INTRODUCTION: External power output in an endurance sport such as cross-country skiing can, from a physiological perspective, be explained as the sum of aerobic and anaerobic metabolic rates multiplied by the gross efficiency (GE). As cross-country skiing performance is highly dependent on all three performance factors, a model that could predict performance changes due to alterations in the respective factors would be beneficial for evaluating the training response and/or ability of an athlete. Therefore, this study was designed to develop and calibrate a performance model for time-trial (TT) roller-skiing on an indoor treadmill using the skating gear 3 subtechnique. METHODS: Eleven highly-trained female and twelve highly-trained male cross-country skiers (VO2_peak of 57 ± 3 and 69 ± 5 mL kg[BM] -1 min -1, respectively) were recruited for this study. Following a 992-m TT (4° uphill) familiarization trial, participants performed a submaximal protocol for the determination of GE and three successive 992-m TTs (each TT separated by 25 min active and passive rest). The average TT performance was used to determine the peak aerobic metabolic rate (MR_ae,peak) and peak anaerobic energy supply (E_an,peak). The model was based on the power balance of mean power supply and mean power demand based on power due to gravity and rolling resistance. The mean power supply (P_s) was modeled by MR_ae,peak, E_an,peak, and GE. The fractional utilization of MR_ae,peak was modeled as a function of TT duration. RESULTS: The model-to-measurement mean difference in TT time was -2.8 s (P = 0.034) and -0.3 s (P = 0.726) for females and males, respectively. The typical error (TE), expressed as a percentage, was 1.1% for both sex groups. A sensitivity analysis revealed that a 5.0% increase in the GE ratio resulted in a 5.3% higher TT velocity, a 5.0% increase of the MR_ae,peak resulted in a 4.0% higher TT velocity, whereas a 22% increase in E_an,peak resulted in a 5.9% higher TT velocity. Based on average group values for the three performance factors (i.e., MR_ae,peak, E_an,peak, and GE), longer TT performances were predicted. DISCUSSION/CONCLUSION: The study findings are relevant for the interpretation of changes in physiological performance factors and how these relate to performance over various TT distances. Such information would be of considerable value to coaches and athletes.
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