No abstract

For comparisons of cardiopulmonary fitness across different categories of body mass, the lean mass-ratio standard should be used.

OBJECTIVE: Cardiorespiratory fitness is currently estimated by dividing maximal oxygen consumption (VO 2max ) by body weight (per-weight standard). However, the statistically correct way to neutralize the effect of weight on VO 2max in a given population is adjustment for body weight by regression techniques (adjusted standard). Our objective is to quantify the bias introduced by the per-weight standard in a population distributed across different categories of body mass. DESIGN: This is a cross-sectional study. SUBJECTS AND METHODS: Baseline measures from participants of the Dose-Responses to Exercise Training Study (DR's EXTRA), 635 men (body mass index (BMI): 19--47 kg m À2 ) and 638 women (BMI: 16--49 kg m À2 ) aged 57--78 years who performed oral glucose tolerance tests and maximal exercise stress tests with direct measurement of VO 2max . We compare the increase in VO 2max implied by the per-weight standard with the real increase of VO 2max per kg body weight. A linear logistic regression model estimates odds for abnormal glucose metabolism (either impaired fasting glycemia or impaired glucose tolerance or Type 2 diabetes) of the least-fit versus most-fit quartile according to both per-weight standard and adjusted standard. RESULTS: The per-weight standard implies an increase of VO 2max with 20.9 ml min À1 in women and 26.4 ml min À1 in men per additional kg body weight. The true increase per kg is only 7.0 ml min À1 (95% confidence interval: 5.3--8.8) and 8.0 ml min À1 (95% confidence interval: 5.3--10.7), respectively. Risk for abnormal glucose metabolism in the least-fit quartile of the population is overestimated by 52% if the per-weight standard is used. CONCLUSIONS: In comparisons across different categories of body mass, the per-weight standard systematically underestimates cardiorespiratory fitness in obese subjects. Use of the per-weight standard markedly inflates associations between poor fitness and co-morbidities of obesity.