Abstract P138: Association between Cardiovascular Fitness and Accelerometer-Derived Physical Activity and Sedentary Time in the General Population

Abstract

Objectives: Prior literature suggests that sedentary behavior may represent a risk factor that is independent of physical activity. The mechanism for this association remains poorly understood. We hypothesized that sedentary behavior might be inversely associated with cardiorespiratory fitness, independent of moderate and vigorous activity. Methods: We included 2,223 participants (ages 12-49 years, 47% female) without known heart disease who had both cardiovascular fitness testing and at least one valid day of accelerometer data from NHANES 2003-2004. From accelerometer data, we quantified bouts of exercise (at least 8 of 10 minutes above previously defined thresholds corresponding to moderate- or vigorous-intensity activity) as mean minutes of activity bouts per day for each participant. Sedentary time was defined as <100 counts per minute of wear time in mean minutes per day. VO2 max estimates were derived from a sub-maximal exercise treadmill test using measured heart rate responses to known levels of exercise workloads. Multivariable-adjusted linear regression analyses were performed with fitness as the dependent variable. Models were stratified by gender and adjusted for age, BMI, mean wear time and included both sedentary and moderate-vigorous activity time. Results: We observed that moderate and vigorous exercises levels were positively correlated to VO2 max (R=0.237, p<0.0001). Sedentary time was found to be inversely associated with VO2 max (R=-0.07, p=0.002). With each additional minute of moderate-vigorous activity, VO2 max increased by 0.05 ml/kg/min (p=0.001, men) and 0.08 ml/kg/min (p=0.004, women). For each additional minute of sedentary time, VO2 decreased by 0.01 ml/kg/min in both men (p=0.026) and women (p=0.001). Conclusions: After adjustment for moderate and vigorous activity, sedentary behavior appears to have a minor, inverse association with fitness. These findings suggest that the risk related to sedentary behavior might be mediated, in part, through lower fitness levels.