BODY MASS SCALING OF FRONTAL AREA IN CYCLISTS 1124

Abstract

Swain (1994) found that projected frontal area (AP, m2) for cyclists in a “racing position” scaled with body mass (MB) to the 0.55 power (ie AP α MB0.55), which is lower than the 0.67 exponent predicted theoretically (˙Astrand and Rodahl, 1986). To evaluate this contradiction, the present study sought to determine how AP scaled with MB after statistically controlling for anthropometric and bicycle geometry covariates in 21 male cyclists(Mean±SD: 23.6±5.1 yrs, 74.4±7.2 kg, 10.8±3.5% fat). AP for each subject was measured at 3 trunk angles (TAs: 5°, 15°, 30°) at each of 3 seat-tube angles (STAs: 70°, 75°, 80°) while seated stationary on a Monark cycle ergometer modified with adjustable seat and handlebar positioning and aerobars. Images from 35 mm film slides of each subject were hand digitized to compute AP using standard planometry procedures (n = 189 slides). Multiple log-linear regression analyses (α = 0.05) were used to determined the MB exponent for AP while using TA, STA, body height (1.82±0.06 m), and biacromial diameter (0.48±0.02 m) as covariates. The resulting regression model (R2=0.84; P<0.001) found that AP scaled with MB to the 0.41 power (95% CI:0.30-0.52). Thus, AP scaled to a lower power than predicted by the literature (0.41 vs 0.55 or 0.67). Clearly, the statistical control of anthropometric and bicycle geometry covariates was very important to determining the MB exponent for AP.