Surrogate Measures of Physical Activity and Physical Fitness

Studies on physical activity, physical fitness, and health have been hampered because of invalid, unreliable, or impractical measures of physical activity. This report examines the validity of sedentary traits (resting tachycardia, obesity, and low vital capacity) as predictors of physical fitness as assessed by a maximal treadmill exercise test. Study participants were women (n = 3,943) and men (n = 15,627) with at least one visit to the Cooper Clinic in Dallas, Texas. Association of the sedentary traits with physical fitness was examined by multiple regression analyses. Sedentary traits were associated with physical fitness in all age and sex groups, accounting for 12-40% of the variance in treadmill time. When smoking, a simple physical activity index, and sedentary traits were included in a model to predict physical fitness, R2 values ranged from 0.20 to 0.53 in women and 0.45 to 0.61 in men and were significant at p less than 0.0001. These models account for approximately twice as much variance in physical fitness as has been reported previously. The addition of sedentary traits measurements to a simple physical activity index provides a valid estimate of physical fitness in epidemiologic studies.