The Seated Inactivity Trial (S.I.T)

Abstract

Sedentary time, independent of physical activity levels, is a risk factor for several chronic diseases and all-cause mortality. The negative effects of extreme amounts of sedentary behavior have been examined (e.g., bed rest and detraining studies in fit individuals); however, more true-to-life trials are necessary to understand the health implications of increased sedentary time. PURPOSE: The objective of this study was to determine whether imposing ten hours of sedentary time per week for eight weeks would alter the cardiometabolic risk profile of physically active adults. METHODS: Sixteen healthy young adults (aged 21.6 ± 1.4 years, 10 males) who met physical activity guidelines (≥150 minutes moderate-to-vigorous physical activity/week) were randomized to either the sitting (SIT) group or no-intervention control (CON) group. SIT participants attended monitored sedentary sessions for eight weeks (10 hrs/week). Laboratory assessments at baseline, week four, and week eight included: blood pressure; body composition (DEXA scan); fasting blood samples; physical activity levels (seven days of accelerometry, via Actical at wrist); and three-day food records. RESULTS: SIT and CON participants were not different at baseline for cardiometabolic risk factors (p>0.05). Systolic blood pressure increased in SIT, but not CON, from baseline to week four (SIT: 10.1 ± 7.2 mmHg; CON: -7.3 ± 9.6 mmHg; p=0.001), and remained elevated at week eight. At week eight, there was a significant increase in total cholesterol from baseline for SIT (11.1 ± 12.5 mg/dL, p<0.05), but not CON (1.1 ± 22.2 mg/dL, p>0.05), with no between-group differences. The change in systolic blood pressure was associated with a change in total cholesterol (r=0.51, p=0.04). There were no changes in fasting glucose or body composition. Physical activity did not change, but SIT participants decreased caloric intake from baseline to week eight (p<0.05). CONCLUSION: Following eight weeks of imposed sedentary time, physically active adults increased systolic blood pressure and total cholesterol, but did not exhibit changes in other risk factors. Imposing just 10 hours per week of sedentary behavior appeared to have an adverse impact on cardiometabolic health in physically active adults.