Exercise Target Heart Rate Prescription in Obese Individuals

Abstract

PURPOSE: The purpose of the present study was to assess the equivalency between the VO2 reserve (VO2R), heart rate reserve (HRR), and maximal heart rate (HRmax) methods to prescribe an exercise target heart rate (HR) following a maximal graded exercise test in obese individuals. METHODS: Sixty-eight overweight to severely obese and sedentary adults (mean ± standard deviation) (BMI=34.9±4.6 kg·m−2, resting HR=84±11 bpm, resting VO2=2.5±0.5 ml·kg−1, HRmax=178±11 bpm, VO2peak=25.1±4.3 ml·kg−1·min−1) performed a Bruce ramp protocol on a treadmill. Resting heart rate was determined after 15 min of rest in a sitting position prior the stress test and was used for HRR calculation. Resting metabolism was measured on a separate occasion in a recumbent position and was used for VO2R calculation. Exercise target HR was defined at 6 relative intensities (I-) where I-1=40%/64%, I-2=50%/71%, I-3=60%/77%, I-4=70%/84%, I-5=80%/91%, and I-6=85%/94% of VO2R or HRR / HRmax respectively, according to ACSM's guidelines. Six one way repeated measure ANOVAs were done to compare target HR between the 3 proposed methods for each intensity. Three one way repeated measure ANOVAs (6 intensities) were performed to compare delta target HR between HRR-VO2R, HRmax-VO2R, and HRmax-HRR. RESULTS: Target HR calculated by HRR was 6±7, 7±8, 7±8, 6±8, 5±7, and 4±6 bpm significantly higher (p<0.001) than VO2R from I-1 to I-6 respectively. Target HR calculated by HRmax was not significantly different than VO2R at I-1 (−2±9) and I-2 (1±10) but was significantly higher (p<0.01) from I-3 to I-6 and was equal to 3±9, 5±8, 8±7, and 7±7 bpm respectively. Target HR calculated by HRmax was−9±6,−6±5, and−4±4 bpm significantly lower (p<0.001) than HRR from I-1 to I-3, not significantly different at I-4 (−1±3), and significantly higher (p<0.001) at I-5 (2±2) and I-6 (3±2). No intensity effect for delta target HR between HRR and VO2R was found. Delta target HR between HRmax and VO2R were significantly different (p<0.001) from each other from I-1 to I-5 but not between I-5 and I-6. Delta target HR between HRmax and HRR were significantly different from each other between intensities (p<0.001). CONCLUSIONS: The slightly but significant (6±7 bpm) difference between target HR calculated by HRR and VO2R is constant among intensities. However, the difference between target HR calculated by HRmax and VO2R or HRmax and HRR both fluctuate between relative intensities. These results have their importance for exercise target HR prescription in obese individuals.