygen deficit (SigmaO ₂-deficit), a representation of anaerobic capacity, has shown to be a valuable predictor of XC skiing performance. The SigmaO ₂-deficit is calculated as the difference between the predicted oxygen consumption (VO ₂) demand and the measured VO ₂ cost during a roller skiing time-trial protocol (RSTT). To determine VO ₂ demand, a lactate threshold (LT) protocol is performed with the purpose of plotting external power demand (TEPD) against measured steady-state VO ₂ cost. A regression line is fit and used to predict the VO ₂ demand of the RSTT. A possible limitation of this methodology is that it is common to use a lower treadmill grade for the LT protocol than that used for the RSTT. In order to validate the use of the LT protocol as a component of calculating the SigmaO ₂-deficit, this study investigated the influence of different treadmill grades on the linear relationship between VO ₂ cost and TEPD in collegiate XC skiers. Fifteen female collegiate XC skiers (Mean + or - SD, Range: 20 + or - 1, 18-24 years) completed three laboratory visits within a 10 day period. During each visit, skiers completed a single LT protocol at one of three treadmill grades (2°, 3°, 4°), for the purpose of measuring VO ₂ while roller skiing. The TEPD values of each treadmill stage were computed as the sum of both rolling and gravitational resistances. Steady-state VO ₂ values were plotted against corresponding TEPD values and a regression line was fit to the data. The resulting slope and intercept terms for each line were compared across treadmill grades using two-way repeated measures ANOVA and Scheffe's post hoc test (alpha=0.05). Neither the slopes (P=0.31) nor the intercepts (P=0.63) were significantly different between treadmill grades. This study demonstrated that the slope and the intercept terms of the VO ₂ cost - TEPD regression line were not significantly influenced by treadmill grades between 2-4°, in female collegiate XC skiers. Consequently, this study indicates that the treadmill grade of LT roller skiing protocols will not significantly affect a skier's calculated SigmaO ₂-deficit.