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Metabolic consequences of physical inactivity
Gianni Biolo1, Beniamino Ciocchi, Manuela Stulle
1Department of Clinical, Morphological, and Technological Sciences, Division of Internal Medicine, University of Trieste, Trieste, Italy. biolo@units.it <biolo@units.it>
Summary
Physical inactivity impairs protein synthesis, potentially requiring higher protein intake. Exercise training can reverse these negative metabolic changes, including insulin resistance and symptoms of metabolic syndrome.
Area of Science:
- Physiology
- Metabolic Science
- Exercise Science
Background:
- Physical inactivity leads to muscle atrophy, reduced exercise capacity, insulin resistance, and altered energy balance.
- Bed rest studies reveal that muscle unloading decreases protein turnover, primarily inhibiting protein synthesis.
- Metabolic adaptations include insulin resistance, decreased energy needs, and altered hormone secretion.
Purpose of the Study:
- To investigate the impact of muscle inactivity on protein metabolism and its relation to metabolic syndrome.
- To identify the catabolic mechanisms underlying the effects of bed rest on protein metabolism.
- To explore the potential of exercise to counteract these negative adaptations.
Main Methods:
- Utilized stable isotopes of amino acids in human bed rest studies.
- Examined protein synthesis and breakdown rates in fasting and postprandial states.
- Assessed metabolic adaptations including insulin sensitivity and hormone levels.
Main Results:
- Muscle inactivity impairs the postprandial stimulation of protein synthesis, suggesting a need for increased protein intake.
- Whole-body nitrogen loss was not accelerated during fasting bed rest.
- Insulin's ability to reduce proteolysis was unaffected by inactivity, but its glucoregulatory action showed resistance.
Conclusions:
- Impaired protein synthesis stimulation is a key catabolic mechanism during muscle inactivity.
- Increased protein intake may be necessary to maintain an anabolic state during inactivity.
- Exercise training is effective in reversing the adverse metabolic effects of inactivity, including insulin resistance and metabolic syndrome components.