Body mass scaling of frontal area in competitive cyclists not using aero-handlebars

This study was designed to evaluate the scaling relationship between body mass ( m(b)) and projected frontal area ( A(P)) in competitive male cyclists using traditional drop-style handlebars. A group of 21 male cyclists [mean (SD) m(b) 74.4 (7.2) kg, height 1.82 (0.06) m, age 23.6 (5.1) years] had A(P) determined from photographs taken while seated on their own racing bicycles in four body positions: (1) stem position; (2) brake hoods position; (3) drops position; (4) traditional aero-position. For each position, A(P) for the body of the cyclist (Body A(P)), as well as the cyclist and his bicycle (Total A(P)), were determined. Body A(P) was significantly smaller than Total A(P) in all four positions by a nearly constant bicycle A(P) of 0.117-0.124 m(2). Using multiple log-linear regression analysis procedures, prediction equations were developed for both Body A(P) and Total A(P) (dependent variables) using a cluster of binary-coded variables to indicate body position and m(b) as independent variables ( n=88 observations). The regression analysis revealed that Body A(P) scaled with m(b) to the +0.720 power [95% confidence interval (CI): 0.585-0.855], which did not differ significantly from the +0.762 exponent reported previously for Body A(P) whilst using aero-handlebars. In contrast, Total A(P) scaled with m(b) to the +0.594 power (95% CI: 0.468-0.720) which was significantly lower than +0.762 exponent reported previously. The lower exponent for Total A(P) is explained by the nearly constant contribution of the bicycle A(P) to Total A(P) (mean bicycle A(P)=0.122 m(2)). These data help to explain the determinants of A(P) and aerodynamic drag in competitive male cyclists who use the traditional body postures.