It’s been circulating through the bodybuilding world for years, but HMB, a metabolite of the amino acid leucine, is just starting to break into the endurance community. The reason: Some studies point to astonishing results—like a 55 percent increase in bench press performance among experienced athletes.
Benching your body weight doesn’t matter on the bike, but HMB allows you to “gain muscle mass more quickly and lose body weight without compromising muscle tissue,” Sims says. The supplement prevents protein breakdown, making it particularly useful for older athletes or people doing lots of endurance training where recovery becomes an issue, Dr. Joyner says.
Exactly how big a boost can cyclists expect? A recent study on eight riders with an average training volume of 300 miles per week showed supplementing with HMB increased the time it took them to reach their VO2 peak—a very high level of energy output—by eight percent.
Most studies recommend taking three grams of HMB daily for maximal benefit. Upping the dosage may not have an effect—a recent study found that taking six grams had no practical benefit on strength gains over the three-gram dose.