The dependence of metabolic rate (MR) on body mass (M) is described by the general allometric equation MR=aM(b), where, a is a proportionality coefficient and b is the mass exponent. Darveau et al. [Nature 417 (2002), 166] proposed a novel 'multiple-causes' allometric cascade model as a unifying principle of the scaling of MR, at rest and during maximal exercise. We tested the validity of body mass exponents predicted from the model for submaximal and maximal aerobic exercise conditions in 1629 men. MRs were estimated from whole-body oxygen consumption during an incremental treadmill test to voluntary exhaustion. For both submaximal (b=0.83) and maximal (b=0.94) exercise requiring average oxygen consumption rates of around 5-11 times resting values, respectively, the obtained mass exponents were remarkably consistent with predicted values. Moreover, for maximal MR the global mass exponent was significantly greater than for submaximal aerobic metabolism, congruent with the allometric cascade model.