Comparing self-reported physical activity and sedentary time to objective fitness measures in a military cohort

Objectives: Regular vigorous physical activity (PA) and high levels of physical fitness (PF) confer health benefits. Conversely, sedentary time is a risk factor for chronic illness, independent of PA. We evaluated associations between self-reported PA, sedentary time, and objective PF measures in military Service members. Design: Cross-sectional study including 10,105 Air Force Millennium Cohort participants with a valid physical fitness assessment (PFA). Methods: Linear regression assessed associations between self-report PA, screen time, and usual activity and abdominal circumference (AC) and VO₂ max; logistic regression was used for PFA failure. We stratified by age and sex. Results: Men who self-reported high versus low levels of PA had greater AC (19–29 years: β = 0.23 in., 95% CI 0.07, 0.39; 30–39 years: β = 0.45 in., 95% CI 0.17, 0.72). High versus low self-reported PA was also associated with greater VO₂Max (β =: 0.81–1.41 mL/kg/min). Self-reported strength training for ≥2 days/week was associated with greater VO₂Max in 19–29 year old men (β = 0.84 mL/kg/min, 95% CI 0.09, 0.60) and 30–39 year old women (β = 0.74 mL/kg/min, 95% CI 0.02, 1.46). For younger men and women,<2 h of screen time/day was associated with greater VO₂Max (Males 19–29 years: β = 0.23 mL/kg/min, 95% CI 0.44, 1.26; Females 19–29 years: β = 0.83 mL/kg/min, 95% CI 0.25, 1.42). PA was not associated with PFA failure, while screen time was (Males OR: 0.32–0.65, 95% CI 0.17–0.92, p < 0.001–0.016). Conclusions: Self-reported PA and screen time were associated with some objective PF measures, including VO₂Max and AC. However, screen time alone was associated with PFA failure.