The Effects Of Reducing Sedentary Behavior On Cardiorespiratory Fitness: A Six- month Randomized Controlled Trial

PURPOSE: Poor cardiorespiratory fitness (CRF) is associated with adverse health outcomes. Previous observational and cross-sectional studies have suggested that reducing sedentary behavior (SB) might improve CRF. Therefore, we investigated the effects of a six-month intervention of reducing SB on CRF in 64 sedentary inactive adults with metabolic syndrome in a randomized controlled trial. METHODS: In the intervention group (INT, n = 33) the aim was to reduce SB by 1 h/day without increasing exercise training. Control group (CON, n = 31) was instructed to maintain their habitual SB and physical activity (PA). Maximal oxygen uptake (VO2max) and maximal power output (Wmax) were measured by maximal graded bicycle ergometer test with respiratory gas measurements. PA and SB were measured during the whole intervention using accelerometers. Linear mixed models were used to analyze intervention effects, and Pearson’s correlation was used to assess the associations between the changes in accelerometry variables and CRF during the intervention in the whole study group. RESULTS: During the six months, the INT group reduced SB by 40 min/day while the CON group maintained baseline levels. Moderate-to-vigorous PA replaced half of the SB, and the rest was replaced by light PA and standing. Furthermore, step count increased in both groups (INT 3300 vs. CON 1600 per day, group x time p = 0.001). The intervention did not affect VO2max (group x time p > 0.05). Absolute Wmax did not differ between groups but increased in INT compared to CON when scaled to fat free mass (FFM) (Wmax/kgFFM at six months INT 1.54 [95 % CI: 1.41, 1.67] vs. CON 1.45 [1.32, 1.59], group x time p = 0.036). Finally, the changes in daily step count during the intervention correlated positively with the changes in VO2max scaled to body mass and FFM (r = 0.31 and 0.30, respectively, p < 0.05) in the whole study group. CONCLUSIONS: Reducing SB without adding exercise training does not seem to improve VO2max in adults with metabolic syndrome. However, succeeding in increasing daily step count may increase VO2max.