Body mass scaling of projected frontal area in competitive cyclists

The primary purpose of this study was to evaluate the scaling relationship between body mass (m(b)) and projected frontal area (A(P)) of competitive m ale cyclists whilst allowing statistically for the influence of bicycle geo metry. A group of 21 cyclists [mean m(b) 74.4 (SD 7.2) kg, mean height 1.82 (SD 0.06) in, mean age 23.6 (SD 5.1) years] volunteered to have A(p) deter mined from photographs at three trunk angles (TA: 5 degrees, 15 degrees, 25 degrees) for each of three seat-tube angles (STA: 70 degrees, 75 degrees, 80 degrees) using a modified cycle ergometer. Using multiple log-linear reg ression analysis procedures, the following equation was developed: Body A(p ) (meters squared) = 0.00433x(STA(0.172))x(TA(0.0965))x(m(b)(0.762))(r(2) = 0.73, SEE = 0.017 m(2)) (n = 183 images total). This equation indicates th at after allowing for the independent influence of STA and TA on AP, AP was proportional to m(b) raised to the + 0.762 power (i.e. A(p)proportional to m(b)(0.762)). The 95% confidence interval for this exponent (0.670-0.854) b arely included the theoretical two-thirds value but not the + 0.55 value fo r A(p) or the +0.32 value for submaximal metabolic power ((W)) over dot(s)) of outdoor cycling reported in the literature. Further analysis of wind tu nnel data reported in the literature suggests that the coefficient of drag (CD) is proportional to m(b) raised to the -0.45 power. When combined with the present study findings, it is suggested that the drag area (C(D)xA(p)), which should be proportional to (W) over dot(s) at submaximal cycling velo cities, is proportional to m(b) to the + 0.312 power (i.e. C(D)xA(P)proport ional tom(b)(-0.45))x(m(b) (+0.762)) = m(b) (+0.312)), which is consistent with the +0.32 exponent for (W) over dot(s) in the literature.