Updated: Nov 3, 2019
What Is HMB?
HMB, a powerful anti-catabolic supplement which has the potential to increase muscle mass and strength when used correctly!
HMB, β-hydroxy β-methylbutyrate, is a naturally occurring metabolite of Leucine, however because such low amounts of HMB is naturally produced, in order to create a pharmacologically active serum concentration you will need to supplement HMB through your dietary intake.
A healthy adult produces about 300mg (0.3g) of HMB per day, most supplemental dosages are between 1.5g and 6g per day.
HMB May Increase Protein Synthesis:
HMB has several mechanisms which have been identified in vivo, similar to its precursor L-Leucine, which cause the HMB-mediated increase in skeletal muscle mass, one of which is the increase in protein synthesis via phosphorylation of mTOR and subsequent activation of mTORC1.
HMB May Increase IGF-1 & GH:
HMB also appears to increase the serum concentration of Growth Hormone and IGF-1 via an unknown mechanism and also appears to amplify the secretion of Growth Hormone and IGF-1 in response to resistance exercise.
Increases in the Expression of IGF-1 mRNA may Contribute to the Increase in Muscle Protein Synthesis
HMB May Reduce Protein Breakdown:
HMB has also been found to reduce proteolysis, unlike L-Leucine, in a insulin-independent manner although it is still unknown how this occurs, protein breakdown is likely inhibited by HMB via inhibition of the 19S and 20S subunits of the ubiquitin-proteasome system and via inhibiting apoptosis of skeletal muscle nuclei, this mechanism of action is also unclear.
HMB May Improve Repair & Regeneration:
HMB appears to be metabolised into cholesterol and may be incorporated into skeletal muscle cell membranes improving its integrity and function, muscle damage markers (creatine kinase and lactate dehydrogenase) are also shown to be reduced possibly via this mechanism.
HMB May Have Other Hypertrophic Effects:
One other function of HMB is its ability to increase proliferation, differentiation and fusion of myosatellite cells which may increase skeletal muscle regenerative capacity, this happens due to ERK1, ERK2 and Akt phosphorylation.
HMB may also upregulate certain myogenic regulatory factors and gene transcription factors such as myoD, myogenin and MEF2.
Expression of MyoD and Differentiation‐Specific Markers MEF2 and Stimulation of Myogenic Cell Proliferation Via the MAPK/ERK and PI3K/Akt Pathways are also Other Potential Pathways of Muscle Growth.
HMB has been widely researched and proven to be an effective supplement to resistance training, possibly increasing strength and muscle mass considerably, and due to its anti-catabolic effects it has also shown to be useful in certain muscle wasting diseases such as cachexia.
There have been no reported side effects concerning HMB.