Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Leucine retains muscle mass when you're not training

Taking a supplement of the amino acid L-leucine inhibits the breakdown of muscle mass in muscles that are not active. Researchers at the University of Sao Paulo in Brazil discovered this when they did an experiment with rats.

Leucine has an anabolic effect on muscle cells. This is probably because the muscle cells invest more energy in synthesising muscle protein the more leucine metabolites they 'see'. The researchers wanted to know whether leucine can be used to counteract the catabolic mechanisms that start up when muscles become inactive and which lead to accelerated muscle tissue breakdown.

The researchers gave rats a single daily dose of 2.7 g leucine per kg bodyweight, introducing it through a tube. A control group received no leucine. Three days after supplementation started, the researchers put one of the hind legs of each rat in a splint. The splint was kept on for seven days, preventing the animals from using the muscles in that leg. During the entire period the rats in the experimental group were given leucine, and after seven days the splint was removed.

The mass of the soleus muscle decreased less in the animals that had received leucine supplementation. And when these animals regained the use of their hind leg, they also regained muscle mass more quickly.

Leucine retains muscle mass when you're not training

During the period of enforced inactivity, the catabolic genes MAFbx and MuRF1 became more active. When these genes are active, the muscle cell starts to break down its protein structures. But the leucine supplementation inhibited the genes' work.

Leucine retains muscle mass when you're not training

Leucine retains muscle mass when you're not training
Leucine supplementation also reduced the effect of ubiquitine, as shown here. Think of ubiquitine as a kind of marker flag. If the muscle cell attaches ubiquitine to a protein, then that protein is on the list for being chopped up by a molecular 'shredder'. The official name of the shredder is proteasome.

The figure below shows that the leucine supplement had no effect on the production of muscle protein. So in inactive muscles leucine is exclusively anticatabolic, and not anabolic.

Leucine retains muscle mass when you're not training
If you convert the dose used into human proportions, you'd arrive at 0.18 to 0.27 g per kg bodyweight per day. Human studies have shown that leucine only appears to work in doses of 5 g or more, and in combination with protein-rich food.

Another recent study has shown that a daily dose of 20 g creatine protects inactive muscles from withering away. We wonder what would happen if you combine creatine with leucine?

Muscle Nerve. 2010 Jun; 41(6): 800-8.

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