Research Review By Christopher Howard©

Date Posted:

October 2009

Study Title:

Essential amino acid and carbohydrate ingestion before resistance exercise does not enhance postexercise muscle protein synthesis

Authors:

Fujita S, Dreyer HC, Drummond MJ et al.

Author's Affiliations:

Departments of Internal Medicine and Physical Therapy, and Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas

Publication Information:

Journal of Applied Physiology 2009; 106: 1730–1739.

Background Information:

Acute resistance training stimulates muscle protein synthesis within 4 hours (1) and maintains that increased rate of protein synthesis for 24 to 48 hours (2). In addition, resistance training of 1-12 weeks duration increases basal rates of protein synthesis (3). Certain nutrients, primarily leucine and other essential amino acids (EAA), can be considered anabolic due to their effect on muscle protein synthesis (4). If carbohydrate (CHO) is added to an EAA solution, insulin secretion is increased. It has been well documented that insulin stimulates muscle protein synthesis, which is dependent on the availability of amino acids (5).

Supplementation with EAAs with or without CHO following resistance exercise increases the rate of muscle protein synthesis. In addition, supplementation with whole proteins, such as whey or casein, during the post-exercise time period has been shown to increase muscle protein synthesis. However, it is currently unclear whether supplementation with EAAs and CHO during the pre-exercise window will further increase post-exercise muscle protein synthesis.

The goal of this study was to support or refute the hypothesis that a leucine-enriched EAA and CHO solution consumed before exercise would prevent the exercise induced decrease in muscle protein synthesis and enhance muscle protein synthesis during the early post-exercise recovery period.

Pertinent Results:

Blood Flow, Insulin, and Glucose Uptake:
Leg blood flow increased significantly in both the EAA + CHO and Fasting groups during the exercise time period (p < 0.05). In both groups, leg blood flow returned to baseline values at 1 and 2 h post-exercise. Insulin levels were higher in the EAA + CHO group at the pre-exercise time period (p < 0.05) and remained higher during the exercise time period when compared to the fasting group (p < 0.05). Insulin concentration returned to baseline at 1 and 2 h post-exercise and was not different between groups. Glucose uptake was elevated in the pre-exercise time period for the EAA + CHO group compared to the fasting group (p < 0.05). Both groups had elevated glucose uptake during the exercise period when compared to the pre-exercise period (p < 0.05). The CHO + EAA group maintained an elevated glucose uptake at 1 hour post exercise. Both groups returned to baseline 2 h post-exercise.

Muscle Intracellular Leucine and Phenylalanine Concentrations:
At baseline, there was no difference between groups in either leucine or phenylalanine concentrations. Intracellular leucine and phenylalanine concentrations were elevated as a result of EAA + CHO ingestion and remained elevated from baseline during post-exercise, 1h post-exercise, and 2h post-exercise. In addition, intracellular leucine levels were elevated in the EAA + CHO group compared to the fasting group at pre-exercise, post-exercise, and 1h post-exercise. The same was true for phenylalanine except there was no difference between groups at 1-hour post-exercise. For both groups, levels remained elevated from baseline at 2h post-exercise.

Muscle Protein Synthesis and Phenylalanine Net Balance Across the Leg:
Muscle protein fractional synthetic rate (FSR) was significantly elevated pre-exercise in the EAA + CHO group compared to the fasting group. FSR in the EAA + CHO group returned to basal values during exercise (P > 0.05), remained unchanged during the 1 h post-exercise period (P > 0.05), and increased significantly at 2 h post-exercise (P < 0.05) compared with basal FSR. FSR decreased during exercise (p < 0.05) and increased during the 1 h and 2 h post-exercise periods (p > 0.05) for the fasting group. FSR was determined over the entire 2 h post-exercise recovery period and was found to be no different (p = .36) between the fasting and EAA + CHO groups. Blood phenylalanine concentration did not change for the fasting group, however it was significantly higher in the EAA + CHO group during the pre-exercise, exercise, and 1h post-exercise periods.

Clinical Application & Conclusions:

This study examined the effects of pre-exercise essential amino acid and carbohydrate ingestion on post-exercise markers of muscle protein synthesis. Based on the findings of this study, it is shown that pre-exercise consumption of specific EAA + CHO nutrients provided no benefit with regards to post-exercise muscle protein synthesis. As always, more research needs to be done in this area to further elucidate the details of why this occurs. In addition, just because pre-exercise ingestion of nutrients does not significantly impact muscle protein synthesis, other benefits exist. It is well known that consumption of carbohydrates prior to exercise helps delay the decrease in muscle glycogen content as well as having other favorable effects on exercise performance.

Study Methods:

Subjects:
  • Two groups of 22 young healthy subjects: Group 1 ? (6 male, 5 female) – consumed a solution of EAA + CHO 1h before performing a bout of heavy leg resistance exercise. Group 2 ? (7 male, 4 female) – performed the exact same resistance training but with no nutrient consumption.
  • All subjects were active but not currently engaged in resistance or endurance exercise program.
  • All women were not taking oral contraceptives and were in their follicular phase of the menstrual cycle.
Study Design:
  • On two separate occasions (> 5 days apart) and more than 5 days before conducting the study, each subject was tested for 1-RM on a leg extension machine (Cybex-VR2, Medway, MA) The higher of the two 1RM values was used to determine the starting weight (70% of 1RM) for the resistance exercise portion of the study.
  • On the second visit a dual-energy X-ray absorptiometry (DXA) scan (Hologic QDR 4500W, Bedford, MA) was performed to measure body composition and lean mass, and a pregnancy test was repeated in the female subjects.
  • Subjects were fed a standard dinner, and a snack was given at 22:00. The subjects completed an overnight fast and refrained from exercise for 24 h before the study. Catheters were inserted into a forearm vein for tracer infusion and in the femoral artery and vein of the leg for blood sampling. The femoral lines were placed in the same leg from which muscle biopsies were obtained. The arterial catheter was also used for the infusion of indocyanine green to determine blood flow.
  • Subjects were studied during four time periods: pre-exercise, exercise, first hour post-exercise, and second hour post-exercise. During the pre-exercise period, subjects in the EAA + CHO group ingested a nutrient solution, those in the fasting group did not.
  • Biopsies were taken at 1 hour pre-exercise, immediately pre-exercise, immediately post-exercise, 1 hour post-exercise, and 2 hours post-exercise. Blood samples were taken every 10 minutes during the pre-exercise, exercise, and post-exercise time periods.
  • The subjects performed 10 sets of 10 repetitions of leg extension exercises on a Cybex leg extension machine set to 70% of 1RM (for a few subjects this was lowered so as to achieve 10 repetitions per set). A rest period of 3 minutes was given between sets. Blood samples were taken immediately after the 3rd, 6th, 8th, and 10th sets.
Supplementation:
  • The nutrient solution contained leucine-enriched EAAs and CHO (surcrose).
  • The solution contained EAAs in the following proportions: histidine (8%), isoleucine (8%), leucine (35%), lysine (12%), methionine (3%), phenylalanine (14%), threonine (8%), and valine (10%).
  • Lean mass as determined by DXA was used to calculate the proportion of each EAA [0.35 g/kg of fat-free mass (FFM)] added to the nutrient solution. Similarly, CHO (sucrose) was added at 0.5 g/kg FFM to each nutrient solution.
Blood flow, Insulin, and Glucose Uptake:
  • Serum ICG concentration for the determination of leg blood flow was measured spectrophotometrically (Beckman Coulter, Fullerton, CA) at a wavelength of 805nm. Plasma glucose concentration was measured using an automated glucose and lactate analyzer (YSI, Yellow Springs, OH). Plasma insulin concentrations were determined by ELISA (LincoResearch, St. Charles, MO).
  • Muscle FSR: calculated the fractional synthetic rate of mixed muscle proteins (FSR) by measuring the incorporation rate of the phenylalanine tracer into the proteins
Statistical Analysis:
  • Primary outcomes were muscle protein synthesis, phenylalanine net balance, and blood metabolite and amino acid concentrations.
  • Secondary outcomes include intracellular signaling proteins and enzyme activity.
  • Comparisons between EAA + CHO and fasting were performed using ANOVA with repeated measures, the effects being group and time (Pre-Ex, Ex, 1 h Post-Ex, and 2 h Post-Ex), using JMP statistical software version 4.0.5 (SAS Institute). Post hoc testing was performed using t-test as appropriate. Significance was set at P < 0.05.

Study Strengths / Weaknesses:

Overall, this study was both well designed and well executed. All factors were well controlled. It is important to note that this study was completed on healthy but untrained individuals. It is unknown how this data relates to highly trained athletes who would probably benefit more from nutritional interventions.

Additional References:

  1. Biolo G, Maggi SP, Williams BD, Tipton KD, Wolfe RR. Increased rates of muscle protein turnover and amino acid transport after resistance exercise. Am J Physiol Endocrinol Metab 1995; 268: E514–E520.
  2. MacDougal JD, Gibala MJ, Tarnopolsky MA, MacDonald JR, Interisano SA, Yarasheski KE. The time course for elevated muscle protein synthesis following heavy resistance exercise. Can J Appl Physiol 1995; 20: 480–486.
  3. Yarasheski KE, Zachwieja JJ, Bier DM. Acute effects of resistance exercise on muscle protein synthesis rate in young and elderly men and women. Am J Physiol Endocrinol Metab 1993; 265: E210 –E214.
  4. Svanberg E, Moller-Loswick AC, Matthews DE, Korner U, Andersson M, Lundholm K. Effects of amino acids on synthesis and degradation of skeletal muscle proteins in humans. Am J Physiol Endocrinol Metab 1996; 271: E718–E724.
  5. Bell JA, Fujita S, Volpi E, Cadenas JG, Rasmussen BB. Short-term Insulin and nutritional energy provision do not stimulate muscle protein synthesis if blood amino acid availability decreases. Am J Physiol Endocrinol Metab 2005; 289: E999–E1006.