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1 Physical Therapy, University of Texas Medical Branch, Galveston, Texas, United States
2 Internal Medicine, University of Texas Medical Branch, Galveston, Texas, United States
3 Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas, United States
4 Surgery, University of Texas Medical Branch, United States
* To whom correspondence should be addressed. E-mail: blrasmus{at}utmb.edu.
We have recently shown that resistance exercise and ingestion of essential amino acids with carbohydrate (EAA+CHO) can independently stimulate mTOR signaling and muscle protein synthesis in humans. Providing an EAA+CHO solution post-exercise can further increase muscle protein synthesis. Therefore, we hypothesized that enhanced mTOR signaling may be responsible for the greater muscle protein synthesis when leucine enriched EAA+CHO are ingested during post-exercise recovery. Sixteen male subjects were randomized to one of two groups (Control or EAA+CHO). The EAA+CHO group ingested the nutrient solution 1 hr after resistance exercise. mTOR signaling was assessed by immunoblotting from repeated muscle biopsy samples. Mixed muscle fractional synthetic rate (FSR) was measured using stable isotope techniques. Muscle protein synthesis and 4E-BP1 phosphorylation during exercise were significantly reduced (P<0.05). Post-exercise FSR was elevated above baseline in both groups at 1 hr but was even further elevated in the EAA+CHO group at 2 hr post-exercise (P<0.05). Increased FSR was associated with enhanced phosphorylation of mTOR and S6K1 (P<0.05). Akt phosphorylation was elevated at 1 hr, returned to baseline by 2 hr in the Control group, but remained elevated in the EAA+CHO group (P<0.05). 4E-BP1 phosphorylation returned to baseline during recovery in Control but became elevated when EAA+CHO was ingested (P<0.05). eEF2 phosphorylation decreased at 1- and 2 hrs post-exercise to a similar extent in both groups (P<0.05). Our data suggest that enhanced activation of the mTOR signaling pathway is playing a role in the greater synthesis of muscle proteins when resistance exercise is followed by EAA+CHO ingestion.
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