HMB for athletes: A brief review of the literature – Simone do Carmo

Athletes are always looking for that extra edge that will help them increase their strength levels, muscle mass, performance and recovery. Simone do Carmo investigates the effectiveness of the popular supplement HMB.

HMB (β-hydroxy-βmethylbutyrate) is a metabolite of leucine, a branched-chain amino acid. Although you can get HMB through leucine supplementation, the process is inefficient as only five per cent of the leucine is converted into HMB (1). HMB works in a similar way to leucine by activating the mTOR/P70S6K signalling pathway that stimulates muscle protein synthesis (1, 2). HMB also reduces muscle protein breakdown by inhibiting the key regulating component of the ubiquitin-proteasome proteolytic pathway, and it also seems to induce muscle cell proliferation via the MAPK/ERK and PI3K/Akt pathways (1, 3).

Therefore, the increase in muscle protein synthesis and decrease in muscle protein breakdown results in greater strength and lean body mass gains, as well as less muscle damage and faster post-exercise recovery. For this reason, HMB has been widely used as an ergogenic acid, especially among bodybuilders, and strength- and power-based athletes. At a molecular level, it looks like a promising supplement to take, but as I delve into the research, the findings are not so clear-cut. The effect of HMB supplementation on performance, body composition changes, and recovery has been researched in many populations, including untrained and trained, male and female, old and young. Since trained individuals are more likely to take supplements, my focus in this article will be on them.

Short-term intake for bodybuilders, strength- and power-based athletes

Ransone et al investigated the effect of HMB supplementation on muscular strength and body composition in 35 collegiate football players who averaged 20 hours per week of training under the supervision of qualified strength coaches (4). In a randomised, double-blinded and crossover trial, the participants were given either three grams of HMB per day (3g/day) for four weeks or a placebo, with a one-week washout period in between. No changes were found in muscular strength or body composition, perhaps indicating that HMB supplementation does not provide any benefits in trained individuals, at least in the short term.

A study by Kraemer et al investigated the effect of a supplement containing whey, HMB and a slow-release carbohydrate (isomaltulose) on recovery from highly demanding resistance exercise, compared to a whey protein supplement alone (5). In a double-blinded, counterbalanced and crossover trial, 13 individuals with at least one year of resistance training experience were given either the combined supplement or the whey protein supplement twice a day for two weeks and for two days after a 3-day intensive resistance exercise workout sequence, with a 2-week washout period. The participants were not allowed to engage in physical activity 24 hours and 48 hours after the 3-day workout sequence.

Muscle damage biomarkers, subjective ratings of muscle soreness, and countermovement jump performance were evaluated before, during, 24 hours and 48 hours after the 3-day workout sequence. Their dietary intake was also monitored to ensure they were maintaining an intake of one gram of protein per kilo body weight per day. The researchers did not evaluate any athletic performance or body composition markers, which would have been interesting. The results showed a significant benefit in taking the combined supplement, as suggested by the lower creatine kinase levels, interleukin-6 levels, subjective muscle soreness ratings and higher vertical jump power. However, the extent to which HMB impacted the latter results is unclear. It is difficult to isolate its effect because no group was supplemented with just HMB or HMB and whey.

Long-term intake for bodybuilders, strength- and power-based athletes

A longer-term and well-controlled study by Wilson et al looked at the effect of HMB-free acid (HMB-FA) supplementation (3g/day) on skeletal muscle hypertrophy, body composition, strength and power in resistance-trained athletes for 12 weeks (6). The researchers additionally wanted to determine the effects of HMB-FA on performance and muscle damage during an overreaching phase of the athletes’ training cycle.

Before I go further into this study, it should be noted that there are two available forms of HMB: calcium HMB (Ca-HMB) and free acid form HMB (HMB-FA). Most studies, including those by Ransone et al and Kraemer et al, use the calcium form. Although some believe the free acid form has superior bioavailability, which increases the absorption and retention of HMB, there is not enough evidence to support this claim (7).

Returning to the study, this was a three-phase (8-week periodised resistance training programme, followed by a 2-week overreaching phase and a 2-week taper) randomised, double-blind and placebo-controlled intervention. The researchers also controlled the participants’ diets to account for any possible dietary confounders. The participants’ muscle mass, strength and power were assessed at baseline and at weeks 4, 8 and 12, while cortisol, testosterone and creatine kinase levels were measured at weeks 9 and 10 of the overreaching phase. The HMB-FA supplementation resulted in a greater increase in total strength, measured as the combination of bench press, squat and deadlift, vertical jump power, gains in lean body mass and greater body fat loss than the placebo group after the 12 weeks of training.

During the overreaching phase, the HMB-FA supplementation prevented decreases in strength and power while also attenuating increases in creatine kinase and cortisol. Although the results clearly show that HMBFA makes a significant difference during the overreaching phase of the training cycle, the extent to which the superior lean body mass gains and increases in strength result from the attenuated creatine kinase and cortisol remains unclear. One must be careful not to jump to the conclusion that there is a causal relationship here. Nevertheless, this was a very well-controlled study and the fact that it was 12 weeks in duration provided enough time to see measurable results in trained athletes, unlike the short-term study by Ransone et al.

In another similarly randomised, double-blind and placebo-controlled study, researchers investigated the effects of HMB-Ca supplementation (37.5 mg/kg body mass per day) for 12 weeks on athletic performance, body composition and inflammatory markers in elite canoeists (8). During the 12 weeks, all the athletes participated in a resistance training programme while also doing sprint-specific training and technical training with the boat. The results showed that, as a result of their strength parameters developing faster, the HMB-Ca group had a better athletic performance response.

These parameters were measured as the distribution of units in the force-time curve during a standardised test: the medium force, peak force, rate of force development, impulse and fatigue index. The results also showed that a dose of 37.5 mg/kg body mass per day of HMB-Ca could potentiate an increase in lean body mass, which would correspond to the increases in strength associated with resistance training in elite athletes. The researchers point out that the physiological mechanism behind this is still unknown but suggest that supplementing with HMB-Ca might attenuate skeletal muscle damage when these muscles are stressed. Serum creatinine was significantly higher in the supplemented group. There was also a reduction in lactate dehydrogenase in both groups, with a more pronounced reduction in the HMB-Ca group. Total creatine kinase increased in the placebo group and decreased in the HMB-Ca group, but neither change was significant.

However, the HMB-Ca group presented a progressive decline in skeletal muscle creatine kinase activity over the months of the study, suggesting that HMB-Ca may have a protective anti-catabolic effect. This explanation is very similar to the study by Wilson et al, which showed the benefits of HMB-FA during an overreaching phase as reducing exercise-induced muscle damage and thus accelerating the super-compensation response. The present study (8) also shows that even though HMA-FA is thought to have superior bioavailability, the HMB-Ca form is also a beneficial supplement.

A study by Lowry et al investigated the effect of supplemental HMB-FA (3g/day) with ATP (440mg/day) in resistance-trained individuals for 12 weeks on the premise that ATP would help maintain performance under fatigue and HMB-FA would speed up recovery (9). This was a double-blind, placebo-controlled, three-phase study, similar to Wilson et al’s training protocol. The participants’ dietary intake was also controlled. The HMB-FA and ATP supplement showed impressive gains in lean body mass, strength, vertical jump, and Wingate power. The results were so impressive for trained athletes that they have led to some recently published criticism by Philips et al (10). It would be interesting to see whether this study’s results could be replicated.

HMB for endurance performance

HMB is generally perceived as an ergogenic supplement for bodybuilding and strength- and power-based sports. However, a unique study investigated the effect of HMB on aerobic capacity as the main outcome in 58 well-trained athletes (11). The researchers also looked at body composition changes, intramuscular enzyme activity, anabolic and catabolic enzymes, as well as lactate concentrations at baseline and after the 12-week supplementation period. The participants were given 12 weeks of HMB-Ca supplementation (3g/day) or a placebo in a randomised, double-blinded and crossover manner, with a 10-day washout period. The participants’ dietary intake was monitored by completing dietary records every two weeks.

After the 12 weeks of HMB-Ca supplementation, the participants’ maximal oxygen uptake, the time to reach the ventilatory threshold, and the threshold heart rate at the ventilatory threshold had increased significantly. In addition, the HMB-Ca supplementation led to significant improvements in body composition, with an increase in lean body mass and a concomitant decrease in fat mass. Although no differences in lactate, lactate dehydrogenase and creatine kinase were recorded at the end of the 12-week period, an increase in testosterone was observed in the HMB-Ca group, while cortisol increased in both groups.

One might speculate that the increase in testosterone, an anabolic hormone, explains the body composition changes. However, when looking at the testosterone-to-cortisol ratio, there was no difference between the groups, which makes testosterone less likely to have played a significant role. This study shows that HMB is not just a ‘strength’ supplement; it can also benefit endurance performance by increasing an athlete’s aerobic capacity and the intensity of exercise above which their breathing becomes too difficult.

HMB during periods of caloric restriction

As HMB has been shown to have anti-catabolic effects in patients with sarcopenia and cachexia (12), it would make sense for it to also be effective at preserving muscle mass during periods of caloric restriction, particularly in weight-making athletes. Unfortunately, the research on this is scarce; to my knowledge, there is only one preliminary study (13). This study looked at eight elite female judo athletes and found that 3g/day of HMB-Ca for three days during severe caloric restriction revealed a trend for preserving lean body mass and significantly decreasing body fat percentage. The small sample size, plus the fact that the study lasted only for three days, makes it difficult to draw any conclusions and more evidence is clearly needed.

Conclusion

The evidence suggests that HMB is most effective at improving strength parameters and endurance capacity measures when taken in the long term (at least 12 weeks) in trained individuals during periods of intense training. This was also recently concluded in a review (14). That said, HMB does not have the same standing as whey protein or creatine, which are commonly taken for strength and muscle gains, and I believe more evidence from well-controlled studies is needed to draw clearer conclusions. Since the research so far points in a beneficial direction for HMB intake, and it is considered a safe supplement for long-term use in all ages (15), I think it is worth giving HMB a try to see if it works.

The International Society of Sports Nutrition’s position suggests that a dose of 38mg/kg body weight or 1-3g should be ingested 60-120 minutes before exercise if consuming HMB-Ca, or 3060 minutes before exercise if consuming HMBFA. To optimise the chronic effect of HMB, it is recommended that 3g be consumed daily, divided into three equal servings, for at least two weeks shortly before an intense bout of exercise or training phase (7).