Allometric scaling of uphill cycling performance

Previous laboratory-based investigations have identified optimal body mass scaling exponents in the range 0.79-0.91 for uphill cycling. The purpose of this investigation was to evaluate whether or not these exponents are also valid in a field setting. A proportional allometric model was used to predict the optimal power-to-mass ratios associated with road-based uphill time-trial cycling performance. The optimal power function models predicting mean cycle speed during a 5.3 km, 5.4% road hill-climb time-trial were (V̇O _2max·m^-1.24)^0.55 and (RMP _max·m^-1.04)^0.54, explained variance being 84.6% and 70.5%, respectively. Slightly higher mass exponents were observed when the mass predictor was replaced with the combined mass of cyclist and equipment (m_C). Uphill cycling speed was proportional to (V̇O_2max·m_C ^-1.33)^0.57 and (RMP_max·m_C ^-1.10)^0.59. The curvilinear exponents, 0.54-0.59, identified a relatively strong curvilinear relationship between cycling speed and energy cost, suggesting that air resistance remains influential when cycling up a gradient of 5.4%. These results provide some support for previously reported uphill cycling mass exponents derived in laboratories. However, the exponents reported here were a little higher than those reported previously, a finding possibly explained by a lack of geometric similarity in this sample.