Purpose: For patients starting a cardiac rehabilitation program, exercise intensity often is set 20 beats per minute above the standing resting heart rate (RHR+20) or in a range of 11 to 13 on Borg's Scale for Rating of Perceived Exertion (RPE 11-13). The purpose of this study was to determine the actual exercise intensity, expressed as a percentage of peak oxygen uptake reserve (%VO2R) using these techniques.
Methods: For this study, 11 new referrals to a phase 2 cardiac rehabilitation program voluntarily underwent a symptom-limited exercise test and a field test that consisted of self-paced over-the-ground walking for 10 minutes at levels corresponding to RPE 11-13 and RHR+20. During both tests, gas exchange data were obtained via the Cosmed K4b and heart rate via the Polar monitor.
Results: The mean %VO2R at RHR+20 (41.8 +/- 12.3%) and RPE 11-13 (71 +/- 15.3% mL.kg.min) were significantly different. Exercise at RHR+20 resulted in 4 of the 11 patients (36%) exercising at less than 40% VO2R, 6 of the patients (55%) exercising at 40% to 60% VO2R, and 1 of the patients (9%) exercising at more than 60% VO2R. Exercise at RPE 11-13 resulted in 1 of the 11 patients (9%) exercising at less than 40% VO2R, 1 of the patients at exercising at 40% to 60% VO2R (9%), and 9 of the patients (82%) exercising at more than 60% VO2R.
Conclusions: The results of this study indicate that using RHR+20 or RPE 11-13 to prescribe exercise intensity during over-the-ground walking for phase 2 cardiac rehabilitation patients results in substantial intersubject variability and raises questions about the safety and efficacy of these approaches.