Lack of regular physical exercise or too much inactivity.

PURPOSE OF REVIEW: To discuss the current data that acute periods of physical inactivity are harmful to health. RECENT
FINDINGS: Bed rest prescribed for recovery from clinical conditions causes changes in thousands of mRNAs in leg muscles within days. Humans genetically more susceptible to metabolic disorders (low birth weight babies and type 2 diabetic offspring) are as, or more, susceptible to further metabolic dysfunction by the environmental perturbation of bed rest, as compared with healthy controls without these risk factors. High daily accumulations of sitting are not only associated with enhanced metabolic risk, but current findings report that increased sitting time leads to a reduction in insulin sensitivity. Reductions in walking or in ambulatory activity (lower step numbers taken by healthy humans) reduce insulin sensitivity and insulin signaling through Akt in skeletal muscle.
SUMMARY: New findings using human models of physical inactivity (bed rest, increased sitting time, and reduced daily ambulatory activity), extend pre-existing research showing that transitioning to physical inactivity rapidly reduced metabolic health. Modern technological advances that remove standing, walking, and major limb movement initiate metabolic dysfunctions that likely play a fundamental role in the development of obesity and type 2 diabetes.