The spectacular improvements of the 1-h world record in cycling in the last four years have highlighted the importance of aerodynamics in modern bicycle racing. We have investigated the metabolic consequences of the low-crouched aero-positions necessary to reduce air drag. In this study, 14 elite male bicycle racers (24.0 +/- 1.0 yr, VO2max 69.4 +/- 0.5 mL.kg-1.min-1) were tested for oxygen consumption (VO2) and heart rate (HR) at 70% (302.6 +/- 5.3 W) of their individual VO2max in three different riding positions during a single test run. The subjects rode their racing bicycles on a wind braked roller; the sequence of the three following positions was randomized: 1) upright cycling (UP), cadence 90 rpm; 2) hands on drops (DP), 90 rpm; and 3) hands on clip-on aero-handlebars (AP), 90 rpm. VO2 and HR values in AP were significantly higher by 1.5 mL.kg-1.min-1 and 5 beats.min-1, respectively, compared with UP. We concluded that riding a bicycle in an extreme aero-position increases the metabolic cost of cycling when wind resistance is not taken into account. However, when the mechanical power losses of 9 W (estimated by the VO2 increase) are compared with the expected aerodynamic power savings of approximately 100 W, it appears that aerodynamic advantages by far outweight their metabolic cost.