Journal Title (Medline/Pubmed accepted abbreviation):Br. J. Nutr.
First Page: 538-544
Background: β-Hydroxy-β-methylbutyrate (HMB) is a dietary supplement that has been associated with increases in muscle size, strength, and power as well as quickened recovery. It is found in the body normally as a metabolite of the amino acid leucine.
There are several different forms of HMB. HMB can be a free acid (HMB-H+) or as a calcium salt (HMB-Ca2+). The free acid form reaches the circulatory system faster than the calcium salt.
Hypothesis: The free acid form of HMB will reduce markers of muscle damage, inflammation, and muscle protein breakdown compared to a placebo. In addition, the free acid of HMB will quicken recovery and promote an enhanced anabolic environment in regard to circulating hormones.
Experimental Design: randomized, placebo-controlled
Subjects: males regularly involved in resistance training, age 21.6 ± 0.5 y, n = 20 participants
Treatments: A sweetened, orange flavored beverage either included HMB (3 g/day) or not. The beverage was divided into 3 equal servings and was consumed before exercise, at lunch, and at dinner on a single day.
Protocol: Participants were first evaluated for one repetition maxima (1RM) for full squat, bench press, and dead lift as well as body composition using dual x-ray absorptiometry (DEXA). Total body strength was calculated as the sum of the three 1RMs. The participants then reported to the laboratory after an overnight fast. A baseline blood draw was acquired, and the supplement was consumed 30 min before commencing the exercise training. The exercise protocol consisted of 3 sets of 9 resistance exercises with 1 min in between sets. The weight lifted was adjusted so that the participants lifted about 12 repetitions per set. A second blood sample was acquired 48 hrs after the resistance training bout. Blood samples were assessed for creatine kinase (a marker of muscle damage), testosterone, cortisol, and C-reactive protein (a marker of inflammation). Twenty-four hour urine samples were collected the day before training and 48-72 hrs after training and analyzed for volume, 3-methylhistidine (3-MH; marker of muscle protein breakdown), and creatinine (indicator of muscle breakdown). “Perceived recovery status” (PRS) was assessed with a subjective score from 0-10 with 0 being the least bit recovered and 10 being completely recovered. PRS was reported before and 48 hrs after the workout.
- There were no differences in age, height, body weight, or strength between participants. In addition, there were no differences in the training volume between groups at the exercise session.
- Training led to significant increases in serum creatine kinase, though the increase was attenuated with HMB (from about 150 IU/L to start to 322 ± 35 IU/L in the HMB group and about 604 ± 83 IU/L in the placebo group).
- The PRS score decreased from 9.1 ± 0.4 to 4.6 ± 0.5 in the placebo group and from 9.1 ± 0.3 to 6.3 ± 0.3 in the HMB group (p = 0.005), indicating that those who took HMB perceived that they had recovered better from the workout.
- The urinary 3-MH:creatinine ratio reports the amount of muscle protein breakdown. There was a trend for less muscle protein breakdown in the HMB group compared to the placebo group (p = 0.08).
- There were no differences between groups in regard to changes in plasma total or free testosterone, cortisol, or C-reactive protein.
Key practice applications: Supplementation with 3 g of free acid form of HMB, divided over the course of the day, quickened recovery from an intense resistance training workout and decreased muscle damage. This study is important because it shows that HMB can be effective the first day it is consumed, and doesn’t need to be consumed for several weeks before effects are observed.