The purpose of this study was to determine to what extent anthropometric characteristics account for cycling peak power during growth. Five hundred and six male subjects aged 7.5-18 years performed three brief maximal sprints on a friction-loaded cycle ergometer. Cycling peak power (CPP) was calculated including the flywheel inertia of the device. Fat-free mass (FFM) and lean leg volume (LLV) were assessed by anthropometry. Anthropometric characteristics increased significantly during growth (p<0.001) but plateaued from about 16 years of age (p > 0.3). The same pattern was observed for CPP, while the time to reach CPP decreased during growth. CPP correlated as highly with LLV as with FFM and both parameters may therefore be interchanged. However, in non weight-bearing exercises, such as cycling, it seems more relevant to "normalise" leg power for LLV. Multiple stepwise regression, using an allometric model, showed that a large part of the variance of CPP was explained by LLV (88.2%, p<0.001). However, age and time to reach peak power also contributed significantly (approximately 3 %, p < 0.001). The prediction of CPP revealed that FFM and age contributed to 92.2% of the total variance of CPP. Because of its practicability, fat-free mass is particularly useful in prospective studies. Although the effects of dimensional changes in CPP during growth are obvious, undetermined qualitative changes of muscle function during maturation must be considered.