HMB has recently become a popular dietary supplement used to promote exercise performance and skeletal muscle hypertrophy by many exercise enthusiasts. A lot of previous studies have found that HMB supplement is beneficial to reduce muscle damage and decrease protein catabolism, which leads to increased gains in muscle size and strength when associated with resistance exercise. However, it is very important to note that these studies have focused primarily on the effect of calcium-HMB (the conventional form of the supplement). A recent study have indicated that HMB consumed in free acid gel form produced earlier and greater peaks in plasma HMB and improved clearance of HMB from plasma compared with an equivalent dosage of calcium-HMB by examining whether HMB in free acid gel form will improve HMB availability to human tissues. This finding suggests greater bioavailability of HMB when ingested as a free acid in gel form. Therefore, the aim of the present study was to investigate the efficacy of a newly developed form of HMB (consumed as a gel form) in reducing indicators of muscle damage after a single bout eccentric resistance exercise.

Seventeen male and sixteen female volunteers were randomly assigned into 5 treatment groups by matching based on average peak force on dominant leg. The 5 treatment groups consisted of Placebo (one capsule placebo and one 3ml-syringe gel placebo); Pre-exercise Ca-HMB (1capsule containing 1 g calcium-HMB ingested 30 min prior to strength test); Pre-exercise Gel-HMB (3 mL free-acid gel containing 1 g HMB ingested 30 min prior to strength test); Pre + Post Ca-HMB (1 capsule containing 1 g calcium-HMB 30 min prior to strength test plus 3 daily doses for 4 days); Pre + Post Gel-HMB (3 ml free-acid gel containing 1 g HMB 30 min prior to strength test plus 3 daily doses for 4 days). In a double-blind design, all subjects completed eccentric exercise bout which aimed to induce delayed onset (24-96 hr later) muscle soreness. During the experimental period, the blood draw and following tests were repeated at 24 hr, 48 hr, 72 hr and 96 hr after performing the eccentric exercise protocol: soreness feelings scale, vital signs (blood pressure and heart rate), height, body mass, thigh circumference (both Legs) and isometric leg extension strength.

There was a reduction in isometric leg extension strength and an increase in muscle soreness, thigh circumference and serum indices of damage (CK and LDH) following eccentric exercise. However, no significant differences were observed in changes of muscle soreness, maximal isometric leg extension strength, serum CK, LDH and thigh circumference between any treatment contrast from immediately to 48 h and 48h to 96h after eccentric exercise.

Our findings suggest that there were no clear effects of HMB in free acid gel on indirect markers of muscle damage than either a placebo or calcium-HMB treatment following a single bout of eccentric exercise.