Glucose intolerance and physical inactivity: The relative importance of low habitual energy expenditure and cardiorespiratory fitness

Glucose intolerance and diabetes mellitus are associated with physical inac tivity, but it is unclear whether preventive interventions should aim at in creasing overall energy expenditure or increasing participation in vigorous , fitness-enhancing activities. Studies aimed at separating and quantifying the effects of these two dimensions of physical activity should use well-v alidated measurement instruments and employ a study design in which the biv ariate error structure of these instruments is determined. In the Isle of E ly Study (Cambridgeshire, United Kingdom), 775 individuals aged 45-70 years in 1994-1997 completed a glucose tolerance test and assessment of 4-day ph ysical activity level (total energy expenditure/basal metabolic rate) by he art rate monitoring, a technique that has been validated against doubly lab eled water and whole-body calorimetry. Cardiorespiratory fitness (maximum o xygen uptake (VO2max) per kg)) was measured in a submaximal test. To correc t for measurement error, the authors had 190 individuals repeat both tests on three occasions at 4-month intervals. Two-hour glucose level was negativ ely correlated with physical activity level (men: r = -0.22, p < 0.001; wom en: r = -0.11, p < 0.05) and VO2max per kg (men: r = -0.18, p < 0.01; women : r = -0.19, p < 0.001) and was positively correlated with age and obesity. The model incorporating bivariate adjustment for measurement error showed that energy expenditure had a major effect on glucose tolerance, but there was less of an effect for cardiorespiratory fitness. These data provide sup port for public health strategies aimed at increasing overall energy expend iture.