Protein–Leucine Fed Dose Effects on Muscle Protein Synthesis after Endurance Exercise

• Published in: Medicine and science in sports and exercise 2015-03, Vol.47 (3), p.547-555
• Main Authors: ROWLANDS, DAVID S, NELSON, ANDRE R, PHILLIPS, STUART M, FAULKNER, JAMES A, CLARKE, JIM, BURD, NICHOLAS A, MOORE, DANIEL, STELLINGWERFF, TRENT
• Format: Article
• Language: English
• Subjects: Adult; Amino Acids, Essential - blood; Beverages; Blood Glucose - metabolism; Cross-Over Studies; Dietary Carbohydrates - administration & dosage; Dietary Fats - administration & dosage; Dietary Proteins - administration & dosage; Dietary Proteins - metabolism; Humans; Insulin - blood; Leucine - administration & dosage; Leucine - blood; Male; Mechanistic Target of Rapamycin Complex 1; Multiprotein Complexes - metabolism; Muscle Proteins - biosynthesis; Muscle, Skeletal - metabolism; Myofibrils - metabolism; Physical Endurance - physiology; Single-Blind Method; TOR Serine-Threonine Kinases - metabolism
• ISSN: 0195-9131; 1530-0315
• DOI: 10.1249/MSS.0000000000000447

Protein–leucine ingestion after strenuous endurance exercise accentuates muscle protein synthesis and improves recovery of muscle performance. PURPOSEThe objective of this study is to determine whether a low-dose protein–leucine blend ingested after endurance exercise enhances skeletal muscle myofibrillar protein fractional synthetic rate (FSR). METHODIn a crossover design, 12 trained men completed 100 min of high-intensity cycling, then ingested either 70/15/180/30 g of protein/leucine/carbohydrate/fat (15LEU), 23/5/180/30 g of 5LEU, or 0/0/274/30 g of CON beverages in randomized order in four servings during the first 90 min of a 240-min recovery period. Muscle biopsies were collected at 30 and 240 min into recovery with FSR determined by L-[ring-C6]phenylalanine incorporation and mTORC1 pathway phosphorylation by Western blot. RESULTSThe 33% (90% CL, ±12%) increase in FSR with 5LEU (mean, SD0.080, 0.014%·h) versus CON (0.060, 0.012%·h) represented near-maximal FSR stimulation. Tripling protein–leucine dose (15LEU0.090, 0.11%·h) negligibly increased FSR (13%, ±12% vs 5LEU). Despite similar FSR, mTORC1 phosphorylation only increased with 15LEU at 30 min, whereas p70S6K, rpS6, and 4E-BP1γ phosphorylation increased with protein–leucine quantity at one or both time points. Plasma leucine and essential amino acid concentrations decreased during recovery in CON but increased with protein–leucine dose. Serum insulin was increased in 15LEU versus CON (60%, ±20%) but was unaffected relative to 5LEU. Regression analysis revealed p70S6K–rpS6 phosphorylation moderately predicted FSR, but the associations with plasma leucine and essential amino acids were small. CONCLUSIONSIngesting 23 g of protein with 5 g of added leucine achieved near-maximal FSR after endurance exercise, an effect unlikely attributable to mTORC1–S6K–rpS6 signaling, insulin, or amino acids. Translating the effects of protein–leucine quantity on protein synthesis to optimizing adaptation and performance requires further research.