Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Page number: 1635-1642
Background: Protein ingestion after exercise has consistently shown to increase muscle protein synthesis. There is some evidence that protein before/during exercise is beneficial during resistance exercise, since protein synthesis can occur in between sets, but it is not certain if this benefit applies to endurance exercise.
Hypothesis: Protein ingestion during endurance exercise will decrease protein breakdown during exercise and enhance recovery after exercise.
Subjects: Eight healthy men who exercise at least 3 times per week, age 22.6 ± 0.8 y
Experimental design: randomized, counterbalanced, cross-over
Protocol : Alumni from a midwestern university were asked to complete a questionnaire regarding social demographics, current exercise frequency, current dietary patterns, and cognitive health.
Treatments : CHO: a carbohydrate beverage (90 g/L glucose) or CHO+PRO: a carbohydrate + protein beverage (90 g/L glucose + 30 g/L whey protein).
Protocol :Subjects were first evaluated for VO2max and Wmax on a stationary bicycle. They reported to the laboratory for 2 testing days, for the 2 experimental beverages, separated by 1-2 wks. Each testing session was divided into rest (2 hrs), exercise (3 hrs), and recovery (3 hrs) periods. First, intravenous catheters were inserted into the femoral artery and vein (leg) and in the antecubital vein (arm). Then, a primed, constant infusion of isotopically labeled phenylalanine was started. This phenylalanine functions equivalently to the unlabeled phenylalanine, but it can be distinguished from the commonly occurring amino acid. The isotopes were allowed 2 hrs to equilibrate (rest period). When the exercise session began, they consumed 5 mL/kg body weight of the test beverage (399 ± 20 mL). The subjects cycled for 3 hrs at 55% of their previously determined Wmax (60 ± 1% VO 2max). They consumed 2.5 mL/kg of the test beverage every 30 min through the exercise and the recovery (3 hrs) stages. Femoral arterial and venous blood samples were acquired at 90, 105, and 120 min after the start of the infusion and every 30 min during exercise and recovery. After each of the rest, exercise, and recovery periods, a muscle biopsy was taken from the vastus lateralis to assess rates of fractional protein synthesis (FSR, incorporation of the labeled phenylalanine into muscle tissue).
The continuous usage of the vastus lateralis muscles during endurance exercise does not allow for protein synthesis during exercise. However, protein supplementation is extremely helpful in recovery. Protein does not appear to be detrimental to exercise performance, however, so it may be of some advantage to consume protein during exercise so that it is already in the blood stream after exercise and can be utilized as soon as the exercise terminates. The findings of this study agree well with multiple other studies showing the benefits of carbohydrate and protein feeding during the postexercise period for muscle recovery.