Short Trail Running Race: Beyond the Classic Model for Endurance Running Performance.

Purpose: To examine the extent to which the classical physiological variables of endurance running performance [VO2max, %VO2max at ventilatory threshold (VT), and running economy (RE)], but also muscle strength factors contribute to short trail running (TR) performance. Methods: A homogeneous group of nine highly-trained trail runners performed an official TR race (27-km) and laboratory-based sessions to determine VO2max, %VO2max at VT, level RE (RE0%) and RE on a +10% slope (RE+10%), voluntary concentric and eccentric knee extension torques (MVCCon and MVCEcc, respectively), local endurance assessed by a fatigue index (FI) and a time to exhaustion at 87.5% of the velocity associated with VO2max. A simple regression method and commonality analysis identifying unique and common coefficients of each independent variable were used to determine the best predictors for the TR race time (dependent variable). Results: Pearson correlations showed that FI and VO2max had the highest correlations (r = 0.91 and r = -0.76, respectively) with TR performance. The other selected variables were not significantly correlated with TR performance. The analysis of unique and common coefficients of relative VO2max, %VO2max at VT and RE0% provides a low prediction of TR performance (R2 = 0.48). However, adding FI and RE+10% (instead of RE0%) markedly improved the predictive power of the model (R2 = 0.98). FI and VO2max showed the highest unique (respectively 49.7 and 21.0% of total effect) and common (27.0% of total effect) contributions to the regression equation. Conclusions: The classic endurance running model does not allow meaningful prediction of short TR performance. Incorporating more specific factors to TR such as local endurance and gradient-specific RE testing procedures should be considered to better characterize short TR performance. (C) 2017 American College of Sports Medicine

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