Influence of body size on oxygen consumption during bicycling

Energy in bicycling is primarily expended to overcome air resistance, which is proportional to a cyclist's surface area (SA). Thus we hypothesized that large cyclists should have a lower O₂ consumption normalized to body weight (V̇O₂/BW) than small cyclists because of the former's lower SA/BW. We measured the V̇O₂/BW of small (BW = 59.4 ± 4.1 kg) and large (BW = 84.4 ± 3.2 kg) cyclists while they bicycled on a flat road at 10, 15, and 20 mph. The large cyclists had a 22% lower V̇O₂/BW than the small cyclists at all speeds. However, the SA/BW ratio of the large cyclists was only 11% lower than that of the small cyclists. We then photographically determined the frontal area (FA) of the cyclists in a racing posture, and found that the large cyclists had a 16% lower FA/BW ratio than the small cyclists. We conclude that 1) large cyclists are at a distinct advantage, in terms of V̇O₂/BW, while bicycling on level roads, and 2) this advantage is principally due to their lower FA/BW ratio.