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The reproducibility of the Bruce exercise test protocol for the determination of maximal aerobic capacity was evaluated in sedentary older women. Seventeen women between the ages of 51 and 68 yr performed five maximal graded exercise tests to volitional fatigue on a treadmill. ˙VO2max(mL·kg-1·min-1) values averaged 27.5 ± 1.1; 28.3 ± 1.3; 28.4 ± 1.3; 29.6 ± 1.5; and 28.2 ± 1.4 for trials 1-5, respectively, and were not significantly different. Criteria for a plateau in ˙VO2 at the point of exhaustion were met in 21 out of 85 tests (25%). The mean coefficient of variation in ˙VO2max for the subjects for the 5 tests was 6.5% (range, 2.0-14%). Pearson's correlation coefficients for the study variables were significant, indicating good agreement between repeated tests (r2: between 0.70 to 0.89). Although there were no significant differences among the mean ˙VO2max values in the 5 trials, 11 subjects had a 1.0 mL·kg-1·min-1 or greater increase in the˙VO2max from test 1 to test 2, and only 6 subjects had no change or a decrease in ˙VO2max. The mean difference between T2 and T3 was lower (T1 vs T2: 0.8 mL·kg-1·min-1, T2 vs T3: 0.1 mL·kg-1·min-1) indicating slightly better agreement between the second and third test. Estimates of the between and within subject variance revealed a low within subject variance (4.2(mL·kg-1·min-1)2) compared to the between subject variance (22.1(mL·kg-1·min-1)2). This study demonstrates that a commonly used exercise testing protocol generates highly reproducible measurements of ˙VO2max in women between 51 and 68 yr. The mean differences between tests and the high level of agreement between repeated tests suggests that a single measurement of˙VO2max can be performed to assess functional aerobic capacity in this population.