Dietary Supplement myHMB Gluten Free Helps Improve Muscle Strength and Body Composition Provides Support Against Muscle Protein Breakdown Hmb is among the most researched of nutritional supplements – with studies focusing on men and women, young and old, athlete and non-athlete. Hmb is a key metabolite of the essential Branched Chain Amino Acid (Bcaa) L-Leucine – the most important amino acid for building and retaining muscle. Regular, consistent supplementation with Hmb has been clinically shown to support significant increases in muscle mass and strength, when combined with resistance training.