Prolonged Bouts Of Sedentary Behavior Are Associated With Cardiorespiratory Fitness In Young Adults

Growing evidence suggests an association between total sedentary time and cardiorespiratory fitness (CRF), a key cardiometabolic disease risk factor. However, the impact of prolonged bouts of sedentary behavior on CRF, particularly in young adults, is less understood. PURPOSE: To determine the associations between prolonged bouts of sedentary behavior and CRF in young adults. METHODS: 95 men (n = 39) and women (n = 56) participated in the study (mean ± SD: age 19.9 ± 1.4 y; BMI 23.9 ± 2.9 kg/m2; and VO2peak 47.1 ± 7.6 mL/kg/min). Sedentary behavior (<150 counts/min) and moderate-to-vigorous physical activity (MVPA, >2689 counts/min) were measured by an accelerometer worn for 7 consecutive days. Sedentary bouts were defined as greater than or equal to 20, 30 and 60 min. CRF was measured during a progressive treadmill test. Multivariable regression analyses were used to assess associations between variables, while controlling for age, accelerometer wear time, and MVPA. RESULTS: Total time spent in sedentary behaviors averaged 8.4 ± 1.5 h/day. Sedentary bouts of 20, 30 and 60 min or more accounted for 28%, 16%, and 3% of total sedentary time, respectively. The average length for bouts of 20, 30, and 60 min or more was 31.8 ± 3.8 min, 45.5 ± 6.9 min and 76.6 ± 12.4 min, respectively, with 34% of participants not engaging in bouts of 60 min or more. Sedentary bouts of 20 min or more had the strongest associations with CRF, compared to bouts of 30 and 60 min or more. After adjustment for all covariates, total time spent in sedentary bouts of 20 min or more was independently associated with CRF (β = -0.32, p < 0.01). Similarly, time spent in sedentary bouts of 30 min or more was independently associated with CRF (β = -0.28, p < 0.01). Time spent in sedentary bouts of 60 min or more was not associated with CRF (β = -0.20, p = 0.05). CONCLUSIONS: Our novel findings suggest that sedentary behavior, in bouts of 20 min or more, is significantly and independently associated with CRF young adults. These results suggest CRF as a potential mechanism linking sedentary behavior to cardiometabolic disease risk. These findings have important implications for cardiometabolic disease prevention programs for young adults and suggest that public health guidelines with regards to minimizing prolonged sedentary behaviors are warranted. Supported by: NIH 1U54GM104944