Mixed
Disuse-induced muscle atrophy in humans is primarily driven by a sustained reduction in muscle protein synthesis (MPS) rather than an increase in muscle protein breakdown (MPB).
To prevent muscle loss during periods of inactivity (like injury recovery or bed rest), simply moving minimally is often insufficient to maintain normal synthesis rates. The primary driver of atrophy is the shutdown of muscle building processes. While you cannot always force training, understanding that synthesis drops significantly (40-50%) highlights why even minimal, involuntary movement or specific nutritional strategies (like amino acid provision, though noted as blunted) are critical to counteract this specific metabolic shutdown.
The amount of contractile activity required to offset this decline is decidedly minimal... The stereotypical finding in simple disuse-induced atrophy in humans is that there are reductions in both the fasted-state and fed-state MPS... Mathematical estimates suggest that it appears unlikely that rates of MPB contribute appreciably to disuse-induced muscle atrophy in humans.
Why this rating
Based on multiple human clinical studies (bed rest, immobilization) showing reproducible MPS suppression, though direct MPB measurements are noted as lacking.
Source
Control of skeletal muscle atrophy in response to disuse: clinical/preclinical contentions and fallacies of evidence
Philip J. Atherton et al. · American Journal of Physiology-Endocrinology and Metabolism · 2016
DOI 10.1152/ajpendo.00257.2016
More from this paper
- Immobilization induces rapid muscle insulin resistance (MIR) within 3-5 days, which may contribute to the dysregulation of protein metabolism, although a direct causal link to atrophy is not fully established.Good
- In preclinical rodent models, disuse atrophy involves both decreased protein synthesis and increased protein degradation, with the extent of degradation being muscle-specific and dependent on fiber type.Good
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