Randomized controlled trial investigating the experimental effects of reduced habitual physical activity on cardiometabolic profile

Physiology of sedentary behavior

Sedentary behaviors (SB) are characterized by low energy expenditure while in a sitting or reclining posture. Evidence relevant to understanding the physiology of SB can be derived from studies employing several experimental models: bed rest, immobilization, reduced step count, and reducing/interrupting prolonged SB. We examine the relevant physiological evidence relating to body weight and energy balance, intermediary metabolism, cardiovascular and respiratory systems, the musculoskeletal system, the central nervous system, and immunity and inflammatory responses. Excessive and prolonged SB can lead to insulin resistance, vascular dysfunction, shift in substrate use toward carbohydrate oxidation, shift in muscle fiber from oxidative to glycolytic type, reduced cardiorespiratory fitness, loss of muscle mass and strength and bone mass, and increased total body fat mass and visceral fat depot, blood lipid concentrations, and inflammation. Despite marked differences across individual studies, longer term interventions aimed at reducing/interrupting SB have resulted in small, albeit marginally clinically meaningful, benefits on body weight, waist circumference, percent body fat, fasting glucose, insulin, HbA1c and HDL concentrations, systolic blood pressure, and vascular function in adults and older adults. There is more limited evidence for other health-related outcomes and physiological systems and for children and adolescents. Future research should focus on the investigation of molecular and cellular mechanisms underpinning adaptations to increasing and reducing/interrupting SB and the necessary changes in SB and physical activity to impact physiological systems and overall health in diverse population groups.

Experimental Evaluation of the Joint Effects of Exercise and Sedentary Behavior on Cognitive Function

Background

The objective of this study was to evaluate the potential joint effects of sedentary behavior and exercise on cognitive function.

Methods

Participants (M_age = 20 yrs) were randomly assigned to one of three experimental groups. The No Exercise Group (n = 19) was instructed to reduce steps to less than 5000/day and were not allowed to exercise for one-week; the Reduced MVPA (moderate-to-vigorous PA) Group (n = 18) was instructed to reduce steps to less than 5000/day but exercised for 50% of their previously reported vigorous PA for one-week; and the Control Group (n = 20) maintained normal activity for one-week. Cognitive functions (via Stroop and Trail Making tasks) were assessed at baseline, post-intervention, and after one week of resumed normal activity for the intervention groups.

Results

Statistically significant main effects for time were observed for Stroop Congruent (F_time = 11.7, p < 0.001, η ² _p = 0.18), Stroop Incongruent (F_time = 19.4, p < 0.001, η ² _p = 0.26), Stroop Control (F_time = 54.4, p > 0.001, η ² _p = 0.50), Trail Making-A (F_time = 19.1, p < 0.001, η ² _p = 0.26) and Trail Making-B (F_time = 13.8, p < 0.001, η ² _p = 0.21) tasks. However, there were no statistically significant group x time interactions (all p's > 0.05) for any of the cognitive parameters.

Conclusion

These experimental findings do not suggest an interaction effect between sedentary behavior and physical activity on cognitive function.