Objective To determine the association between cardiorespiratory fitness and sedentary behavior, independent of exercise activity. Patients and Methods We included 2223 participants (aged 12-49 years; 1053 females [47%]) without known heart disease who had both cardiovascular fitness testing and at least 1 day of accelerometer data from the National Health and Nutrition Examination Survey 2003-2004. From accelerometer data, we quantified bouts of exercise as mean minutes per day for each participant. Sedentary time was defined as less than 100 counts per minute in mean minutes per day. Cardiorespiratory fitness was derived from a submaximal exercise treadmill test. Multivariable-adjusted linear regression analyses were performed with fitness as the dependent variable. Models were stratified by sex, adjusted for age, body mass index, and wear time, and included sedentary and exercise time. Results An additional hour of daily exercise activity time was associated with a 0.88 (0.37-1.39; P<.001) metabolic equivalent of task (MET) higher fitness for men and a 1.37 (0.43-2.31; P=.004) MET higher fitness for women. An additional hour of sedentary time was associated with a -0.12 (-0.02 to -0.22; P=.03) and a -0.24 (-0.10 to -0.38; P<.001) MET difference in fitness for men and women, respectively. Conclusion After adjustment for exercise activity, sedentary behavior appears to have an inverse association with fitness. These findings suggest that the risk related to sedentary behavior might be mediated, in part, through lower fitness levels.
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