Physiology of physical inactivity, sedentary behaviours and non‐exercise activity: insights from the space bedrest model

Abstract

Physical inactivity, i.e., not reaching the recommended level of physical activity (PA) and sedentary behaviors (SB), i.e., sitting time have been associated with increased risk for common metabolic diseases. Recent epidemiological data suggest that high volumes of SB are detrimental for metabolic health, even in the presence of regular exercise, i.e., moderate/vigorous (MVPA). This suggests that the health effects of SB are independent from those of exercise. However, experimentally testing this hypothesis is complicated because of the difficulty in disassociating SB from PA. Bedrest studies, a traditional space science model, can offer new insights. In some bedrest studies, an exercise training protocol has been used to counteract the harmful effects of inactivity. While bedrest induces an inactive and sedentary state, exercise with bedrest represents a unique model of sedentary yet physically active people. Here, we review bedrest studies with and without exercise training.Although exercise training prevents the loss of muscle mass and function, even large volumes of exercise are not sufficient to fully counteract the negative metabolic adaptations triggered by inactivity. This observation supports the existence of independent adverse health effects of SB, but also the potential benefits of non-exercise activity, i.e., daily living light-intensity activities (LPA). We gathered available data to examine the complex relationships between exercise, non-exercise activity, SB and health outcomes. Given the large amount of SB in modern societies, the sole promotion of exercise, i.e., MVPA may be insufficient, and promotion of LPA may be a complimentary approach to improve health.

The Effects of Reduced Physical Activity on the Lipid Profile in Patients with High Cardiovascular Risk during COVID-19 Lockdown

“…It is important that doctors advise their patients to spend as little time as possible sitting and lying down and to engage in low-intensity physical activities. Even short intermittent bouts of walking during the day reduce glucose and insulin concentrations in the postprandial period, mostly with more potent effects observed in adults with overweight to obesity and diabetes mellitus [27].…”

The Effect of Obesity Class on the Energetics and Mechanics of Walking

“…Although increasing physical activity using walking and its associated higher NetC w/kg could be useful to shift individuals with obesity into the "regulated zone", in which appetite and food intake are affected by physical activity [44], the role of the latter in energy balance and weight loss remains controversial [44][45][46]. Nevertheless, decreasing the greater NetC w/kg in adults with obesity may be beneficial to increase non-exercise activity thermogenesis (NEAT) [11], and thus, light physical activity energy expenditure (1.6-2.9 metabolic equivalents; METs), which is inversely related to sedentary time [47] and has complementary effects to improve health [48].…”

Effects of long‐term simulated microgravity on liver metabolism in rhesus macaques

“…[62][63][64][65][66][67] In the short term, the liver metabolic functions were found either altered in response to sarcopenia (liver triglyceride accumulation) or suppressed (hepatic glucose output) by insulin. 67,68 In the long term, inflammation and other metabolic changes occurred in the liver, contributing to more advanced metabolic disorders. 19,69 One of the links between muscledependent (early phase) and muscle-independent (late phase) hepatic changes may lie in the intestine due to the bidirectional constant communications between the intestine and liver, intestine, and other organs (e.g., gutliver-muscle-brain axis 70 ).…”