The aerobic capacity (AC) model for the evolution of vertebrate endothermy posits that selection for high sustained activity levels required increased maximal oxygen consumption (VO2max), and that increased basal metabolic rate (BMR) evolved as a correlated response, such that VO2max/BMR remained relatively constant. A correlated response in BMR is based on presumed causal, mechanistic links (e.g. shared biochemical or physiological pathways) with VO2max that have yet to be identified. The AC model has also been considered more generally with respect to vertebrate energetics. The literature offers mixed support for the AC model. We tested the hypothesis that selection for daily activity levels in mice, which is known to have increased VO2max (and endurance capacity) during forced treadmill exercise, has also elevated BMR. We measured VO2max, BMR, and organ masses of 50 females from generation 88 of an ongoing experiment in which 4 replicate lines of High Runner (HR) mice are bred for daily running distance and compared with 4 non-selected Control (C) lines. With body mass as a covariate, HR mice had a significantly elevated VO2max (+14%), as reported in several previous studies, and also a significantly elevated BMR (+8%). These results are partially consistent with the AC model, as the increase in BMR was somewhat less than for VO2max. Although higher VO2max is often associated with larger hearts, lungs, muscles, and increased hematocrit, HR mice from this sample were not statistically higher for any of these traits. As well, BMR should be positively associated with the relative size of heart, brain, liver, kidney, and spleen, but again HR mice did not differ from C for any of these organ masses (with body mass as a covariate).