Essential Amino Acids During Training May Boost Muscle Recovery

We all know the dreaded feeling after leg day. When your spaghetti legs make it impossible to sit on the toilet without crying or cringing at the very least. Exercise can take a toll on muscles. When you do any sort of physical activity or exercise at an intensity or volume that your muscles were not previously used to, muscle fibers tear. It is literally damaging. This damage contributes to the soreness during the following days. One way to mitigate muscle damage and soreness is to eat sufficient dietary protein within the day and especially right after said workout. But what about having isolated EAAs (essential amino acids) in supplement form instead? And what if you had them during training rather than after training? Results from one study published January 2019 in the Journal of Physical Therapy Science appears to show some benefit.

The Study

Researchers from Japan, recruited ten untrained men for this randomized, double-blind, crossover study. Starting on day 0 and for the next 7 days, participants were randomized to ingest a 3.6 gram dose of a leucine-rich EAA mixture (LEAA) or carbohydrate-based placebo three times daily. The LEAA mixture was composed of 1.44g of leucine, 0.6g lysine, 0.4g valine, 0.39g isoleucine, 0.34g threonine. 0.24g phenylalanine, 0.12g methionine, 0.06g histidine and 0.03g tryptophan. Total daily dose amounted to 10.8 grams. The participants were instructed to flex their biceps at full power for 5 sets at 10 repetitions per set (day 1). Blood markers of muscle tissue damage were recorded prior to exercise and on days 1, 2, 3, 5 and 7 and changes were evaluated. Blood markers included creatine phosphokinase (CPK) and myoglobin concentration. After a 3 week washout period, participants repeated the bout of exercise and this time crossed over to use the alternate supplement (whichever one they didn't use the first round).

The Results

Researchers determined that CPK activity was increased in both groups after the bout of exercise, however, it was significantly reduced with the LEAA mixture compared to the placebo. There were however no significant differences between groups for myoglobin concentration or perceived (self-reported) muscle soreness.

Strengths and Weaknesses of the Study

  • Randomized - participants were randomly assigned to receive either LEAA or placebo; this helps with blinding
  • Double blind - neither participants or researchers knew which (supplement or placebo) they were consuming at any time, which gives the study strength because it eliminates bias
  • Placebo-controlled - this helps the researchers measure effectiveness of intervention compared to no intervention
  • CPK - increased levels of CPK in both groups showed that the exercise was challenging enough
  • Small sample size - not big enough to approximate population; low statistical power
  • Untrained men - untrained men have "easily damageable" muscles compared to a trained population
  • Diet unknown - we don't know what the rest of the participants' diet looked like; were there any other sources of protein consumed?


While the body of evidence to support EAA/BCAA supplementation is mixed--some studies show it is helpful and yet others show they are not anymore helpful than consuming regular protein--this study airs on the side that an LEAA supplement taken during training may help with recovery in untrained males. Not surprisingly, further research is warranted here. Leucine is the rock star of amino acids as it is essential to amplify the body's signal for MPS (muscle protein synthesis aka muscle building). So whether you are taking an isolated EAA supplement or eating whole dietary protein sources or protein powders (regardless of timing), you should make sure they contain enough leucine to trigger MPS which appears to help with recovery. Some research has indicated that about 2-3g of leucine is needed per meal to maximize MPS.

Leucine in Plant Proteins

Plant proteins provide varying amounts of leucine which can be used to trigger MPS. Growing Naturals Premium Rice Protein provides approximately 2.5g leucine per 30g of protein (2 small scoops). Uniquely, the leucine found in rice protein has been shown to absorb quicker into the bloodstream compared to leucine in whey protein. Pea protein provides the same at a 30g protein dose as well (2 small scoops). By: Scarlett Full, in-house Registered Dietitian

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