The effects of adding leucine to pre and postexercise carbohydrate beverages on acute muscle recovery from resistance training 
Journal Title (Medline/Pubmed accepted abbreviation):  J Strength Cond Res                
Year:  2010
Volume: 24
Number: 8
Page numbers: 2211-2219
doi (if applicable): 

Summary of Background and Research Design

Hypothesis:Leucine’s ability to augment muscle protein synthesis would lead to a reduction in damage to myofibrillar and cytoskeleton proteins, thereby preventing an increase in serum creatine kinase (CK) and lactate dehydrogenase (LDL) in a subject consuming a leucine-carbohydrate beverage. It was further hypothesized that the reduced muscle protein damage would result in decreased muscle soreness after exercise.

Subjects:A total of 20 subjects were recruited for the study (mean age 22.9 y, mean body weight = 82.7 kg, for men and 67.4 kg for women). All were healthy with at least 1 year of resistance training experience. All subjects did the squat exercise as part of their normal exercise routine. Subjects were randomized into either a treatment group (8 males, 2 females) or placebo group (9 males, 1 female)

Experimental design:Independent groups, between subjects design, randomized, double-blinded

Control: 0.25 g carbohydrate/kg body weight in 16 oz. water provided 30 min before and immediately after exercise (0.5 g carbohydrate/kg total). 
Treatment: Control solution plus 22.5 mg leucine per kg, provided 30 min before and immediately after exercise (0.5 g/kg carbohydrate and 45 mg leucine/kg total).  For an average subject, this amounts to about 20 g carbohydrate and 1.8 g leucine given both before and after exercise (40 g carbohydrate and 3.6 g leucine total)
Protocol: Following a pretesting visit to determine 1 repetition maximum on the squat exercise, subjects made another visit to the lab and had baseline blood measurements taken. The first drink was provided and, after a 30-min wait, the subjects underwent an exercise protocol consisting of 6 sets of squats at 75% of the 1-rep max. Additional blood samples were obtained from the subjects at 24, 48, and 72 h postexercise and were analyzed for creatine kinase and lactate dehydrogenase to assess levels of muscle damage. Delayed onset muscle soreness (DOMS) was assessed using a 7-point Likert type scale at the same time points as the blood draws. Subjects kept dietary records during the recovery period. At the 72-h postexercise visit, the subjects performed another 6 sets of squats to determine the degree to which a performance decrement might persist with each drink.

Summary of research findings:
  •   A pilot study with 6 subjects prior to the main study demonstrated that the squat exercises significantly increased CK, LDH, and DOMS (data not shown)
  • The addition of leucine to the carbohydrate solution did not decrease CK, LDH, or DOMS.
  • Both groups experienced some decline in squat performance in the second squat session, but there were no differences between the two groups
  • There was an inverse correlation (R @ -0.36, P = 0.004)) between dietary leucine intake (supplement not included) and serum creatine kinase level at the 24-h postexercise measurement. The correlation coefficient for protein, however, was non-significant. Dietary intakes of protein, carbohydrate and branched chain amino acids were not significantly different during the first, second, or third 24 h of the recovery period.

Interpretation of findings/Key practice applications:

In this study, addition of just leucine to a carbohydrate beverage did not improve DOMS or biochemical markers of muscle damage. The authors speculated that perhaps the addition of whole protein or larger doses of leucine might be required to observe an improvement in these parameters. Also, given that these subjects were already resistance trained (i.e., more fully adapted to exercise) and that the exercise was quite intense, it is possible that the degree of muscle damage that the subjects were able to induce would overwhelm any effect of additional leucine.
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