Journal Title (Medline/Pubmed accepted abbreviation): J Nutr Sci Vitaminol
Page numbers: 255-259
Background:High-protein snacks ingested 3 hours after a meal elevate the blood concentration of branched-chain amino acids (BCAAs). Muscle uptake and utilization of amino acids may contribute to increases in both mass and strength. However, resistance exercise produces reduced blood flow to various muscles followed by an increased blood volume to the muscles between exercise sets. Therefore, blood volume fluctuation may control the efficacy of amino acid uptake by the muscles.
Hypothesis/purpose of study:To investigate the effects of different blood volume fluctuation times on the efficiency of amino acid utilization and BCAA and glucose plasma concentrations.
Subjects:8 healthy adults (3 men and 5 women) participated in this study (age, 24.5 ± 4.6 yr; height, 168.1 ± 7.6 cm; weight, 58.7 ± 7.6 kg; body mass index, 20.7 ± 1.2 kg/m2).
Experimental design: Randomized, cross-over study
Treatments and protocol:Participants were randomized to either a high number of exercise repetitions with long intervals (HL) or a low number of repetitions with a short interval (LS). Each group crossed over to the other type of exercise following a 7-day interval. A standardized meal was provided 3 hours before the high-protein snack (dried egg white [51 kcal/14.5 g], gelatin [2.5 g], sugar [18 g], and water; total of 15 g protein and 130 kcal). The resistance exercise started 1 hour after snack ingestion and consisted of 135 total slow arm flex/extensions over 15 minutes (HL, 9 sets of 15 repetitions with 10-sec rest intervals; LS, 27 sets of 5 repetitions with 3- to 4-sec rest intervals). Blood samples for BCAA and glucose concentrations were collected before snack ingestion and at 60 and 90 minutes after snack ingestion. Blood volume to the antebrachial muscle, as reflected by total hemoglobin content of the muscle measured via infrared spectroscopy, was determined during the total exercise time.
The results of this study suggest that the pattern of blood volume fluctuations can influence the efficiency of amino acid uptake in muscles during resistance exercise. The higher frequency that blood volume returned to normal (typically 3 to 4 sec) in the LS group may have allowed increased amino acid uptake compared with the HL group. This was evidenced by the lack of increase in BCAA plasma concentration after the exercise sets in the LS group from the 60- to 90?minute time points. However, actual amino acid uptake by the muscle tissue was not measured to confirm utilization of the BCAA. It is not clear whether the lack of increase in plasma BCAA (and glucose as well) observed at the 90-minute time point for the LS group vs the HL group actually represented increased muscle uptake of these nutrients.