Protein intake does not increase vastus lateralis muscle protein synthesis during cycling

Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Year: 2011
Volume: 43
Number: 9
Page number: 1635-1642
doi: 10.1249/MSS.0b013e31821661ab

Summary of background and research design:

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).

Summary of research findings:
  • Arterial glucose and insulin peaked about 150 min into exercise and returned to baseline by the end of the exercise period.  Blood glucose was then elevated during the recovery period.
  • Insulin concentrations in the plasma were greater after exercise for both groups compared to before and during exercise, but higher for CHO+PRO than CHO.
  • At the whole leg level, consuming CHO+PRO during and after exercise increased protein synthesis relative to CHO alone.  Exercise greatly increased protein breakdown at the whole leg level compared with either rest or recovery, with no differences between treatments.  Net leg protein balance was negative during both rest and recovery for CHO alone.  For CHO+PRO, net leg protein balance was also still negative, although somewhat less so, during exercise, but was positive during the recovery period.
  • The FSR in the muscle that was most active (i.e., the vastus lateralis) was not affected with CHO+PRO vs. CHO alone in the during exercise feeding.  However, in the recovery period, the CHO+PRO increased the FSR to a greater degree than CHO alone.

Key practice applications:

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.

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