title: Enhanced amino acid sensitivity of myofibrillar protein synthesis persists for up to 24 h after resistance exercise in young men.
abstract: We aimed to determine whether an exercise-mediated enhancement of muscle protein synthesis to feeding persisted 24 h after resistance exercise. We also determined the impact of different exercise intensities (90% or 30% maximal strength) or contraction volume (work-matched or 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-(13)C(6)]phenylalanine to measure 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: 1) 4 sets at 90% of maximal strength to failure (90FAIL); 2) 30% work-matched to 90FAIL (30WM); or 3) 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 myofibrillar protein synthesis above fasting rates by 0.016 ± 0.002%/h and the response was enhanced 24 h after resistance exercise, but only in the 90FAIL and 30FAIL conditions, by 0.038 ± 0.012 and 0.041 ± 0.010, respectively. Phosphorylation of protein kinase B on Ser473 was greater than FED at EX-FED only in 90FAIL, whereas phosphorylation of mammalian 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.
authors.affiliation: Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Burd
authors.forename: Daniel W D
authors.initials: DW
authors.lastname: West
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Moore
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Atherton
authors.forename: Aaron W
authors.initials: AW
authors.lastname: Staples
authors.forename: Todd
authors.initials: T
authors.lastname: Prior
authors.forename: Jason E
authors.initials: JE
authors.lastname: Tang
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rennie
authors.forename: Steven K
authors.initials: SK
authors.lastname: Baker
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Phillips
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000328:Adult; D000596:Amino Acids / Q000378:metabolism*; D018797:Cell Cycle Proteins; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D009210:Myofibrils / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D055070:Resistance Training; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D055815:Young Adult
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D007328:Insulin; D009124:Muscle Proteins; D010750:Phosphoproteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa