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

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HMB reduces muscle breakdown in endurance athletes

The leucine metabolite HMB, which is available in almost every supplement store and web shop, protects endurance athletes' muscles if they have to run distances of 20 km or more. Sports scientists from Iowa State University wrote about the phenomenon 12 years ago in the Journal of Applied Physiology.

Muscles make HMB from the amino acid leucine, and then convert HMB into HMG-CoA, one of the raw materials in cholesterol. Muscle cells use cholesterol for their membrane. They are unable to absorb cholesterol from the bloodstream, and thus have to rely on synthesising cholesterol themselves. The theory of the makers of HMB is that HMB supplementation speeds up intramuscular cholesterol synthesis, which means that muscle cells are capable of repairing their damaged membranes more quickly after physical exertion.

The HMB supplementation started 6 weeks before the test subjects did a 20-km run, and ended four days afterwards. The researchers measured the concentration of the enzymes lactate dehydrogenase [LDH] and creatine kinase [CPK] in the subjects' blood 4 weeks after supplementation [Pre], immediately after the 20-km run [Post] and 1, 2, 3 and 4 days after the run [1d Post, 2d Post, 3d Post and 4d Post]. The more enzymes there were in the blood, the greater the damage to the muscle cells.

HMB reduces muscle breakdown in endurance athletes

The researchers claim that the effects in the figures above are statistically significant. HMB decreases so muscle damage after the run and/or speeds up recovery, they conclude.

HMB is a controversial supplement. No one disputes that HMB has an anabolic effect, but whether this effect is so strong that athletes actually notice it is a matter of dispute among the experts. In addition, many of the studies that are positive about the effects of HMB come from scientists who are not entirely unbiased when it comes to promoting the substance. And this study is one of those.

Appl Physiol. 2000 Oct;89(4):1340-4.

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