Physiology of sedentary behavior

Abstract

Sedentary behaviors (SB) are characterized by a 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 towards 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 on 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.

Sitting Time Reduction and Blood Pressure in Older Adults

“…Sitting reduction through standing more and taking more frequent breaks from sitting may be a novel lifestyle strategy for improving BP and easier for older individuals with chronic conditions to incorporate into their daily life . Potential physiologic reasons for SBP reductions could include more frequent interruptions to the bent artery position, which could improve blood flow and vascular shear stress …”

Exercise breaks prevent attenuation in cerebrovascular function following an acute bout of uninterrupted sitting in healthy children

“…The reduced $${\dot Q_{{\mathrm{ICA}}}}$$ relative cerebrovascular reactivity to CO 2 and slower MCA velocity τ may reflect reductions in cortical activity and therefore cortical perfusion and oxygen delivery with sitting (Pinto et al., 2023). Although speculative, this may account for the regional differences we report.…”

Enhanced muscle activity during interrupted sitting improves glycemic control in overweight and obese men

“…17 Extended periods of muscle inactivity during uninterrupted sedentary behavior contribute to glucose intolerance through local muscle-contraction mechanisms. 18 On the other hand, engaging in diverse muscle activities during both endurance and resistance exercises has been shown to enhance glucose uptake through distinct local pathways. 19 These various patterns of muscle activity, including factors like duration, amplitude, and the absence of contraction, can be effectively measured using wearable electromyography (EMG) devices.…”

“…Extended periods of muscle inactivity during uninterrupted sedentary behavior contribute to glucose intolerance through local muscle‐contraction mechanisms 18 . On the other hand, engaging in diverse muscle activities during both endurance and resistance exercises has been shown to enhance glucose uptake through distinct local pathways 19 .…”