Hormonal
Skeletal muscle disuse (immobilization, bed rest, or unloading) causes rapid muscle atrophy primarily through a significant reduction in muscle protein synthesis (MPS), while muscle protein breakdown (MPB) remains largely unchanged or is not the primary driver.
If you are immobilized or unable to exercise (e.g., cast, bed rest), your muscles will stop building protein rapidly, leading to atrophy. You cannot simply 'wait it out' without loss. Focus on countermeasures like high-quality protein intake and any permitted mechanical loading (like electrical stimulation or isometric exercises) to mitigate the drop in muscle protein synthesis.
Crucially, blunting of MPS in response to muscle unloading is not restricted to fasted periods... available evidence strongly supports the notion that skeletal muscle atrophy in humans during a period of disuse is driven by blunting of both postabsorptive and postprandial MPS... rather than increases in MPB.
Why this rating
Based on multiple human clinical studies (bed rest, ULLS) showing consistent MPS reductions, though MPB measurements are technically challenging.
Source
Human Skeletal Muscle Disuse Atrophy: Effects on Muscle Protein Synthesis, Breakdown, and Insulin Resistance—A Qualitative Review
Supreeth Rudrappa et al. · Frontiers in Physiology · 2016
DOI 10.3389/fphys.2016.00361
More from this paper
- Muscle disuse induces muscle-specific insulin resistance (IR), which accelerates muscle mass loss, particularly in individuals with pre-existing Type 2 Diabetes.Good
- Disuse atrophy exhibits fiber-type specificity, with Type I (slow-twitch) fibers atrophying faster and to a greater degree than Type II (fast-twitch) fibers during prolonged disuse.Moderate
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