Rationale:
Exercise capacity is assessed at entry into phase II cardiac rehabilitation (CR) to assess the safety of exercise and to establish an exercise program. The results are also used by some private payers to determine the extent of coverage. Maximal exercise capacity can be derived from directly measured maximal oxygen uptake or estimated from tables quantified in metabolic equivalents (MET).
Objective:
The purpose of this study is to compare the accuracy of directly measured peak VO2 versus estimated MET values.
Methodology:
Between 1996 and 2004, peak VO2 was measured in 2896 patients entering into CR in Burlington, VT (1502) and Detroit, MI (1394). Peak VO2, expressed in mL*kg-1*min-1, was measured at peak exercise and converted to measured METs by dividing by 3.5. Estimated MET was calculated from peak exercise workload in miles per hour and percent elevation using the established conversion from the ACSM.
Results:
Mean peak VO2 for the entire cohort was 17.9 +/- 6.0 mL* kg-1 * min-1 or 5.1 METs. Estimated peak MET was 6.5 +/- 2.8 overestimating measured peak METs by 25%. Peak VO2 was 14.4 +/- 3.9 (4.1 MET) and 19.3 +/- 6.1 (5.5 MET) mL* kg-1 * min-1 in women and men, respectively. The mean overestimation was 1.2 +/- 0.4 (+23%) and 1.3 +/- 0.6 (+30%) in women and men, respectively. The correlation coefficient between estimated peak METs and measured peak METs (calculated from measured peak VO2) was R = 0.48 overall (P < 0.0001). This correlation was higher in women (R = 0.66) than in men (R = 0.39), both P < 0.001.
Conclusions:
These results demonstrate that utilizing the MET values from existing tables systematically overestimates measured METs and implies a higher level of fitness than exists. This has important implications for patients entering CR because overestimating functional capacity may reduce the number of sessions afforded the patient through their insurance policy.