The purpose of this study was to compare peak aerobic capacity in female triathletes in 3 modes of exercise: treadmill, cycle, and arm ergometer. A second purpose was to determine the extent that physiologic criteria for achieving (V)over dotO(2)peak were reached in each mode of exercise. Six criteria were examined: (V)over dotO(2)plateau, heart rate (HR), blood lactate concentration (BLC), respiratory exchange ratio, oxygen saturation, and rating of perceived exertion (RPE). Twelve recreational level female triathletes completed maximal tests on the treadmill, stationary bike, and arm ergometer. Results indicated (V)over dotO(2)peak (ml.kg(-1).min(-1)) is highest on a treadmill (46.8 +/- 2.1), intermediate in cycling (40.7 +/- 5.0), and lowest in arm ergometry (28.2 +/- 3.3) with mean differences being significant (p <= 0.05). Blood lactate concentration and RPE criteria were met by the highest number of subjects across the 3 modes of testing while the HR criterion was not achieved in any participant in arm ergometry and only 2 in cycling. It was concluded that in moderately trained recreational level triathletes, (V)over dotO(2)peak is highest in running and lowest in arm ergometry. Criteria for achieving (V)over dotO(2)peak most frequently were blood lactate level and RPE. Coaches and researchers should appreciate that (V)over dotO(2)peak values of moderately trained triathletes differ considerably in contrast to elite triathletes and tend to be highest on the treadmill and lowest in arm ergometry. Also, criteria used to determine achievement of (V)over dotO(2)peak should be carefully selected and seem to be best achieved using BLC and RPE.