PWC75%/kg, a Fitness Index Not Linked to Resting Heart Rate: Testing Procedure and Reference Values

Batcho CS, Thonnard J-L, Nielens H. PWC75%/kg, a fitness index not linked to resting heart rate: testing procedure and reference values.ObjectivesTo 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.DesignCross-sectional study.SettingResearch laboratory.ParticipantsA volunteer sample of healthy subjects (N=100; 50 men; age range, 20–70y) randomly recruited from the general community.InterventionsNot applicable.Main Outcome MeasuresParticipants 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 (PWC75%/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 PWC75%/kg (mean ± SD and 95% confidence interval) were calculated and categorized by age classes of 10 years and by sex.ResultsThe intraclass correlation coefficient (ICC) between PWC75%/kg and the working capacity index at 65% of the heart rate reserve per kilogram of body weight (WCI65%HRreserve/kg) was very high (ICC=.96, P<.001), indicating that the fitness index can be estimated without measuring the resting heart rate. PWC75%/kg decreased as age increased. The average PWC75%/kg was significantly higher in men than in women (P<.001), and in active than in inactive subjects (P<.01).ConclusionsThis study presents a new fitness index, the PWC75%/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 PWC75%/kg obtained from healthy men and women.