|Image 1: This is where HMB could actually make a difference, the two more reps, the one more sprint, which after weeks and months of training can decide over victory or defeat.|
HMB works, we just don't know exactly how and for whom
As Dr. Connelly pointed out on the last BodyRX Show (highly recommended, especially for Layne's intellectual exchange with Dr. Jeff Volek), it stands out of question that HMB works. There are in fact more than a dozen of studies which show that supplementation with adequate amounts of this leucine metabolite has anti-catabolic effects in various conditions of skeletal muscle atrophy (Nissen. 2003; Smith. 2005). What is still debatable, though is whether and to which extent athletes, in general, and bodybuilders, in particular can benefit from these effects. In view of the increasing awareness of the importance of leucine, the metabolic precursor of b-hydroxy-b-methylbutyrate (HMB), most athletes in this subgroup probably consume somwhere between 20-30g of leucine from the 300g of protein they are feeding themselves in the form of protein shakes and lean meats alone (with reference to the data that is presented in figure 1 it is noteworthy that the comparison Nissen made is not "fair", because the many of the HMB studies were conducted with "sick" people, while the majority of studies on protein supplements used either healthy people or athletes). With an average conversion rate of ~5% (of dietary leucine), we would have to estimate their daily HMB "production" to roughly 1.0-1.5g, which is interestingly at the lower range of what has been shown to ameliorate muscle wasting in cancer cachexia studies (Eley. 2007; Kovarik. 2010).
|Figure 1: Calculated effect sizes of creatine, HMB, chromium, androstendione, DHEA and protein supplements on strength and lean mass gains (adapted from meta-review by Nissen et al.; Nissen. 2003)|
|Figure 2: Changes (vs. placebo) in ATP and glycogen content, as well as citrate synthesis in red and white portion of rat gastrocnemius muscle after 4 week supplementation with 320mg/kg HMB (data adapted from Pinheiro. 2011)|
|Figure 3: Tetanic force production (normalized to muscle weight) in rats receiving 320mg/kg HMB or placebo for 4-weeks; successive tetanic contractions were evoked at 100 Hz each 10 s of interval (data adapted from Pinheiro. 2011)|
Fine!? Now, tell me: Is HMB worth it?
In view of the fact that neither the muscle size (cross-sectional area) nor the lean mass of the rodents in the HMB group differed from their placebo supplemented peers (btw. the animals were not "trained" in the course of the 4-week study), we must conclude that the effects of HMB, similar to those of creatine, are not what you would call "immediately anabolic". In a real world training scenario the metabolic advantage (increased ATP stores, increased glycogen stores and increased oxidative capacity) the rats in the HMB group gained over the 4-week study period, would allow trainees to do those 1-2 reps more which in weeks and months would then translate into this one additional pound of muscle or the 10th of a second that can make the difference between victory or defeat - whether those 1-2 reps are worth the roughly 64$ it would cost to copy the supplementation regimen used in the study (320mg/kg in rats would equate to 53mg/kg per day for humans), does yet depend on who you are, what you want to achieve and how much money you have to spend... and if you do not have your regular diet and training in check, don't even think of HMB (let alone one of those "test boosters" ;-)