Sedentarismo y salud muscular

Sedentary behavior is an independent determinant of cardiometabolic risk and should be distinguished from physical inactivity. While sedentary behavior is defined as waking hours spent sitting or reclining with an energy expenditure ≤1.5 METs, physical inactivity corresponds to non-compliance with exercise recommendations. Consequently, an individual can achieve physical activity goals and simultaneously remain exposed to prolonged periods of sedentary behavior, with adverse physiological effects that are not fully reversed by planned exercise. Skeletal muscle is the primary effector organ of sedentary behavior. The sustained reduction in muscle contractions decreases blood flow and metabolic activity, promoting loss of muscle mass and strength, reduced mitochondrial oxidative capacity, and a shift in the phenotype from oxidative fibers to predominantly glycolytic fibers. These modifications are accompanied by a decrease in lipoprotein lipase activity and other mechanisms involved in lipid metabolism, as well as a reduction in myokines with anti-inflammatory properties, favoring a state of chronic low-grade inflammation and increased visceral adiposity. From a metabolic standpoint, muscle disuse induces a rapid decrease in insulin sensitivity, with reduced GLUT-4-mediated glucose uptake, increased postprandial glucose and insulin levels, and a greater risk of developing type 2 diabetes. Furthermore, sedentary behavior is associated with alterations in cerebral perfusion and potential adverse effects on central nervous system function, possibly mediated by vascular and inflammatory mechanisms. Experimental evidence demonstrates that interrupting sedentary time with brief active breaks, approximately 2 to 3 minutes every 20–30 minutes, improves the postprandial glycemic and insulin response, promotes vascular function, and increases energy expenditure. Taken together, these findings support a paradigm shift in health recommendations: in addition to promoting regular exercise, it is necessary to reduce sedentary time and incorporate frequent breaks from sitting as a complementary strategy to preserve muscle health and decrease cardiometabolic risk.