Journal Title (Medline/Pubmed accepted abbreviation): Appl. Physiol. Nutr. Metab.
Page numbers: 242-253
doi (if applicable): 10.1139/H10-104
Summary of Background and Research Design
Background: Dietary protein is in higher demand after intensive exercise for use in energy utilization, muscle repair, and adaptation of body structure to that exercise. The amino acid leucine, specifically, has been identified as a key signaling molecule in protein synthesis.
Hypothesis: A high leucine, high protein beverage with carbohydrate, when ingested with a high carbohydrate food after 3 days of intense cycling training, will improve performance in a subsequent cycling session.
Subjects: Ten well-trained male cyclists and triathletes, age 33 ± 9 yrs. old
Experimental design: randomized, double-blind, placebo-controlled, crossover design
Treatments: As a recovery beverage, cyclists consumed a high-leucine, high-protein beverage (0.2/0.4/1.2/0.2 g per kg body weight per hr of leucine/total protein/carbohydrate/fat, respectively) or an isocaloric control beverage (0.06/1.6/0.2 g per kg per hr of protein/carbohydrate/fat). Overall diet during the training protocol was clamped at 1.6 g/kg/day.
Protocol: The subjects underwent two 9-day blocks of an exercise and diet protocol. The first 3 days of the block (days -8, -7, -6) consisted of standardized lead-in training. Day -5 was a rest day. The subjects then performed 3 consecutive days of high-intensity cycling (days -4, -3, and -2) after which they consumed the treatment recovery beverage in the post-exercise period, had 1 rest day, and then completed the performance test the next day (day 0). The performance test consisted of ten maximal power sprints (1.5-3 min) with 5.43 min to rest in between. Performance during this test was used to assess the recovery of the subjects after the 3 days of training + the treatment beverage.
After at least 2 wks, the subjects repeated the same protocol, only with the other treatment. Participants reported muscle soreness before each training session and the performance test. Urine samples (24 hr) were collected from day -4 to day 0 to analyze nitrogen excretion (marker of protein breakdown). Sweat was acquired in days -3 and -2 for analysis of nitrogen content and a blood sample was acquired before and after the training session on day -4 to assess markers of muscle damage plasma amino acid concentrations. Additional samples were acquired on days -3, -2, and 0 for assessment of muscle damage.
Summary of research findings
- Plasma leucine, essential amino acids, and total amino acid concentrations were greater after exercise when the high leucine beverage was consumed.
- The average sprint power of the cyclists during the performance test was 325 W for the leucine beverage and 320 W for the control beverage. A simple calculation of the difference between these numbers (325-320/320) shows the increase to be 1.6% for the treatment vs. control, but the authors stated a difference of 2.5% and that this increase was significant (p=0.013) with a 93.3% chance of benefit to the athlete. It is not clear from the study methods exactly how the performance difference of 2.5% was calculated.
- The leucine beverage decreased perceived overall fatigue by 13% (90% CL ± 9.2%), but effects on leg fatigue or soreness were trivial.
- Nitrogen balance was slightly negative for both treatments, indicating that there is higher nitrogen loss than nitrogen intake
- There was a small reduction in creatine kinase levels after the leucine treatment compared to the control, suggesting that there was less muscle damage. There were no clear effects, however, on blood lactatate dehydrogenase levels, another potential marker of muscle damage.
Interpretation of findings/Key practice applications
A high-leucine, high-protein recovery beverage, when consumed after training in conjunction with high-carbohydrate food, increased performance slightly in a later cycling trial versus isocaloric carbohydrate in the postexercise recovery period. This may be due to more rapid muscle repair.
The diet that the cyclers followed, considering their intense training protocol, made them slightly protein deficient by nitrogen balance testing. This is true for both treatments, however, but still might suggest that these findings only apply to cyclists that are slightly protein deficient. In addition, the two recovery diets differed in both free leucine and protein, so it is not clear which of these factors was the most influential. Finally, the authors report an intake of free leucine of 17.6 g from the leucine-protein supplement, which is a large amount of free leucine relative to the amounts available in many commercial supplements. Thus, it is not clear how these findings might benefit athletes taking lower levels of free leucine.