Six healthy human subjects participated in two trials in
random order, PRE (EAC consumed immediately before exercise), and POST (EAC consumed
immediately after exercise).
A primed, continuous infusion of L-[ring-2H5]phenylalanine, femoral
arteriovenous catheterization, and muscle biopsies from the vastus lateralis were used to
determine phenylalanine concentrations, enrichments, and net uptake across the leg.
Blood andmuscle phenylalanine concentrations were increased by ~130% after drink consumption in both
trials. Amino acid delivery to the leg was increased during exercise and remained elevated for the
2 h after exercise in both trials.
Delivery of amino acids (amino acid concentration times blood
flow) was significantly greater in PRE than in POST during the exercise bout and in the 1st h after
exercise (P < 0.05).
Total net phenylalanine uptake across the leg was greater (P = 0.0002) during
PRE (209 ± 42 mg) than during POST (81 ± 19). Phenylalanine disappearance rate, an indicator
of muscle protein synthesis from blood amino acids, increased after EAC consumption in both
trials. These results indicate that the response of net muscle protein synthesis to consumption of
an EAC solution immediately before resistance exercise is greater than that when the solution is
consumed after exercise, primarily because of an increase in muscle protein synthesis as a result
of increased delivery of amino acids to the leg.