Leucine for Muscle Protein Synthesis

Abstract

Background: The effects of essential amino acid (EAA) supplementation during moderate steady state (ie, endurance) exercise on postexercise skeletal muscle metabolism are not well described, and the potential role of supplemental leucine on muscle protein synthesis (MPS) and associated molecular responses remains to be elucidated.

Objective: This randomized crossover study examined whether EAA supplementation with 2 different concentrations of leucine affected post–steady state exercise MPS, whole-body protein turnover, and mammalian target of rapamycin 1 (mTORC1) intracellular signaling.

Design: Eight adults completed 2 separate bouts of cycle ergometry [60 min, 60% VO₂peak (peak oxygen uptake)]. Isonitrogenous (10 g EAA) drinks with different leucine contents [leucine-enriched (L)-EAA, 3.5 g leucine; EAA, 1.87 g leucine] were consumed during exercise. MPS and whole-body protein turnover were determined by using primed continuous infusions of [²H₅]phenylalanine and [1-¹³C]leucine. Multiplex and immunoblot analyses were used to quantify mTORC1 signaling.

Results: MPS was 33% greater (P < 0.05) after consumption of L-EAA (0.08 ± 0.01%/h) than after consumption of EAA (0.06 ± 0.01%/h). Whole-body protein breakdown and synthesis were lower (P < 0.05) and oxidation was greater (P < 0.05) after consumption of L-EAA than after consumption of EAA. Regardless of dietary treatment, multiplex analysis indicated that Akt and mammalian target of rapamycin phosphorylation were increased (P < 0.05) 30 min after exercise. Immunoblot analysis indicated that phosphorylation of ribosomal protein S6 and extracellular-signal regulated protein kinase increased (P < 0.05) and phosphorylation of eukaryotic elongation factor 2 decreased (P < 0.05) after exercise but was not affected by dietary treatment.

Conclusion: These findings suggest that increasing the concentration of leucine in an EAA supplement consumed during steady state exercise elicits a greater MPS response during recovery. 

http://ajcn.nutrition.org/content/94/3/809

It would be interesting to see the results if this were performed on strength/power athletes, for both max effort and CrossFit style training.  Most likely, leucine would be a good supplement to add for a competitive CrossFitter, but the difference between an athlete that's eating plenty of real meat anyway, and one who doesn't but supplements with leucine, would likely be small.