Exercise strengthens muscles by naturally destroying the protein of muscle cells. This causes the body to rebuild even more protein (protein synthesis). This in turn results in bigger muscles and greater muscle strength.
What is HMB?
HMB (beta-hydroxy-beta-methylbutyrate) is a metabolite formed when the amino acid leucine is broken down in the body. Amino acids are the building blocks of protein. Proteins are the building blocks of muscle. The body has to undergo protein synthesis in order to build muscle. The HMB supplement increases protein synthesis and decreases protein breakdown in muscle.
One of the first and best studies on HMB supplementation and resistance training was conducted by researchers in 1996. The study participants consisted of 41 healthy young men divided into two groups. Both groups ate a normal but nutrient controlled diet for the duration of the study. One group also took a protein supplement containing 3 times the recommended daily allowance for protein.
The researchers then divided each of these 2 groups into 3 subgroups. Each group had different levels of daily HMB supplementation: 0 grams (a placebo), 1.5 grams, or 3 grams. At the start of the study, the researchers measured the men’s muscle strength and body composition (percentage of muscle and fat). To calculate breakdown of muscle protein the researchers also took weekly measurements of three biochemicals that show up in the blood or urine when muscle is being broken down by exercise: plasma creatine phosphokinase, lactate dehydrogenase, and urinary 3-methylhisti-dine, respectively. The study lasted 3 weeks. In that time, the men lifted weights 3 times a week, using a combination of free weights and weight machines. They performed 14 resistance exercises for the lower and upper body.
The HMB supplementation group had significant results. The men getting 1.5 grams of HMB had twice the muscle gain of those getting the placebo. The individuals getting 3 grams had 3 times the muscle gain. All the participants were lifting weights and they all got stronger. The placebo group got 8 % stronger. The 1.5 gram HMB group got 13 % stronger. The 3 gram HMB group got 18 % stronger. When they started resistance training, the men getting the placebo went from 3 % of muscle broken down per day to 6 %. The 1.5 gram HMB supplement group increased from 3 to 5.5 %. The 3.0 gram HMB supplement group increased from 3 to 4.5 %. This means that the more HMB supplement they were taking, the more their muscles were protected. The extra protein didn’t help with muscle gain, muscle strength, or prevent muscle breakdown.
Several other studies on HMB supplementation and weightlifting have since shown equally positive results. There’s a good possibility that HMB supplementation can result in improved muscle strength, with less muscle loss from the stress of exercise. An HMB supplement has no effect on body composition without resistance training.
When supplementing with HMB, current evidence suggests 1 g of HMB taken 3 times per day, for a total of 3 g of HMB daily (or 38 mg/kg of bodyweight).