Abstract
PURPOSE: To examine the effects of post-exercise protein ingestion on the magnitude of exercise-induced endurance training adaptation. METHODS: In a randomized parallel group design, 25 individuals (VO2max 55 + or - 6 ml[middot]kg-1[middot]min-1) completed 6 weeks of treadmill running (4 sessions per week; 70-75 % VO2max, 30-60 min per day, 4 days per week). Participants were randomly assigned to a group receiving a supplement containing carbohydrate (CHO; 1.6 g sucrose[middot]kg-1; n= 12) or carbohydrate-protein (CHO-P; 0.8 g sucrose[middot]kg-1 and 0.8 g whey protein hydrolysate[middot]kg-1; n=13) ingested immediately post-exercise and then 1 h later. Baseline and follow-up measurements included expired gas, blood, and muscle biopsy samples to determine markers of cardiovascular and intramuscular training adaptation. Data are mean + or - SD. RESULTS: Absolute and relative improvement in VO2max in response to training was not different between groups (0.2 + or - 0.2 L[middot]min-1 and 3 + or - 1 ml[middot]kg-1.min in CHO-P and CHO; p> 0.05). However, plasma albumin content increased following the intervention in the CHO-P (2.09 + or - 0.1 to 2.27 + or - 0.2 g[middot]kg-1; time x trial: p= 0.01) relative to CHO (2.08 + or - 0.1 to 2.08 + or - 0.1 g[middot]kg-1). There was no between-group effect on estimated plasma volume change; however, an increase in plasma volume was shown in CHO-P treatment (3.88 + or - 0.7 to 4.10 + or - 0.8 L; time: p= 0.03) relative to CHO (3.68 + or - 0.4 to 3.74 + or - 0.6; p> 0.05) following the intervention. No differences in the change in expression for several key metabolic genes related to mitochondrial biogenesis (e.g. TFAM, PPAR and PGC-1alpha) and carbohydrate/lipid metabolism (e.g. HK, GLUT4 and FABP) were observed between groups (p>0.05). CONCLUSION: The inclusion of protein in a post-exercise recovery supplement increases plasma albumin content when combined with 6 weeks of treadmill-based endurance training. Nevertheless, the magnitude of improvement in VO2max was not different between groups. Thus, the present findings suggest that post-exercise protein ingestion may be beneficial in amplifying cardiovascular, but not intramuscular training adaptation.