Journal Title (Medline/Pubmed accepted abbreviation): J. Strength Cond. Res.
Page numbers: 398-405
Summary of Background and Research Design
Background:Carnosine (β-alanyl-L-histidine) is a dipeptide (pair of 2 amino acids) that acts to buffer pH in skeletal muscle. Anserine (β-alanyl-1-methyl-L-histidine) is not present in human muscle but it is thought, when anserine is catabolized into β-alanine and methylhistidine, these compounds will be synthesized into carnosine in muscle. Resistance exercise increases hormones that act to both build (e.g. growth hormone, testosterone), and breakdown (e.g. cortisol) muscle protein, and catecholamine signaling molecules [e.g. adrenaline/epinephrine, adrenocorticotropic hormone (ACTH)] are also involved in these processes. Increased carnosine concentration is thought to make muscles more resistant to fatigue while attenuating the hormone response generated by intense resistance training.
Hypothesis: Supplementation with chicken breast meat extract (CBEX), that contains high concentrations of carnosine and anserine, for 30 days, will alter the hormone and molecular signaling response to resistance exercise.
Subjects:22 healthy men, age 25 ± 1, who were not involved in a regular training protocol
Experimental design:randomized, single-blinded, placebo-controlled design
Treatments:CBEX was made into a drink containing 0.6 g carnosine and 1.4 g anserine per 100 mL. Each day for 30 days, subjects drank 2 bottles (200 mL) of the CBEX beverage (total of 4 g carnosine and anserine) or a placebo (chicken flavored beverage containing no animal ingredients).
Protocol:14 participants were randomly assigned to the CBEX group and 8 were assigned to the placebo group.
The 1-repetition maximum (1RM) was determined for bilateral knee extensions before supplementation began. Also before the supplementation period, their hormone response to resistance training was determined (hormones listed below). Once before and once after the supplementation period, participants performed 5 sets of slow bilateral knee extensions (2 sec up and 2 sec down). Their first set was at 60% their 1RM and the load was increased 10% of their 1RM per set. Twelve ± 1 repetitions were performed per set and the same number or repetitions was performed after supplementation as before supplementation. To determine exercise-induced strength loss (fatigue index, %), a unilateral knee extension using an isokinetic dynamometer was utilized before and after exercise.
On test days, participants arrived at the laboratory after an overnight fast. A baseline blood sample was acquired and subsequent blood samples were acquired 0, 15, and 30 minutes after exercise. Blood was measured for epinephrine, norepinephrine, growth hormone, testosterone, cortisol, and lactate.
Summary of research findings:
- Epinephrine and norepinephrine responses were somewhat attenuated following supplementation in both the CBEX and placebo groups (no significant period x time interaction, however).
- Growth hormone levels were lowered after exercise following the supplementation period versus placebo (P = 0.07, period x time interaction).
- Free testosterone levels were slightly higher after CBEX supplementation versus placebo both before and after exercise.
- The post-exercise cortisol response was blunted more by the placebo than CBEX (P < 0.05, period x time interaction)
- Neither muscular strength nor resistance to fatigue changed in either group over the supplementation period.
Interpretation of findings/Key practice applications:
Ingestion of CBEX (including 1.2 g carnosine and 2.8 g anserine) for 30 days may affect how the body responds to resistance exercise. According to these results, CBEX may attenuate the growth hormone response to resistance training, however growth hormone is often desired by many resistance athletes who want to build muscle.
The authors also state that the CBEX attenuated epinephrine and norepinephrine after exercise perhaps because of the increased buffer capacity of the muscle cells due to higher carnosine concentrations. They did not measure carnosine concentrations, buffering capacity, blood pH, or any related parameter. They did not observe a difference in lactate production from exercise between the CBEX and placebo groups,. Also, the epinephrine and norepinephrine concentrations were attenuated in the placebo group, too, after supplementation. Overall, these data do not induce robust effects of the CBEX treatment on the hormonal response to exercise, although the trend toward greater reduction in growth hormone with CBEX versus placebo was interesting
This study was not designed to elucidate any mechanistic benefits of CBEX and the physiologic relevance of these biochemical changes, when present, to performance or body composition in athletes is not clear..
Moreover, this study was limited in that untrained subjects, who have lower intramuscular carnosine concentrations than athletes, were included and it may not be reasonable to translate their results into well-trained individuals. The training protocol was also performed fasted, in which case the hormone response will be much different than if a person is exercising in the fed state.