5% Strength: STAT inhibitor PL=0-6.7 % vs. HMB +15.7 % – 23.5 % Ransone 2003 College football players Progressive resistance and endurance exercise No No 4 weeks, 3 grams per day HMB-Ca No Skin Folds Bench Press, Power Cleans, Squats 1-RM FFM: +0.3 FM: – 3.8 Strength: 1.7 % increase Kreider 2000  Trained, college football players Offseason strength and conditioning program Yes No 4 weeks, 3 grams per day HMB-Ca No DXA Bench Press, Power Cleans, Squats 1-RM, 12×6 second sprint performance No Effects O’Connor 2007 Trained rugby players, 25 yrs of age Progressive resistance training No No 6 weeks, 3 grams of HMB-Ca or HMB-Ca + Creatine per day 3 grams creatine
per day Skin Folds Squat, Bench Press, and Deadlift 1-RM Wingate Power Neither HMB-Ca nor creatine had an effect Slater 2001 College-aged, trained polo players and rowers Non-controlled workouts assigned by the athletes’ respective coaches Unknown No 6 weeks, 3 grams per day HMB-Ca No DA Bench Press, Hip Sled, Pullups 3-RM No significant effects * Abbreviations used in the table. TOBEC-total-body electrical conductivity; DXA-Dual-energy x-ray AZD8186 price absorptiometry; BIA-bioelectrical impedance; FFM-fat free mass; FM-fat mass; LBM-lean body mass (TOBEC). HMB metabolism, pharmacokinetics and retention Metabolism HMB is naturally produced
in animals and humans from the amino acid leucine . The first step in production of HMB is the reversible transamination of leucine to α-keto-isocaproate (KIC) by the enzyme branched chain amino acid transferase  (Figure 1). After leucine is metabolized to KIC, KIC is either metabolized into isovaleryl-CoA by the enzymeα-ketoacid dehydrogenase in the mitochondria, or into HMB in the cytosol,
by the enzymeα-ketoisocaproate dioxygenase . KIC is primarily metabolized into isovaleryl-CoA, with only approximately 5% of leucine being converted into HMB . To put this into perspective, an individual would need to consume over 600 g of high quality RSL3 mw protein to obtain the amount of leucine (60 grams) necessary to produce the typical 3 g daily dosage of HMB used in human studies . Since consumption of this amount of protein is impractical, HMB is typically increased via dietary supplementation. Figure 1 The metabolism of beta-hyroxy-beta-methyl-butyrate. Rate of appearance and retention between varying forms of HMB As a dietary supplement, HMB has been commercially available mafosfamide as a mono-hydrated calcium salt, with the empirical formula Ca (HMB)2-H2O (HMB-Ca). The magnitude and rate of appearance of HMB following ingestion is dependent on the dose, and whether or not it is consumed with additional nutrients. Specifically, Vukovich et al.  found that 1 g of HMB-Ca resulted in a peak HMB level in blood two hours following ingestion, while 3 g resulted in peak HMB levels 60 minutes after ingestion at 300% greater plasma concentrations (487 vs. 120 nmol·ml-1), and greater losses in urine (28% vs. 14%), for 3 and 1 g HMB-Ca ingestion, respectively.