Critical Power And Aerodynamic Drag Accurately Predict Road Time-trial Performance In British Champion Cyclists

Abstract

PURPOSE: This case study examined the efficacy of wind-tunnel derived measures of aerodynamic drag combined with the critical power model to predict road cycling time trial performance. METHODS: One male (73.1 kg) and one female (68.0 kg) cyclist each won individual time trial races against the clock over 10, 25, 50 and 100 miles (16.1, 40.2, 80.5, 160.9 km; British Championships; out-and-back road courses). Power was recorded with a SRM Powermeter (SRM, Germany). Separately, critical power (CP) and anaerobic work capacity (AWC) were determined from the power-time relationship of race efforts of 20 to 50 min. Aerodynamic drag force was determined in a wind-tunnel at 13.9 m/s at 0° yaw (Mercedes GP F1). Course elevation profile was obtained via GPS records and cycling speed was predicted both a priori and in retrospect from estimated or known power-time data using the equations of Martin et al., (2006). RESULTS: CP was 416 and 299 W; AWC was 25.6 and 15.6 kJ (male and female respectively). Over the shortest duration race, predicted and actual race powers closely agreed, but not in longer races. When the actual race power was used in retrospect to predict speed, the difference between the actual and predicted times was on average 0.2%, and no greater than 1.1%, with no apparent bias. CONCLUSIONS: The predictive strength of the power-speed relationship (previously established for track cycling) holds true on the open road and allows a remarkably close estimate of race time. Small differences between the predicted and actual times are most likely derived from the effect of the prevailing wind and unaccounted-for differences in rolling resistance as well as the variable distribution of power across the course. These latter points will be elaborated upon.Table