Enhanced Amino Acid Sensitivity of Myofibrillar Protein Synthesis Persists for up to 24 h after Resistance Exercise in Young Men

We aimed to determine whether an exercise manatee: enhancement of muscle protein synthesis to feeding persisted 24 n after resistance exercise. We also determined the impact of different exercise intensities (90% or 30% maximal strength) m contraction volume (work-matched to failure ) on the response at 24 h of recovery. Fifteen men (21 +/- 1 y, BMI - 24.1 +/- 0.8 kg . m(-2)) received a primed, constant infusion of L [ring-C-13(6)]phenylalane to measure:e muscle protein synthesis after protein feeding at rest (FED; 15 g whey protein) and 24 h after resistance exercise (EX-FED). Participants performed unilateral leg exercises: It 4 sets at 90% of maximal strength to failure (90FAIL); 21 30% work-matched to 90FAIL (30WM): or 31 30% to failure (30FAIL). Regardless of condition, rates of mixed muscle protein and sarcoplasmic protein synthesis were similarly stimulated at FED and EX-FED. In contrast, protein ingestion stimulated rates of myofbrilla protein synthesis above fasting rates by 0.016 +/- 0.002%/h and the response was enhanced 24 h after resistance exercise, hut only in the 90FAIL and 30FAIL conditions, by 0.038 = 0.012 and 0.041 +/- 0.010, respectively. Phosphoryation of protein kinase B on Ser473 was greater than FED at EX-FED only n 90FAIL, whereas phosphorylation of mammal an target of rapamycin on Ser2448 was significantly increased at EX-FED above FED only in the 30FAIL condition. Our results suggest that resistance exercise performed until failure confers a sensitizing effect on human skeletal muscle for at least 24 h that is specific to the myofibrillar protein fraction. J. Nutr. 141: 568 573, 2011.