HMB, a metabolite of leucine, has been shown to decrease muscle damage and have anti-catabolic effects that could translate into greater gains in lean body mass and muscular adaptations to resistance training. We recently tested the effects of a supplement containing 1.5 g HMB and a blend of amino acids on adaptations to12 weeks of heavy resistance training. The HMB-amino acid group had significantly greater increases in lean body mass (10 pounds more than control) and measures of muscle strength.  The form of HMB in that experiment was a calcium salt. Researchers at Iowa State have determined a free form of HMB may have greater bioavailability. They studied the effects of ingesting 0.8 grams of HMB in the typical calcium HMB form versus a new HMB free acid gel.  Plasma level of HMB peaked quickly (within 30 min) after the free acid gel form whereas the calcium form resulted in a gradual increase over a 2 hour period.  Over a 24 hour period, the free acid form of HMB showed a 15% greater area under the curve and clearance was similar as measured by urinary loss. Thus, the free acid form is more rapidly absorbed, and over a 24 hour period shows greater net clearance into tissues.
 . Kraemer WJ, Hatfield DL, Volek JS, Fragala MS, Vingren JL, Anderson JM, Spiering BA, Thomas GA, Ho JY, Quann EE, Izquierdo M, Häkkinen K, Maresh CM. Effects of Amino Acids Supplement on Physiological Adaptations to Resistance Training. Med Sci Sports Exerc. 2009 Apr 3. [Epub ahead of print]
  . Fuller JC Jr, Sharp RL, Angus HF, Baier SM, Rathmacher JA. Free acid gel form of β-hydroxy-β-methylbutyrate (HMB) improves HMB clearance from plasma in human subjects compared with the calcium HMB salt. Br J Nutr. 2011 Feb;105(3):367-72.