Effects of reducing sedentary behavior on cardiorespiratory fitness in adults with metabolic syndrome: A 6-month RCT

Introduction: 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 6-month intervention of reducing SB on CRF in 64 sedentary inactive adults with metabolic syndrome in a non-blind randomized controlled trial.

Materials and methods: In the intervention group (INT, n = 33), the aim was to reduce SB by 1 h/day for 6 months without increasing exercise training. Control group (CON, n = 31) was instructed to maintain their habitual SB and physical activity. Maximal oxygen uptake (VO_2max ) was measured by maximal graded bicycle ergometer test with respiratory gas measurements. Physical activity and SB were measured during the whole intervention using accelerometers.

Results: Reduction in SB did not improve VO_2max statistically significantly (group × time p > 0.05). Maximal absolute power output (W_max ) did not improve significantly but increased in INT compared to CON when scaled to fat free mass (FFM) (at 6 months INT 1.54 [95% CI: 1.41, 1.67] vs. CON 1.45 [1.32, 1.59] W_max /kg_FFM , p = 0.036). Finally, the changes in daily step count correlated positively with the changes in VO_2max scaled to body mass and FFM (r = 0.31 and 0.30, respectively, p < 0.05).

Discussion: Reducing SB without adding exercise training does not seem to improve VO_2max in adults with metabolic syndrome. However, succeeding in increasing daily step count may increase VO_2max .