The American College of Sports Medicine advocates the use of a percentage of maximal oxygen uptake reserve (%VO2R) for exercise prescription purposes because it's thought to provide a close match with percentage of heart rate reserve (%HRR) than a given percentage of maximal oxygen uptake (%VO2max). However, some recent studies have challenged the validity of this matching. The purpose of this study was to assess the association of body mass index (BMI) with the matching of %HRR and %VO2R during graded exercise testing. The study sample included 626 subjects (281 men; 345 women); mean age of 45.5+11.7 years; mean BMI of 27.9+5.4 kg .m-2) who completed a maximal treadmill test to volitional fatigue using the BSU/Bruce Ramp protocol. The distribution of BMI measures within the sample was 31.4% <25; 38% between 25.0 and 29.9; 17.9% between 30 and 34.9%; 8.8% between 35 and 39.9%; and 3.1% were > 40 kg•m"2. Subjects were excluded from the analysis if they failed to achieve a peak RER > LO during the maximal exercise test, possessed pulmonary or cardiovascular disease (excluding hypertension), or incomplete/erroneous submaximal heart rate and/or V02 data that was unable to be retrieved from subject's existing file. Heart rate and VO2 data from minutes 3, 6, and 9 were converted into %HRR and %VO2R, with 3.5 ml•kg-'•min' serving to represent resting VO2. The relative exercise intensity for minutes 3, 6, and 9 represented 39.7 +12.2, 62.9 ± 15.6, and 80.8 ± 12.5% of VO2R, respectively and 43.1 f 12.6, 64.7 ± 14.9, and 83.5 + 10.6% of HRR. %HRR significantly overestimated %VO2R at each measurement point during the exercise test with mean differences 3.3, 2.0, and 3.8%, respectively (p<0.05). The association of BMI with the matching of %HRR and %VO2R was assessed by correlation with the difference the scores (AHRRVO2R) at each specified time during exercise test. Correlations for BMI and AHRRVO2R were -0.102, -0.175, and -0.231 for minutes 3,6, and 9, respectively (p<0.05). These results demonstrate a low association between BMI and the matching of HRR and VO2R.