ARTERIAL AND VENOUS AMINO ACID CONCENTRATIONS AND PROTEIN BALANCE AFTER A RESISTANCE TRAINING SESSION

Abstract

Increase in skeletal muscle size with resistance exercise training represents a fundamental biologic adaptation to an increased workload. Such hypertrophy results from changes in the rates of protein synthesis and/or breakdown. After a single resistance training session (RTS) both protein synthesis and protein breakdown occur and net balance is either positive or negative. PURPOSE: To assess the effects of RTS on arterial and venous free amino acid concentrations and protein balance in male subjects. METHODS: Both the exercise group (EG) and the control group (CG) consisted of six healthy physically active males. On the measurement day in fasting conditions stable isotopic tracer of L-[ring-2H5] phenylalanine was infused during the experiment and enrichment was analysed by GC/MS. EG started a heavy hypertrofic 50 minute RTS for lower extremities 55 minutes after infusion. At the same time CG was at rest. Blood samples were drawn from femoral artery and vein before infusion and at 135, 145, 155 and 165 and 270, 280, 290 and 300 minutes and muscles samples from the vastus lateralis muscle at 165 and 300 minutes after infusion. A three-compartment model was used for determination of leg muscle protein kinetics. Blood samples for amino acids (n = 18) were analysed by HPLC. Subjects recorded their dietary intake for 5 days and training for 2 weeks before the experiment day. RESULTS: There were no significant differences between the groups in the arterial and venous concentrations of all free amino acids. After RTS both protein synthesis and breakdown were greater (p < 0.05) in EG than in CG resulting in similar negative protein net balance in both groups (−23 ± 9 nmol phe min−1 100 ml leg volume−1 for EG and -21 ± 3 nmol phe min−1 100 ml leg volume−1 for CG). Dietary intake and training were similar in the groups. CONCLUSION: These results indicate that RTS induced in fasting conditions a similar response in protein net balance as occurred at rest. Simultaneously arterial and venous free amino acid concentrations were similar after RTS and at rest. Supported by TEKES 40721/00.