title: Metabolic consequences of physical inactivity.
abstract: Physical inactivity is associated with alteration of normal physiologic processes leading to muscle atrophy, reduced exercise capacity, insulin resistance, and altered energy balance. Bed rest studies in human beings using stable isotopes of amino acids indicate that muscle unloading decreases the turnover rates of muscle and whole-body proteins, with a prevailing inhibition of protein synthesis. In the fasting state, muscle and whole-body nitrogen loss was not accelerated during bed rest. In experimental postprandial states, the amino acid-mediated stimulation of protein synthesis was impaired, whereas the ability of combined insulin and glucose infusion to decrease whole-body proteolysis was not affected by muscle inactivity. Thus, an impaired ability of protein/amino acid feeding to stimulate body protein synthesis is the major catabolic mechanism for the effect of bed rest on protein metabolism. This suggests that a protein intake level greater than normal could be required to achieve the same postprandial anabolic effect during muscle inactivity. Metabolic adaptation to muscle inactivity also involves development of resistance to the glucoregulatory action of insulin, decreased energy requirements, and increased insulin and leptin secretion. These alterations may lead to the development of the metabolic syndrome that is defined as the association of hyperinsulinemia, dyslipidemia, hypertension, hyperglycemia, and abdominal obesity. This cluster of metabolic abnormalities is a risk factor for coronary artery disease and stroke. Evidence indicates that exercise training programs may counteract all of these abnormalities both in healthy sedentary subjects and in patients affected by a variety of chronic disease states.
authors.affiliation: Department of Clinical, Morphological, and Technological Sciences, Division of Internal Medicine, University of Trieste, Trieste, Italy. biolo@units.it <biolo@units.it>
authors.forename: Gianni
authors.initials: G
authors.lastname: Biolo
authors.forename: Beniamino
authors.initials: B
authors.lastname: Ciocchi
authors.forename: Manuela
authors.initials: M
authors.lastname: Stulle
authors.forename: Arianna
authors.initials: A
authors.lastname: Piccoli
authors.forename: Stefania
authors.initials: S
authors.lastname: Lorenzon
authors.forename: Viviana
authors.initials: V
authors.lastname: Dal Mas
authors.forename: Rocco
authors.initials: R
authors.lastname: Barazzoni
authors.forename: Michela
authors.initials: M
authors.lastname: Zanetti
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Guarnieri
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001510:Bed Rest; D002318:Cardiovascular Diseases / Q000209:etiology; D004044:Dietary Proteins / Q000008:administration & dosage; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy; D006710:Homocysteine / Q000097:blood; D006801:Humans; D007333:Insulin Resistance; D024821:Metabolic Syndrome / Q000209:etiology; D008660:Metabolism / Q000502:physiology*; D008954:Models, Biological; D009124:Muscle Proteins / Q000378:metabolism; D009133:Muscular Atrophy / Q000209:etiology; D014176:Protein Biosynthesis; D012307:Risk Factors
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D009124:Muscle Proteins; D006710:Homocysteine