Aerodynamic drag in field cycling with special reference to the Obree's position

In cycling at race speeds, 90% of total resistance opposing motion, R T(N) T depends on aerodynamic drag of air, which is directly proportional to the effective frontal area, AC d(m2). R T was measured on a cyclist, in an open velodrome, in order to evaluate AC d in four different positions on a traditional bicycle: upright d position (UP), dropped position (DP), aero position (AP) and Obree's position (OP : the hands in support under the chest, the forearms tucked on the arms, the trunk tilted forward). R T was determined at different constant speeds, Vc(m s−1) with a special device (Max One), which allows the measurement of the external mechanical power P ext(W) in real conditions of cycling locomotion ext (R T = P ext Vc−1). Experiments were carried out in order to test the validity and the reproducibility of P ext provided by the measurement device. P ext was measured twice in the same experimental conditions (exercise on a treadmill against slopes varying from 1 to 14%) and no significant difference ...