Effects of 28 days of protein and amino acid supplementation and ankle immobilization on gastrocnemius muscle mass and strength and atrophy- and apoptosis-related gene expression in males.
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Purpose: The primary purpose was to determine the extent to which the daily supplementation of protein and amino acids for 28-days in combination with ankle immobilization in humans attenuated decreases in: 1) gastrocnemius muscle mass, 2) plantar flexion strength, 3) and expression of genes associated with the ubiquitin proteolytic pathway (UPS) and calcium-activated proteolytic system (CAS). A secondary purpose was to assess the safety of 28-days of protein and amino acid ingestion by evaluating whole blood and serum clinical chemistry markers. Methods: Twenty male participants wore a lower-limb immobilization boot for 28 days, consumed either a protein and amino acid supplement or an isocaloric carbohydrate placebo twice daily, and underwent testing at days 0, 14, and 28. Each testing session included hemodynamic measurements, blood collection, body composition analysis, lower leg girth and skinfold measurement, strength measurement, dietary analysis, and gastrocnemius muscle biopsies. The muscle tissue was analyzed for mRNA expression of ubiquitin, 20S-HC2, 20S-HC3, E2, E3, atrogin-1, MuRF1, calpain 1, calpain 2, myostatin, TNF-α, and NF-κB. Results: Lower-leg girth decreased over time (p = 0.020), and increased the expression of several genetic variables, but there were no significant changes in the body composition or strength variables (p > 0.05). All UPS, CAS, cytokine, and myostatin degenerative markers showed a significant increase over time (p < 0.05). However, significant interactions only occurred for E2 (time x group, p < 0.001) and E3 (time x group x leg, p > 0.016). Conclusion: The study showed no difference between groups for any of the genetic proeolytic markers, but indicated that several of these markers were increased in the immobilized and control legs. These changes may indicate a link between the UPS and TNF-α and NF-κB. Additionally, the results also indicated that myosatin may play a role in muscle astrophy induced by immobilization, instead of only disease and fasting.