Two Weeks of Reduced Activity Decreases Leg Lean Mass and Induces “Anabolic Resistance” of Myofibrillar Protein Synthesis in Healthy Elderly
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Bibliographic record
Abstract
BACKGROUND: Alterations in muscle protein metabolism underlie age-related muscle atrophy. During periods of muscle disuse, muscle protein synthesis is blunted, and muscle atrophy occurs in young and old. The impact of a short reduction in physical activity on muscle protein metabolism in older adults is unknown. PURPOSE: The aim of this study was to investigate the impact of 14 days of reduced daily steps on fasted and fed-state rates of myofibrillar protein synthesis (MPS) to provide insight into the mechanisms for changes in muscle mass and markers of metabolic health. METHODS: Before and after 14 days of reduced daily step-count, 10 healthy older adults (age, 72 ± 1 y) underwent measures of insulin sensitivity, muscle strength, physical function, and body composition. Using a primed constant infusion of L-[ring-(13)C6]phenylalanine with serial muscle biopsies, basal, postabsorptive, and postprandial rates of MPS were determined before and after the 14-day intervention. RESULTS: Daily step-count was reduced by approximately 76% to 1413 ± 110 steps per day. Leg fat-free mass was reduced by approximately 3.9% (P < .001). Postabsorptive insulin resistance was increased by approximately 12%, and postprandial insulin sensitivity was reduced by approximately 43% after step reduction (P < .005). Concentrations of TNF-α and C-reactive protein were increased by approximately 12 and 25%, respectively, after step reduction (P < .05). Postprandial rates of MPS were reduced by approximately 26% after the intervention (P = .028), with no difference in postabsorptive rates. CONCLUSION: The present study demonstrates that 14 days of reduced steps in older adults induces small but measurable reductions in muscle mass that appear to be underpinned by reductions in postprandial MPS and are accompanied by impairments in insulin sensitivity and systemic inflammatory markers and postprandial MPS.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it