They categorize it as a legal substance that does not infringe on existing doping laws, and say it appears to have no harmful effects. Juhn is a family and sports medicine doctor at the University of Washington in Seattle. And many experts, including Juhn, are skeptical of its effectiveness. It definitely does not have very convincing data. Juhn explains that HMB is a substance formed naturally when the body breaks down the amino acid leucine.
Amino acids are the building blocks of protein, and proteins are the building blocks of muscle.
This theory is problematic, though, because building new muscle requires some breakdown of protein within the muscle tissue, he says. From what the authors found, they suggest that HMB seems to work primarily in the untrained athlete during resistance training . The authors of the review, Gary J. Slater and David Jenkins, hail from the Australian Institute of Sport in Canberra and the University of Queensland in Brisbane, respectively. Lean tissue also seemed to increase, in the same dose-response manner. But Juhn points out that this particular study was funded by Metabolic Technologies, a maker of HMB supplements.