Comparing methods for prescribing exercise for individuals with chronic heart failure

This study examined the accuracy of current recommended guidelines for prescribing exercise intensity using the methods of percentage of heart rate reserve (%HRR), percentage of VO₂ peak (%VO₂peak) and percentage of VO₂ reserve (%VO₂R) in a clinical population of chronic heart failure (CHF) patients. The precision of prescription of exercise intensity for 45 patients with stable CHF (39:6 M:F, 65±9 yrs (mean±SD)) was investigated. VO₂peak testing is relatively common among patients with cardiac disease, but the assessment of VO₂rest is not common practice and the accepted standard value of 3.5 mL/kg/min is assumed in the application of %VO2R (%VO₂R_3.5). In this study, VO₂rest was recorded for 3 min prior to the start of a symptom-limited exercise test on a cycle ergometer. Target exercise intensities were calculated using the VO₂ corresponding to 50 or 80 %HRR, VO₂peak and VO₂R. The VO₂ values were then converted into prescribed speeds on a treadmill in km/hr at 1 %grade using ACSM’s metabolic equation for walking. Target intensities and prescribed treadmill speeds were also calculated with the %VO₂R method using the mean VO₂rest value of participants (3.9 mL/kg/min) (%VO₂R_3.9). This was then compared to the exercise intensities and prescribed treadmill speeds using patient’s measured VO₂rest. Error in prescription correlates the difference between %VO₂R_3.5 and %VO₂R_3.9 compared to %VO₂R with measured VO₂rest. Prescription of exercise intensity through the %HRR method is imprecise for patients on medications that blunt the HR response to exercise. %VO₂R method offers a significant improvement in exercise prescription compared to %VO₂peak. However, a disparity of 10 % still exists in the %VO₂R method using the standard 3.5 mL/kg/min for VO₂rest in the %VO₂R equation. The mean measured VO₂rest in the 45 CHF patients was 11 % higher (3.9±0.8 mL/kg/min) than the standard value provided by ACSM. Applying the mean measured VO₂rest value of 3.9 mL/kg/min rather than the standard assumed value of 3.5 mL/kg/min proved to be closer to the prescribed intensity determined by the actual measured resting VO₂. These results suggest that the %HRR method should not be used to prescribe exercise intensity for CHF patients. Instead, VO₂ should be used to prescribe exercise intensity and be expressed as %VO₂R with measured variables (VO₂rest and VO₂peak).