Clear criteria for maximal oxygen consumption (VO[subscript 2]max) determination in youth are not available, and no studies have examined this issue in girls. Our purpose was to determine whether different peak heart rate (HRpeak) and peak respiratory exchange ratio (RERpeak) cut points affect girls' (N = 453; M age = 13.3 years, SD = 0.1) VO[subscript 2]max during a maximal treadmill test. A multivariate analysis of variance revealed VO[subscript 2]max (ml[middle dot]kg[superscript -1]{middle dot]min[superscript -1]) differed significantly among HRpeak, 180-189 b[middle dot]min[superscript -1] = 34 (SD = 0.8), 190-194 b[middle dot]min[superscript -1] = 35 (SD = 0.9), 195-199 b[middle dot]min[superscript -1] = 38 (SD = 0.8), 200-204 b[middle dot]min[superscript -1] = 40 ml[middle dot]kg[superscript -1][middle dot]min[superscript]-1 (SD = 0.8), and [greater than or equal to 205 b[middle dot]min[superscript -1] = 42 ml[middle dot]kg[superscript -1][middle dot]min[superscript -1] (SD = 0.7) but not RERpeak. In studies where evidence of a VO[subscript 2] plateau was examined, peak oxygen consumption (VO[subscript 2]peak) did not differ between plateau and no-plateau groups. Although our results suggest the association between lower VO[subscript 2]peak and lower peak heart rate is a true cardiovascular limit to aerobic energy production, we cannot rule out participant effort. (Contains 5 tables.)