Protein-leucine ingestion following strenuous endurance exercise accentuates muscle protein synthesis and improves recovery of muscle performance.
Purpose: To determine if a low-dose protein-leucine blend ingested following endurance exercise enhances skeletal muscle myofibrillar protein fractional synthetic rate (FSR).
Method: In a crossover design, twelve trained men completed 100 min of high-intensity cycling, then ingested either 70/15/180/30g protein/leucine/carbohydrate/fat (15LEU), 23/5/180/30g (5LEU) or 0/0/274/30g (CON) beverages in randomised order in 4 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-13C6]phenylalanine incorporation and mTORC1-pathway phosphorylation by Western blot.Results
The 33% (90%CL +/-12%) increase in FSR with 5LEU (mean, SD, 0.080, 0.014%[middle dot]h-1) vs. CON (0.060, 0.012%[middle dot]h-1) represented near-maximal FSR stimulation. Tripling protein-leucine dose (15LEU, 0.090, 0.11%[middle dot]h-1) negligibly increased FSR (13% +/-12% vs. 5LEU). Despite similar FSR, mTORC1Ser2448 phosphorylation only increased with 15LEU at 30-min, whereas p70S6KThr389, rpS6Ser240/244, and 4E-BP1[gamma]Ser112 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 vs 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.
Conclusion: Ingesting 23 g of protein with 5 g 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.
(C) 2014 American College of Sports Medicine