PURPOSE: This study aimed to determine the effect of postexercise protein-leucine coingestion with CHO-lipid on subsequent high-intensity endurance performance and to investigate candidate mechanisms using stable isotope methods and metabolomics. METHODS: In this double-blind, randomized, crossover study, 12 male cyclists ingested a leucine/protein/CHO/fat supplement (LEUPRO 7.5/20/89/22 g•h -1, respectively) or isocaloric CHO/fat control (119/22 g•h -1) 1-3 h after exercise during a 6-d training block (intense intervals, recovery, repeated-sprint performance rides). Daily protein intake was clamped at 1.9 g•kg -1•d -1 (LEUPRO) and 1.5 g•kg -1•d -1 (control). Stable isotope infusions (1- 13C-leucine and 6,6- 2H 2-glucose), mass spectrometry-based metabolomics, and nitrogen balance methods were used to determine the effects of LEUPRO on whole-body branched-chain amino acid (BCAA) and glucose metabolism and protein turnover. RESULTS: After exercise, LEUPRO increased BCAA levels in plasma (2.6-fold; 90% confidence limits = ×/÷1.1) and urine (2.8-fold; ×/÷1.2) and increased products of BCAA metabolism plasma acylcarnitine C5 (3.0-fold; ×/÷0.9) and urinary leucine (3.6-fold; ×/÷1.3) and β-aminoisobutyrate (3.4-fold; ×/÷1.4) , indicating that ingesting ∼10 g leucine per hour during recovery exceeds the capacity to metabolize BCAA. Furthermore, LEUPRO increased leucine oxidation (5.6-fold; ×/÷1.1) and nonoxidative disposal (4.8-fold; ×/÷1.1) and left leucine balance positive relative to control. With the exception of day 1 (LEUPRO = 17 ± 20 mg N•kg -1, control =-90 ± 44 mg N•kg -1), subsequent (days 2-5) nitrogen balance was positive for both conditions (LEUPRO = 130 ± 110 mg N•kg -1, control = 111 ± 86 mg N•kg -1). Compared with control feeding, LEUPRO lowered the serum creatine kinase concentration by 21%-25% (90% confidence limits = ±14%), but the effect on sprint power was trivial (day 4 = 0.4% ± 1.0%, day 6 =-0.3% ± 1.0%). CONCLUSIONS: Postexercise protein-leucine supplementation saturates BCAA metabolism and attenuates tissue damage, but effects on subsequent intense endurance performance may be inconsequential under conditions of positive daily nitrogen balance.
Medicine and Science in Sports and Exercise / Vol. 44, No. 1, pp.57-68