PWC 75%/kg, a fitness index not linked to resting heart rate: testing procedure and reference values.

Abstract

To develop a fitness index unlinked to resting heart rate and suitable for clinical use, and to obtain reference values of this new index for healthy subjects. Cross-sectional study. Research laboratory. A volunteer sample of healthy subjects (N=100; 50 men; age range, 20-70y) randomly recruited from the general community. Not applicable. Participants performed a submaximal, multistage cycle ergometer test. A new fitness index, the physical working capacity at 75% of the predicted maximal heart rate per kilogram of body weight (PWC(75%)/kg), was calculated. Its concordance with a previously described fitness index and its relationship with age were examined, as well as differences attributable to sex and lifestyle. Reference values of the PWC(75%)/kg (mean ± SD and 95% confidence interval) were calculated and categorized by age classes of 10 years and by sex. The intraclass correlation coefficient (ICC) between PWC(75%)/kg and the working capacity index at 65% of the heart rate reserve per kilogram of body weight (WCI(65%HRreserve)/kg) was very high (ICC=.96, P<.001), indicating that the fitness index can be estimated without measuring the resting heart rate. PWC(75%)/kg decreased as age increased. The average PWC(75%)/kg was significantly higher in men than in women (P<.001), and in active than in inactive subjects (P<.01). This study presents a new fitness index, the PWC(75%)/kg, which is suitable for measuring fitness in active and sedentary people aged 20 to 70 years. It may also be a suitable fitness index for selected chronically ill individuals. This study also provides reference values of the PWC(75%)/kg obtained from healthy men and women.