Sport scientists and coaches design an athlete's diet to meet energy and nutrient requirements to ensure that optimal training can be maintained, and competitive performance can be maximized. There is a common belief that, in conjunction with a well-designed training program and diet, the appropriate ingestion of additional dietary supplements can further enhance training and exercise performance. One such supplement that has attracted recent interest is β-alanine. This growing interest stems from recent research that has identified β-alanine as the rate-limiting precursor to carnosine (β-alanyl-L-histidine) (42,44) which, among other roles, is thought to be an important physiological buffer because it can readily accept protons during contraction-induced acidosis (11). Carnosine is found naturally in meat products, particularly deep water species of fish, but supplementation with β-alanine seems to be necessary to achieve the active daily dose required to significantly elevate intramuscular carnosine (56). Skeletal muscle is unable to synthesize the 2 carnosine precursors, L-histidine, and β-alanine, so the concentration of intracellular carnosine is largely dependent on the uptake of these amino acids from the bloodstream (1). The affinity of carnosine synthetase for L-histidine is greater than β-alanine, in addition to the fact that L-histidine is in greater concentrations in plasma than β-alanine, and as a consequence, it is considered that β-alanine is the rate-limiting precursor of skeletal muscle carnosine concentration (42,44).
It has been well established that chronic β-alanine supplementation (1.6–6.4 g·d−1 for a period of 2–10 weeks (4,26,44,95)) can significantly increase muscle carnosine concentration. Augmented muscle carnosine concentration may improve athletic performance in exercise tasks that accrue a high level of muscle acidosis. In support of this affirmation, a number of studies have evaluated the potential ergogenic effects of β-alanine supplementation on a variety of sport-specific performance protocols in the athletic population and have met with varying results. Studies have reported ergogenic benefits after β-alanine supplementation in punching efficiency in amateur boxers (27), small but potentially worthwhile improvements in average power output in a 4-minute cycling time trial (12,54) and worthwhile improvements in 100- and 200-m swimming performance (23). In contrast, β-alanine supplementation has been reported to provide no benefit to 400-m running performance in trained sprinters (26) and failed to improve endurance cycling performance in well-trained cyclists (20). These equivocal findings may be because of the individual variability in carnosine loading, the training status of the participants, or the type of performance protocol that was employed.
Several excellent reviews regarding the ergogenicity of β-alanine supplementation have been published (1,19,25,78,80,112). These reviews generally concluded that β-alanine supplementation serves to increase muscle carnosine content. In addition, β-alanine supplementation may provide an ergogenic benefit to performance during short-duration high-intensity exercise. However, coverage of its effects on athletic performance was limited because few studies were available. Questions were also raised whether results observed in laboratory settings would transfer to sport-specific measures of performance, and whether supplementation could enhance intermittent and repeated bouts of maximal exercise. Furthermore, a recent avenue of research has investigated whether the cosupplementation of β-alanine and sodium bicarbonate can provide an additional ergogenic benefit beyond what is possible with either supplement alone. A considerable number of studies have been published subsequently meriting a modernization. The aim of this review was to update, summarize, and critically evaluate the findings associated with β-alanine supplementation and exercise performance with the most recent research available and provide athletes and coaches with an insight into the practical implications for the most effective of β-alanine loading strategies and the different types of competitive performance that may benefit most from augmented muscle carnosine. For this purpose, a computer search for relevant peer-reviewed articles (excluding abstracts and unpublished theses and dissertations) was performed in May 2013 by entering various combinations of the following key words into PubMed, SPORTDiscus, MEDLINE, and Scopus; “β-alanine,” “ergogenic aids,” “supplementation,” “exercise performance,” “sport,” and “carnosine.” A manual cross-reference of relevant articles was also performed.
Optimizing β-Alanine Supplementation Strategies to Augment Muscle Carnosine
Strategies to optimize muscle carnosine synthesis through β-alanine supplementation seem to be of vital importance because carnosine has been reported to be a determinant of rowing performance (4) and contribute to the latter half of high-intensity sprint cycling (101). Furthermore, the increase in muscle carnosine content after β-alanine supplementation has been positively correlated (R = 0.498; p = 0.042) to the magnitude of performance improvement during a 2,000-m rowing time trial (4), and further improvements in high-intensity cycling capacity have been shown after 10 weeks of β-alanine supplementation compared with 4 weeks (44). It would therefore seem important to maximize muscle carnosine loading through β-alanine supplementation.
The increase in muscle carnosine after β-alanine supplementation is a robust and reproducible finding in both trained and untrained subjects after dosing protocols ranging from 1.6 to 6.4 g·d−1 for a period of 2–10 weeks (4,26,44,95). Within this range, the increase in muscle carnosine concentration seems to occur in a dose-dependent manner with the total amount of β-alanine consumption being the major causative factor on the subsequent increase in muscle carnosine concentration. This has stemmed from observations by Stellingwerff et al. (95) who reported a high linear dependency (R2 = 0.921) based on the total amount of β-alanine consumed, when either a high (3.2 g·d−1) or low (1.6 g·d−1) dose regimen was consumed. There was a ∼2-fold greater increase in muscle carnosine content in both muscle groups measured for the high dosing group (tibialis anterior: 2.04 mmol·kg−1 wet weight and gastrocnemius: 1.75 mmol·kg−1 wet weight increase) compared with the low dosing group (tibialis anterior 1.12 mmol·kg−1 wet weight and gastrocnemius 0.80 mmol·kg−1 wet weight increase).
These findings would appear to make the prescriptive application of β-alanine quite simple because of the apparent linearity between the total amount of β-alanine consumed and the increase in muscle carnosine content. However, the daily dose of β-alanine was limited in early studies because doses larger than ∼800 mg (∼10 mg·kg−1·BM−1) were accompanied by moderate to severe paresthesia symptoms (42). The mechanism behind β-alanine–induced paresthesia has been recently investigated by 2 studies, which intradermally injected β-alanine (66) or orally ingested a 3 g dose of β-alanine (68). These studies indicated that the skin sensations evoked by β-alanine ingestion are mediated by MrgprD expressed in cutaneous sensory neurons. Some studies have attempted to circumvent these undesirable symptoms by using multiple doses (<800 mg) of β-alanine (sometime as many as 8 doses) throughout the day to achieve the desired total β-alanine dose daily (4). More recently, the ingestion of a 1.6 g “slow-release” β-alanine formulation has been shown to alleviate perceived side-effects compared with the ingestion of a 1.6 g dose of pure β-alanine, which may allow for larger daily doses to be ingested throughout a supplementation period (24). Despite this recent finding, participants are still reporting symptoms of mild paresthesia after the ingestion of 1.6 g of slow-release β-alanine (10 of 22 swimmers supplementing with slow-release β-alanine). Furthermore, β-alanine is a common ingredient in preworkout supplements (38,91). However, the effect of β-alanine–induced paraestheia on exercise performance has not yet been investigated.
Although the increase in muscle carnosine content after β-alanine supplementation is a universal finding, there is a considerable interindividual variability in response to β-alanine supplementation (96). The variation in muscle carnosine synthesis in response to β-alanine supplementation among individuals is large (4,26,44). This variable response may relate to the inability of an individual to absorb β-alanine from the gut into the blood or an inability of the muscle to take up β-alanine. The variability in carnosine loading in response to β-alanine supplementation has led to individuals being categorized into low- and high-responders (7). Baguet et al. (4) reported a positive correlation between high baseline muscle carnosine content and the increase in muscle carnosine after β-alanine supplementation in elite rowers. Conversely, Stellingwerff et al. (95) reported no statistically detectable effect between baseline carnosine levels and subsequent muscle carnosine increases. However, these differences may be in part because of the exclusion of subjects with high initial muscle carnosine content (95) and the different muscles used to assess carnosine levels (4). However, until it is determined what the maximal attainable muscle carnosine levels are with prolonged β-alanine supplementation, correlations with baseline carnosine content need to be treated with caution. Furthermore, it would presumably be important to employ a dose relative to body mass or even lean body mass when loading with β-alanine because it would ensure that individuals with differing body compositions would be receiving a similar proportion of β-alanine, which may alleviate the large interparticipant variability in carnosine loading.
One recent study (93) sought to quantify the effects of coingesting β-alanine with a meal containing carbohydrates and protein on carnosine loading and the distribution of β-alanine in the body. The authors observed that carnosine loading was significantly improved after the coingestion of pure β-alanine with a meal (+64%) compared with in-between meals (+41%). However, there seemed to be no superior benefit when comparing chronic slow-release β-alanine supplementation with the pure form of β-alanine. A further observation from the study was that whole body retention of slow-release β-alanine is very high (97–98%) and only a very small portion (1–2%) is lost through urinary excretion, therefore, only a small amount is being converted into muscle carnosine (∼3%), which raises the question: what is the alternate fate of β-alanine? The authors speculated that the excess available β-alanine may be oxidized and contribute to total energy delivery. Admittedly, the contribution of amino acids to skeletal muscle energy provision is quite low. However, depending on the duration and intensity of the exercise bout, amino acid oxidation can provide from a few to ∼10% of the total energy expenditure (17). Alternatively, uptake of β-alanine into nonmuscle tissue, such as nervous tissue, may also account for a portion of the available β-alanine after ingestion (15). However, the alternate fate of β-alanine is unknown and, therefore, warrants future investigation.
In summary, human research has suggested that β-alanine supplementation (1.6–6.4 g·d−1) for a period of 2–12 weeks increases muscle carnosine content in a dose-dependent fashion, which is largely dependent on the total amount of β-alanine consumed. Most studies employed absolute doses of β-alanine, not basing the amount supplemented on body weight. Exceptionally, Bellinger et al. (12) employed a daily β-alanine dose of 65 mg·kg−1 BM·d−1 in an attempt to limit side-effects for smaller athletes, and Ducker et al. (30) who employed a relative β-alanine dose of 80 mg·kg−1 BM·d−1 presumably to maximize β-alanine intake in larger athletes. Daily doses larger than 6.4 g·d−1 are yet to be examined, and a maximal muscle carnosine threshold is yet to be identified from a prolonged β-alanine supplementation study.
Carnosine Washout After Cessation of β-Alanine Supplementation
The washout profile of augmented muscle carnosine content after β-alanine supplementation is also of great interest because it has a direct impact on the applicability of crossover-designed research studies and practical considerations for coaches and athletes because potential exercise performance improvements, attributed to the augmented carnosine levels, may remain after the cessation of β-alanine supplementation.
Carnosine degradation has been shown to be a relatively slow process with a reported washout rate of ∼2–4%·per week after the cessation of β-alanine supplementation (7,95). Furthermore, similar to carnosine loading, there seems to be considerable variability in the rate of carnosine washout, as Baguet et al. (7) reported a total washout period of 6–15 weeks, whereas Stellingwerff et al. (95) demonstrated a 15–20 weeks of washout period. The variability in the rate of carnosine washout between these studies may be because of methodological differences (exclusion of participants with high baseline carnosine levels (95)), addition of soleus carnosine measurements (7), the magnitude of carnosine augmentation, or the total number of participants (Baguet n = 8, Stellingwerff n = 21). The difference in washout rate between the 2 studies may also suggest that a regulatory influence regarding carnosine degradation may exist. Physical activity is one factor that has been postulated to contribute to the rate of muscle carnosine elimination (7,72). An animal experiment has suggested that carnosine is actively secreted by skeletal muscle during exercise (72). However, evidence from Baguet et al. (7) does not support the notion of a large net release of carnosine during exercise because of a lack of correlation between physical activity level and washout rate (R = 0.331; p = 0.469) in the study participants.
Carnosine can be hydrolyzed by at least 2 types of dipeptidases, serum, and tissue carnosinase (106). The absence of the latter from different types of human and animal skeletal muscle (74) may account for the slow carnosine degradation in humans. However, it remains to be determined which causative factors exist that explain the variability in the rate of carnosine elimination from skeletal muscle after the cessation of β-alanine supplementation.
Effect of Training on Muscle Carnosine
Repeated exposure to high-intensity exercise results in intramuscular adaptations, which may provide an improved resistance to fatigue and enhanced performance in anaerobic bouts of exercise (39,65). It has been recognized that a portion of this training effect may include an increase in muscle buffer capacity, which could effectively attenuate fatigue by moderating the effects of acidosis on the muscle (32). However, research to date has failed to show any augmentation of skeletal muscle carnosine after short-term training interventions (<16 weeks).
There is some indirect evidence to suggest that chronic prolonged training may increase carnosine synthesis. Parkhouse et al. (75) reported the vastus lateralis carnosine content of 800-m track runners (4.93 ± 0.76 mmol·L−1) and rowers (5.04 ± 0.72 mmol·L−1), who regularly undertake high-intensity bouts of training, was significantly higher compared with marathon runners (2.80 ± 0.74 mmol·L−1) and untrained individuals (3.75 ± 0.86 mmol·L−1). Furthermore, Tallon et al. (105) observed the carnosine content of resistance-trained bodybuilders to be twice that of untrained subjects. Both studies postulated that the elevated levels of muscle carnosine displayed in these athlete populations may have been a consequence of regular exposure to extreme muscular acidosis. However, in the case of Tallon et al. (105), the use of androgen-anabolic steroids, which the bodybuilders freely admitted to use, a change in diet, or the use of dietary supplements may have enhanced the muscle carnosine levels. Although evidence from these cross-sectional studies somewhat support the hypothesis that repeated exposure to high-intensity training may lead to the augmentation of muscle carnosine content (75,105), training intervention studies (4–16 weeks) have not supported this supposition (5,58,59,61,70).
Mannion et al. sought to examine the effects of 16 weeks (3 days per week) of isokinetic training consisting of 6 sets of 25 maximal repetitions with 30-second rest between sets or 5 sets of 15 maximal repetitions with 40-second rest between sets. The authors reported a small nonsignificant improvement in quadriceps isometric maximal voluntary contraction and a significant increase in 30-second cycling performance. However, this was not accompanied by an increase in muscle carnosine content (70). Similarly, Kendrick et al. (58,59) found no effect of 10 weeks of strength training or 4 weeks of isokinetic training on muscle carnosine content. Exceptionally, Suzuki et al. (102) reported a radical change in muscle carnosine content after 8 weeks of sprint cycling training. The untrained subjects doubled their muscle carnosine after 8 weeks of sprint training consisting of 1–2 Wingate cycling sprints (30 seconds) on 2 occasions each week. In contrast, Baguet et al. (5) found no change in carnosine content in response to a similar 5-week sprint cycling training intervention, which further isolates the findings of Suzuki et al. (102).
This evidence raises the question if the higher carnosine content observed in resistance-trained athletes, sprinters, and rowers was a result of chronic training, a diet consisting of foods high in β-alanine, or a consequence of genetic endowment and self-selection for competitive events demanding a high intracellular H+ buffering capacity. It could be argued that the training regimens employed by these training intervention studies (5,58,59,61,70) may not contain a sufficient training volume to induce adaptations to augment carnosine content. Training loads of competitive rowers, who display significantly higher baseline carnosine levels compared with endurance athletes and untrained individuals, reach 190 min·d−1 in high-load phases and ∼108 min·d−1 (94) in the tapering phases, which far exceeds the training loads in these studies (5,58,59,61,70). Interestingly, although not intended to be a training intervention study, Derave observed a significant increase in gastrocnemius carnosine content (+16%) in the placebo condition in a group of trained sprinters. The intervention period lasted for 4 weeks, at which time the sprinters were preparing for the indoor competition season and performed, on average, 5.4 training sessions per week with the relative percentage of total training time spent on power, speed, resistance, and endurance being 25, 23, 24, and 28% (similar to the β-alanine group). No further information on training load was provided so it is difficult to determine the effect that training alone had on carnosine content. Further research is required to be undertaken incorporating more robust chronic training interventions (>16 weeks) with large training loads in the population of trained athletes.
The Effect of β-alanine Supplementation on Exercise Performance
Time-to-Exhaustion and Laboratory-Based Exercise Protocols
The use of tests of exercise capacity to assess the effects of β-alanine supplementation has commonly been used in previous research. Although the relevance of exercise capacity tests has been questioned (22), time-to-exhaustion exercise protocols can be used in the laboratory to determine the mechanisms that may assist in explaining the responses to enhanced exercise performance. In the context of β-alanine supplementation, employment of exercise capacity tests may be able to effectively explore the mechanisms that explain the effect of augmented carnosine content on the physiological systems and metabolism during exercise.
Previous research has investigated the effects of β-alanine supplementation on parameters of exercise performance during incremental exercise tests to exhaustion. Stout et al. (98) observed a significant increase in ventilatory threshold, physical working capacity at fatigue threshold, and time to exhaustion of 13.9, 12.6, and 2.5%, respectively, in untrained women after 28 days of β-alanine supplementation (3.2–6.4 g·d−1). The effect of β-alanine supplementation on the onset of blood lactate accumulation in running performance has been investigated by Jordan et al. (57). The study involved 17 men who were randomly assigned to supplement with β-alanine (6.0 g·d−1) or a placebo for 28 days. β-alanine supplementation was effective in delaying the onset of fatigue by delaying the onset of blood lactate accumulation and increasing the percent of V[Combining Dot Above]O2max occurring as the onset of blood lactate accumulation. This finding is in line with the previous research from Zoeller et al. (113), who reported a significant improvement in the power output at lactate threshold after 4 weeks of supplementation with β-alanine. However, this finding was potentially misleading because there was also a significant decrease in V[Combining Dot Above]O2max in the β-alanine group. The authors did not provide any proposed physiological mechanism behind the decrease in V[Combining Dot Above]O2max, and training was not recorded throughout the supplementation period, so the reason for this remains unknown.
Hill et al. (44) investigated the effects of 4 and 10 weeks of β-alanine supplementation on cycling performance in a cycling time-to-exhaustion protocol at the intensity equivalent to 110% V[Combining Dot Above]O2peak. Four weeks of β-alanine supplementation resulted in a significant increase in the total work done (+13%), and a further 3.2% improvement in the total work done after 10 weeks of supplementation. This finding was confirmed by Sale et al. (81), who showed a 14.6% improvement in the total work done in a similar time-to-exhaustion protocol (cycling to exhaustion at 110% V[Combining Dot Above]O2peak) after 4 weeks of β-alanine supplementation. The identical β-alanine loading protocol was also able to significantly improve time to exhaustion during an isometric endurance test of the knee extensors contracting at 45% of maximal voluntary isometric contraction force (79). A recent study has also shown a performance enhancing effect of β-alanine supplementation by demonstrating a significant increase in isokinetic average power/repetition during a single bout of 30 isokinetic contractions at 180°·s−1, (β-alanine: +6.8 ± 9.9 W, placebo: −4.3 ± 9.5 W, p = 0.04, 85% likely benefit) (54).
In summary, the weight of evidence suggests that β-alanine supplementation improves exercise capacity, despite a recent study reporting no improvement in time to exhaustion in short (140% V[Combining Dot Above]O2max = ∼1 minute) and long (115% V[Combining Dot Above]O2max = ∼2–3 minutes) tests of sprint running endurance (55). The authors reported that the lack of ergogenic effect after β-alanine supplementation may have been related to the mode of exercise (running compared with cycling protocols employed in other studies), participants restricting energy intake and compromising performance during postsupplementation testing or an increased training intensity during the supplementation period, which may have masked the ergogenic effects of β-alanine displayed in the postsupplementation performance trials. Nonetheless, in a recent meta-analysis, Hobson et al. (49) reported that β-alanine supplementation significantly improves tests of exercise capacity (p = 0.013), showing a moderate effect size compared with placebo. It could be argued that an improvement in exercise capacity at supramaximal intensities would have little relevance to a population of trained athletes competing in competitive racing events (22). A time-trial protocol would appear to be more of a logically valid simulation of race events such as cycling or running because it is an actual event, whereas there is no sporting event that requires an individual to exercise at a set intensity until exhaustion, which is required in a time-to-exhaustion test. However, an improvement in exercise capacity may also be of interest to the population of trained athletes because this population regularly undertakes training sets that are implemented to maximally stress exercise capacity. If performance in the “exercise capacity training sets” can be repeatedly enhanced during training, effectively enabling athletes to train harder, the increased training dose may lead to enhanced training adaptations and, therefore, performance.
High-Intensity Repeated Effort Exercise Protocols
A recent avenue of research has been directed at the ergogenic potential of β-alanine supplementation to enhance high-intensity intermittent exercise. During repeated bouts of high-intensity exercise, the contribution of creatine phosphate and muscle glycogen to ATP turnover declines, and although there is an increase in the aerobic contribution to exercise (14), reduced power output, and total work production result (71,92). The decline in exercise performance has been shown to be related to the concomitant increase in H+ (40), suggesting that an enhanced ability to attenuate the rise in H+ may delay the fatigue process and enhance performance in high-intensity intermittent exercise.
Although the fatigue-inducing accumulation of H+ concentration and the combination of speed and endurance associated with this type of exercise suggests a potential benefit from β-alanine supplementation, research to date shows equivocal results. For instance, Saunders et al. (83) reported that 12 weeks of β-alanine supplementation significantly improved YoYo intermittent recovery test performance in amateur footballers. Performance in the YoYo intermittent recovery test has been closely related to the football match performance, because YoYo test performance outcomes are correlated with high-intensity running and total distance covered during a football match for top class referees (62) and footballers (63). Furthermore, the highest distance covered in a 5-minute period during a game has also been associated with YoYo IR2 performance (8), which provides an important application for these promising findings in terms of translating these improvements to performance of team-sport athletes during match play. However the exercise protocol may be a valid physiological simulation of match play, the performance measure is a run to exhaustion, which certainly does not represent soccer match play. More recently, Tobias et al. (107) examined the effect of β-alanine supplementation on high-intensity intermittent upper-body performance in well-trained experienced judo and jiu-jitsu competitors. Before and after 4 weeks of supplementation, competitors completed four 30-second upper-body Wingate tests, separated by 3 minutes. Compared with the presupplementation performance trial, the β-alanine group significantly improved average power output in the second (+6.5%; p = 0.042) and third (+10.5%; p = 0.013) set and a trend towards a significant performance improvement in the fourth set (+7.2%; p = 0.10). Furthermore, β-alanine supplementation significantly improved peak power output in the second (+7.7%; p = 0.097) and third set (+9.4%; p = 0.076).
In contrast, β-alanine supplementation was shown to have no effect on running performance in the Loughborough Intermittent Shuttle test (82). However, neither placebo or β-alanine group showed a performance decrement before supplementation, which may have masked any potential benefit from increased muscle buffering capacity because of β-alanine supplementation. Smith-Ryan et al. (85) aimed to evaluate the effects of β-alanine supplementation on high-intensity running performance by performing 3 high-speed runs to exhaustion at 90, 100, and 110% of peak velocity with 15-minute rest between bouts. There appeared to be no ergogenic benefit on time to exhaustion, critical velocity, or anaerobic running capacity at all 3 running intensities. The absence of any benefit could be attributed to the large rest times between sprints (15 minutes), allowing for adequate recovery and thereby preventing any ergogenic benefit in bouts 2 and 3 from the enhanced buffering capacity. Furthermore, the male placebo group showed a superior improvement in the run to exhaustion at 90 and 100% of peak velocity, which may have been a result of surplus exercise over the supplementation period contributing to the improved postsupplementation performance trials. However, this is purely speculative because exercise training was not recorded during the 4-week supplementation period. Hoffman et al. (51) also observed no significant difference in sprint times or fatigue rates in American football players in an intermittent shuttle running line drill (3 × 35–43 seconds with a 2-minute rest) after 3 weeks of β-alanine supplementation.
High-intensity intermittent exercise that is interspersed with smaller recovery periods (usually ≤60 seconds) and features short-duration sprints (≤10 seconds) has been termed repeated sprint ability (37). These short-duration sprints and recovery periods are thought to be indicative of the physiological demands of play in team-sport matches (90). Recent research has reported limited benefits of β-alanine supplementation on repeated sprint ability. Sweeney et al. (104) reported no ergogenic benefits in a repeated sprint protocol requiring recreationally active participants to complete 2 sets of 5 × 5 seconds of sprints separated by 45-second rest and a 2-minute recovery between sets. However, the extensive rest periods between sprints may have allowed the participants to adequately recover before commencing the next sprint, thereby reducing the accumulation of H+ and attenuating the contribution of muscular acidosis to fatigue. More recently, Ducker et al. (28) sought to determine the effects of 4 weeks of β-alanine supplementation (80 mg·kg−1 BM·d−1) on a repeated sprint protocol requiring team-sport athletes to undertake 3 × 6 20-m sprints with shorter recovery periods (25 seconds) between sprints and 4 minutes of active recovery between sets, which would seem to be more applicable to the requirements of team-sport match play (90). The authors reported marginally improved repeated sprint times (sprints 10, 11, and 18) with a likely benefit in sprint 18 after β-alanine supplementation. Further research is warranted to establish the ergogenic potential of β-alanine supplementation in highly trained team-sport athletes performing repeated sprint exercise that closely resembles the physiological demands of game play.
Time Trial and Sports Performance in the Field
Several studies have examined the potential ergogenic effects of β-alanine supplementation on sport-specific trials and in “real world” performance situations. A highly practical study reported a significant improvement in sprint cycling performance after an endurance ride with β-alanine supplementation (109). Seventeen moderately to well-trained cyclists supplemented for 8 weeks on either β-alanine (n = 9) (2–4 g·d−1) or a placebo (n = 8). The pre- and post-supplementation testing consisted of a 110-minute simulated road race consisting of varying intensities of 50–90% of maximal lactate steady state. The 110 minutes of simulated road race was then followed immediately by a 10-minute time trial, a 5-minute recovery, and finally, a 30-second all-out sprint. During the final sprint after the time trial, the β-alanine group had an increase in peak and mean power output by 11.4% (95% confidence interval [95% CI] = +7.8 to +14.9%) and 5.0% (95% CI = +2.0 to +8.1%), respectively during the 30-second maximal sprint.
More recently, Ducker et al. (29) sought to investigate the effects of 4 weeks of β-alanine supplementation (80 mg·kg−1 BM·d−1) on 800-m track running performance in recreational club runners. Postsupplementation race times were significantly faster after β-alanine (p = 0.02) with post- versus pre-supplementation race times being faster after β-alanine supplementation (−3.64 ± 2.70 seconds, −2.46 ± 1.80%), but not placebo (−0.59 ± 2.54 seconds, −0.37 ± 1.62%). These improvements were supported by a very likely (99%) benefit in the β-alanine group after supplementation. De Salles Painelli et al. (23) examined the effect of 5 weeks of β-alanine supplementation (3.2 g·d−1 for 7 days, then 6.4 g·d−1 thereafter) on 100- and 200-m swimming performance in well-trained state-level junior swimmers. In the 100-m trial, absolute changes in performance from pre- to post-supplementation in the β-alanine group (−2.1%; −1.30 ± 1.37 seconds) approached statistical significance (p = 0.07) compared with the placebo group (+0.3%; +0.26 ± 1.80 seconds). In the 200-m trial, absolute changes in performance were significantly faster (p = 0.002) in the β-alanine group (−2.0%; −2.81 ± 1.58 seconds) compared with the placebo group (−0.1%; −0.05 ± 2.43 seconds). Individual data from this study show that all 9 swimmers in the β-alanine group swam faster in the 100-m trial and 8 of the 9 athletes swam faster in the 200-m trial, which is likely to have a worthwhile positive effect in a competitive setting. Furthermore, Donovan et al. (27) demonstrated that β-alanine supplementation improved punch force and frequency (and hence accumulative punch force) in amateur boxers during the last 10 seconds of a simulated boxing contest consisting of 3 × 3 minutes of rounds (interspersed with 60-second rest). However, it must be acknowledged that these studies involved moderately trained athletes, and the magnitude of the ergogenic effect may not translate to elite athletes.
In contrast, Chung et al. (21) were unable to detect any substantial physiological or performance benefits after 10 weeks of β-alanine supplementation on competition swimming performance (50–200 m) in subelite/elite swimmers. Swimmers were supplemented with either β-alanine (4 weeks loading phase of 4.8 g·d−1 and 3.2 g·d−1 thereafter) or placebo for 10 weeks. Competition performance times were evaluated presupplementation (National Championships) and postsupplementation (national selection meet). There was an unclear effect (0.4%; ±0.8%; mean, ±90% confidence limits [90% CLs]) of β-alanine on competition performance compared with placebo with no meaningful changes in blood chemistry. Chung et al. (20) also found no benefit in longer duration cycling time trial performance after 6 weeks of β-alanine (6.4 g·d−1) in trained cyclists/triathletes. Both groups performed worse in the 1-hour postsupplementation cycling trial with the placebo group (60.6 ± 4.4 to 63.0 ± 5.4 minutes; p < 0.01) and β-alanine group tending to be slower (59.8 ± 2.8 to 61.7 ± 3.0 minutes; p = 0.069). Similarly, Derave et al. (26) reported no effect on 400-m running performance in trained sprinters after 4 weeks of β-alanine supplementation.
β-alanine supplementation did not produce a significant ergogenic effect in these sport-specific trials (4,12,30,48,54). Baguet et al. (4) reported a 2.7-second improvement in 2,000-m rowing ergometer performance in elite Belgian rowers after 7 weeks of β-alanine supplementation. This finding is consistent with Ducker et al. (30) who reported a 2.9-second improvement after 4 weeks of β-alanine supplementation. Although rowers supplementing with β-alanine in these studies were faster than previous supplementation, rowers in the placebo condition were 1.8 and 1.2 seconds slower. These results only approached significance (p = 0.07 and 0.055) and were not supported by large effect sizes (d = 0.2) or likely smallest worthwhile change values (49% possible chance of benefit) in the study of Ducker et al. (30). Similarly, Hobson et al. (48) recently reported a 1.8-second improvement after 4 weeks of β-alanine supplementation, which was very likely to be beneficial to 2,000-m rowing performance with the placebo group slowing by 4.5 seconds (a difference of 6.4 ± 8.1 seconds; between the response to β-alanine and the response to placebo). Furthermore, in the study of Bellinger et al. (12) and Howe et al. (54), β-alanine supplementation was associated with a 1.6% ± 1.7% (5.1 ± 8.4 W; 37% likelihood; p = 0.20) and 1.7% ± 1.8% (6.5 ± 7.3 W; 44% likelihood; p = 0.25) improvement in 4-minute cycling time trial performance, respectively. Collectively, these data suggest that the ergogenic potential of β-alanine supplementation for highly trained athletes still remains equivocal, but may provide a practical worthwhile benefit in some measures of sport-specific competition. However, the relatively large SDs shown for these differences suggest that an individual response to β-alanine supplementation may be evident in the population of trained athletes.
Other factors that may account for the discrepancies in studies of β-alanine supplementation in highly trained and elite athletes competing in real-world performance is the inherent variability of competitive performance because of the influence of factors such as prior training, cumulative fatigue, diet and pacing strategies employed in time trial, and constant duration protocols, which may mask any potential benefit of β-alanine supplementation on performance (45,108). Furthermore, the constraints associated with studying a highly trained or elite athletic population poses difficulty because they are a scarce resource, and intervention-based research designs often conflict with their commitments to training and competition. Moreover, a number of authors have drawn conclusions based solely on the statistical significance of the effect of β-alanine supplementation on exercise performance without considering the magnitude of the effect, which is considered important when investigating worthwhile changes in athletic performance (53). The failure of a number of studies to report an error of measurement or CLs that apply to the variation in performance of the particular exercise test that was employed also confounds the literature investigating the ergogenic potential of β-alanine supplementation. Because the magnitude of performance improvement after β-alanine supplementation is likely to be around 1–3%, experimental designs and interpretation of results in research studies require careful consideration.
When monitoring the change in performance after β-alanine supplementation, it is important to take into account the magnitude of the smallest worthwhile enhancement in performance and the uncertainty or noise in the test result (52). Noise in a test result is best expressed as the typical or standard error of measurement derived from the difference in performance between multiple trials. When expressed as a percentage of mean performance, the SD is known as the coefficient of variation (CV). An enhancement of performance much smaller than the CV cannot be considered a real change because the difference in the dependent test variable may simply be because of the natural variation in performance. Alternatively, enhancements in performance much larger than the CV will provide an assured improvement in performance. The enhancement that begins to make a difference to an athlete's performance is somewhere in between these 2 extremes, similar to the magnitude of the CV. Furthermore, the noise in most performance tests is greater than the smallest worthwhile difference, so assessments of changes in performance can be problematic (52). It is therefore important to report the CV as a representation of the natural variation in performance among the study group of participants. To establish the true effects of β-alanine supplementation on exercise performance for different types of athletes, it would be recommended that researchers design their studies to include multiple trials pre- and post-supplementation, report the 95% CLs for the dependant variable, interpret the CLs and the magnitude of the outcome in terms of the likely effect on performance, and establish the characteristics that might account for the individual differences in response to β-alanine supplementation (Table 1).
β-alanine Supplementation as a Training Aid
Nutritional supplementation for athletes is not only beneficial in competition; it may also be functional to facilitate training by allowing an athlete to train harder and therefore achieve superior levels of training adaptation. This avenue of thought is based on the assumption that the adaptation to repeated bouts of training occurs during the recovery period and that if an individual can train harder, the adaptation will be greater. Theoretically, augmentation of muscle carnosine, presumably increasing the ability to perform high-intensity exercise during training, may lead to greater training adaptations over a specific training period. Consequently, several studies have investigated the effects of combined β-alanine and training on subsequent training adaptations and exercise performance (21,50,51,58,60,87,88).
Kendrick et al. (58) reported no additive benefit of β-alanine supplementation (6.4 g·d−1 for 10 weeks) compared with resistance training alone on whole body strength, isokinetic force production, muscular endurance, and body composition. Similarly, Walter et al. (111) reported no added benefit of β-alanine supplementation compared with high-intensity interval training alone on V[Combining Dot Above]O2peak during a graded cycling exercise. Smith et al. (87) reported no additional benefit on neuromuscular fatigue or muscle function compared with training alone after 6 weeks of β-alanine supplementation and high-intensity interval training. Participants engaged in a total of 6 weeks of high-intensity interval training consisting of 5–6 bouts of a 2:1 minute cycling work to rest ratio while supplementing with 3–6 g·d−1 β-alanine. After the intervention period, the authors reported similar significant reductions in neuromuscular fatigue during cycling exercise in both training groups. The authors concluded that high-intensity training appeared to be the primary stimulus effecting neuromuscular fatigue, and that adaptations from the training intervention may be more influential than augmenting muscle carnosine on delaying fatigue in recreationally active men.
The same research group further examined the effects of the same training and supplementation regimen on parameters of endurance performance (88). After the 6 weeks of training and supplementation intervention, the β-alanine group displayed significantly larger improvements in maximal oxygen uptake and the time to reach maximum oxygen consumption. In addition, total work done in a maximal cycling test set at an intensity corresponding to 110% of V[Combining Dot Above]O2peak workload was significantly increased during the last 3 weeks by 32 and 18% for the β-alanine and placebo groups, respectively. Furthermore, although not significant, participants in the β-alanine group consistently trained at higher workloads (intensity) and for longer time periods (volume) during the supervised interval training sessions according to the participants training logs. The ability of the β-alanine group to consistently train at higher intensities during the training and supplementation period may have been a consequence of the presumed augmentation in muscle carnosine after β-alanine supplementation, and this may explain the further improvements in endurance performance after intervention.
Three studies have investigated the application of β-alanine supplementation as a training aid in team-sport athletes (50,51,60). Kern and Robinson (60) supplemented American football players and collegiate wrestlers with β-alanine (4.0 g·d−1) during an inseason 8-week period of high-intensity interval training. The authors reported larger gains in lean body mass and positive trends towards a superior performance in a 300-yard shuffle run and flexed arm hang time after the training and β-alanine supplementation period. Furthermore, Hoffman et al. (51) reported an increase in preseason training volume (∼9%) in collegiate footballers supplementing on β-alanine for 30 days. β-alanine supplementation may also be an effective training aid in the off-season period (50). Hoffman et al. (50) compared the combination of β-alanine and creatine with creatine alone during a 10-week off-season conditioning program in collegiate football players. The addition of β-alanine to creatine promoted superior adaptations in lean tissue accruement and body fat decrements, as well as enhancing training volume more so compared with creatine supplementation alone. However, the true effects of β-alanine were unable to be quantified because the study design did not include a β-alanine–only group. These results appear to support the efficacy of β-alanine supplementation as a training aid and highlight the requirement for longer-term well-controlled training studies.
One recent highly practical study sought to investigate the effectiveness of β-alanine supplementation on training in an applied real-world setting of swim training and competition (21). Chung et al. (21) supplemented 30 swimmers with β-alanine (4-week loading phase of 4.8 g·d−1 and 3.2 g·d−1 thereafter) or a placebo for 10 weeks. Swimmers completed 3 standardized training sets at baseline and after 4 and 10 weeks of supplementation. The training sets were distance-specific to each of the swimmers' competitive event (sprint, middle-distance, and distance) and consisted of repeated maximal 50-m efforts immediately followed by the distance-specific maximal effort. The authors noted a substantially greater improvement in training set performance after 4 weeks in the β-alanine group compared with the placebo group (−1.3 ± 1.0%; mean, ±90% CLs) but unclear effects after 10 weeks (−0.2%; ±1.5%). Despite the authors reporting weekly training volumes for the entire group of swimmers (40 ± 4 km·wk−1), the study did not control or provide measures for training volume between the placebo and β-alanine group. Therefore, it is difficult to interpret whether the β-alanine group was able to consistently train at the higher intensities observed after 4 weeks of training and β-alanine supplementation. Future research should be designed to examine whether elevated carnosine levels from β-alanine supplementation might enable athletes to modify their training load and train at a higher intensity and increase their training volume, and therefore, achieve greater training adaptations, and indeed, performance. This area clearly warrants future research.
Combining β-Alanine With Other Supplements
Given the potential for improved exercise performance with chronic β-alanine supplementation, it would seem appropriate rationale that combining β-alanine with other ergogenic aids may provide an additive benefit. To maximize the potential ergogenic effect of supplement use, recent research has extended from the isolated supplementation of β-alanine to investigate possible additive effects with other supplements. Although it seems logical that 2 supplements that provide an independent ergogenic benefit to exercise performance would undoubtedly provide an additive effect when combined, this is not always the case, and supplements may be counterproductive when coingested (110). Therefore, the effect of β-alanine supplementation in combination with other ergogenic aids on exercise performance is warranted.
β-alanine and Creatine Monohydrate Supplementation
In light of this, β-alanine has been combined with creatine monohydrate in an attempt to investigate any potential synergistic effect on performance compared with either supplement alone (50,97,113). Hoffman et al. (50) investigated the effects of 10 weeks of β-alanine (3.2 g·d−1) and creatine monohydrate (10.5 g·d−1) on muscular strength, power, and body composition in collegiate football players. The authors reported superior improvements in fatigue rates, training volume, and body composition after the combined supplementation of β-alanine and creatine monohydrate supplementation compared with creatine alone. The addition of β-alanine to creatine appeared to have the greatest effect on lean tissue accruement, reducing body fat composition, and enhancing training volume more so than supplementing with creatine alone, although this observation needs to be treated with caution because the study design did not include a β-alanine–only group. The effect of combined β-alanine and creatine monohydrate has been investigated on aerobic cycling performance in 55 untrained men (113). The participants were randomly assigned to 1 of 4 groups: placebo (34 g dextrose; n = 13), creatine monohydrate (5.25 g creatine monohydrate + 34 g dextrose; n = 12), β-alanine (1.6 g β-alanine + 34 g dextrose; n = 14), or β-alanine and creatine monohydrate (5.25 g creatine monohydrate + 1.6 g β-alanine; n = 16). The supplements were ingested 4 times per day for 6 consecutive days, then twice per day for 22 days before postsupplementation testing. The combined ingestion of β-alanine and creatine was reported to improve indices of aerobic capacity to a larger extent compared with creatine or β-alanine supplementation alone (113). Stout et al. (97) employed the same dosing regimen and found a significant improvement in the physical working capacity at fatigue threshold in 51 untrained men; however, there was no additive effect of β-alanine and creatine monohydrate supplementation.
β-alanine and NaHCO3 Supplementation
More recently, research has administered concurrent β-alanine and NaHCO3 supplementation designed to enhance intra- and extra-cellular buffering capacity, respectively, with their combined actions potentially ameliorating the ergogenic effects of either supplement alone (12,23,28,48,81,107). Bellinger et al. (12) reported a minimal additive effect (p = 0.22) on performance (average power output) after the combined supplementation of β-alanine and NaHCO3 (+3.3%) compared with NaHCO3 (+3.1%) or β-alanine supplementation alone (+1.6%), despite 6 of the 7 cyclists improving their performance in the 4-minute cycling time trial. Similarly, Sale et al. (81) reported a further nonsignificant 4.1% improvement (p = 0.74) in time to exhaustion in a supramaximal cycling performance test (∼2.5 minutes) compared with β-alanine supplementation alone, with magnitude-based inferences suggesting the additive ergogenic benefit had a ∼70% probability of a meaningful positive difference.
De Salles Painelli et al. (23) also examined the potential additive effect of combined β-alanine and NaHCO3 supplementation by measuring the combined ergogenic effects on 100- and 200-m swim performance in trained junior swimmers. In the 100-m trial, all 7 swimmers further improved their swimming time after acute NaHCO3 ingestion combined with chronic β-alanine supplementation (average change, −1.4%; mean time, −0.76 ± 0.43 seconds; p = 0.29) compared with β-alanine alone. All 7 swimmers were also faster in the 200-m trial after the combined supplementation (average change, −0.63%; mean time, −1.18 ± 0.62 seconds; p = 0.21) compared with β-alanine alone. Furthermore, Hobson et al. (48) suggested a small (1.1 ± 5.6 seconds) but possibly beneficial additive effect in 2,000-m rowing ergometer performance when combining β-alanine with NaHCO3 supplementation compared with β-alanine alone in well-trained rowers.
Tobias et al. (107) further explored the ergogenic effects of combined β-alanine (6.4 g·d−1 for 28 days) and NaHCO3 (0.5 g·kg−1 SB for 7 days) supplementation on high-intensity exercise performance, employing an intermittent exercise protocol involving four 30-second upper-body Wingate tests (3 minutes of recovery between efforts) in well-trained judo and jiu-jitsu competitors. The main finding of this study was a significantly greater (p = 0.002) performance improvement (total work done) after the coingestion of β-alanine and NaHCO3 (+14%) compared with β-alanine (+7%) or NaHCO3 alone (+8%). This is the first study that has demonstrated a clear significant additive ergogenic benefit after the combined supplementation of β-alanine and NaHCO3. The main methodological difference between this study and previous work investigating the coingestion of β-alanine and NaHCO3 is the addition of a chronic NaHCO3 loading protocol and the type of exercise protocol employed. Tobias et al. (107) used an intermittent protocol requiring participants to complete a 4 bout (30-second bouts) upper-body Wingate test interspersed by 3 minutes of passive recovery periods. It has been suggested that intermittent supramaximal exercise promotes a considerably greater intramuscular acidosis than continuous high-intensity exercise and is more limited by muscle acidosis and, therefore, a greater potential to be improved by increased buffering capacity. Previous studies have employed single bout time to exhaustion or continuous fixed duration/distance exercise protocols (cycling, rowing, and swimming), which may have accounted for the absence of a significant additive ergogenic benefit.
Interestingly, Ducker et al. (28) recently observed that combining β-alanine and NaHCO3 supplementation (total sprint time 0.58 seconds faster) actually abraded the magnitude of performance improvement compared NaHCO3 ingestion alone (total sprint time 1.28 seconds faster) on repeated sprint exercise. These data suggest that 4 weeks of β-alanine supplementation counteracted the benefit of the enhanced [HCO3−] after acute NaHCO3 loading. Data available to date do not seem to provide a sound explanation of how enhanced carnosine content could impair the ergogenic potential of elevated bicarbonate buffering capacity, although the study had small participant numbers (n = 6) that may have confounded the results. Further investigations into the efficacy of combined supplement strategies for a range of exercise modes appear warranted to investigate whether β-alanine supplementation, in combination with other ergogenic aids, is synergistic, trivial, or counterproductive to exercise performance.
Mechanism of Action
Exercise performance benefits associated with β-alanine supplementation include increased peak power (109), muscular strength (50,51), time to exhaustion (44), delay in the onset of fatigue (97) and blood lactate accumulation (57), and a host of other physiological benefits (98). The improvement in these measures of exercise performance after β-alanine supplementation has been associated with the increase in muscle carnosine concentration. As carnosine has been implicated in a number of physiological actions, several explanations for the increase in performance are possible. The most likely would seem to be an increase in intracellular buffering capacity (11), protection against exercise-induced increases in reactive oxygen species (16), increasing calcium sensitivity in muscle fibers (64), protecting proteins against glycation by acting as a sacrificial peptide (47), and preventing the formation of protein–protein cross-links through reactions with protein-carbonyl groups (46). Of these, the former would presumably be more favorable. An increase in muscle buffering capacity is inevitable given the observed change in muscle carnosine content in response to β-alanine supplementation.
Enhanced Buffering Capacity
Although the direct cause of fatigue during high-intensity exercise still remains to be unequivocally determined, the contribution of muscular acidosis to the fatigue process has been repeatedly postulated as one of the major factors leading to a loss of force- or power-producing capacity in response to contractile activity (see review (77)). The proposed mechanism by which muscle acidemia is thought to contribute to muscular fatigue is uncertain; however, it has been suggested that it may slow glycolysis (43,100), impede calcium release from the smooth endoplasmic reticulum (34), disrupt the excitation-contraction coupling process (76), and increase the perception of fatigue (103). Although some studies have suggested that muscle acidemia has a minimal contribution to any decrement in performance (18,73), recent studies have demonstrated that muscle buffer capacity, in particular carnosine, is an important determinant of high-intensity exercise performance (4,13,101). This suggests that the ability to buffer H+ may be important for maintaining performance during high-intensity exercise.
Initial research contributing to the discovery of the physiological role of carnosine established a side chain pKa of 6.83, which may enable carnosine to play a vital role as a physiological buffer because it can readily accept protons during contraction-induced acidosis (9). Further evidence to support the role of carnosine as a proton buffer has stemmed from comparative studies assessing the buffering capacity of different species of animals. Studies with sea mammals demonstrated that deep sea fish, exposed to low O2 availability and therefore high muscle acidosis, display greater muscle carnosine content than non-deep sea fish (2). Moreover, Severin et al. (84) provided experimental support for the role of carnosine as an intracellular pH buffer by using isolated frog muscle to demonstrate that in the presence of carnosine, the muscle could accumulate large amounts of lactate without significant change in function. However, in the absence of carnosine, lactate contributed to the acidification of muscle tissue, resulting in fatigue in the isolated muscle. Observational studies in humans have also associated the role of carnosine as an intracellular buffer by identifying greater concentrations in type 2 fibers compared with type 1 fibers (44). Type 2 muscle fibers are more regularly exposed to acidotic environments because of their recruitment during high-intensity exercise and hence their need to possess a greater buffering capacity.
The role of carnosine has been shown to be of vital importance in the maintenance of intracellular pH during exercise, effectively providing a resistance to fatigue. This was observed by Suzuki et al. (101), who found a significant correlation between initial carnosine concentration and mean power per kg body mass in the final 10 seconds of a 30-second anaerobic Wingate test (21–25 seconds: R = 0.694, p ≤ 0.05 and 26–30 seconds: R = 0.660, p ≤ 0.05). These results suggest that initial muscle carnosine content is related to power output in the latter portion of a bout of high-intensity exercise. This finding is supported by Baguet et al. (4) who was reported a strong positive correlation between muscle carnosine content and performance over a rowing distance of 100, 500, 200 and 6,000 m (R = 0.6–0.7). These findings suggest that high carnosine concentrations relate to high-intensity exercise performance by possibly attenuating the fall in intramuscular pH associated during periods of short-duration high-intensity exercise.
Although a clear role for carnosine as a pH buffer has been established, the relative importance of carnosine to muscle buffering capacity has been questioned because it contributes a modest ∼6–7% to the intracellular buffering capacity in the human vastus lateralis muscle (69). However, this is likely an underestimate of carnosine's contribution to buffer capacity because of the technique employed, which overestimates the total muscle buffer capacity, and thus, underestimates the potential contribution of carnosine (70). Furthermore, after a period of β-alanine supplementation (4–6.4 g·d−1 for 4 weeks), the induced elevation in muscle carnosine concentration (∼60%) may increase the estimated buffering capacity to ∼14% (42). Moreover, carnosine is not evenly distributed in skeletal muscle, occurring in higher concentrations in type 2 fibers (41), which increases the contribution of carnosine to ∼17% of total buffering capacity and increases the emphasis of the physiological significance of augmentated carnosine content.
Accordingly, β-alanine supplementation should thereby improve the capacity for glycolytic energy production given that muscle acidosis may impair activity of key regulatory enzymes of glycolysis such as phosphorylase and phosphofructokinase (40). However, a limitation of current research is the lack of invasive measurements that would provide insight as to the potential mechanisms underpinning the exercise performance improvements reported in some β-alanine studies. A number of studies have reported blood lactate measurement during various exercise performance protocols; however, it is difficult to make accurate conclusions on muscle lactate kinetics based purely on the measurement of blood lactate per se, especially considering that studies have observed conflicting postexercise blood lactate concentrations with some studies showing a decrease in blood lactate (21) and an increase (27) in postexercise blood lactate concentrations that have been unaffected by β-alanine supplementation (81,109).
However, it could be speculated that an increased muscle carnosine content would attenuate the drop in intracellular pH during high-intensity exercise. The smaller trans-sarcolemmal concentration gradient of H+ would presumably decrease the acid efflux from the active muscle cells and result in a less pronounced circulating acidosis. This supposition is supported by Baguet et al. (6), who reported an attenuation in the decline in blood pH during a 6-minute high-intensity cycling exercise bout after 4–5 weeks of β-alanine supplementation. The improved buffering capacity resulting from augmented muscle carnosine content may increase the capacity for sustained high rates of glycolytic flux, which is evidenced by the increased lactate accumulation with β-alanine supplementation (27).
Enhanced Calcium Sensitivity
Other physiological roles ascribed to carnosine may also explain the mechanism behind the ergogenic benefit on exercise performance after β-alanine supplementation. The amount of Ca2+ released from the sarcoplasmic reticulum into the cytosol during muscle contraction has been outlined as a major factor contributing to muscular fatigue (3). Decreased Ca2+ release for binding to troponin will reduce the number of actomyosin complexes and reduce the force output by the muscle. Reductions in Ca2+ release have been shown to be mediated by alterations in the Ca2+ channels, primarily the ryanodine receptors (35), of which, carnosine has been thought to activate (10), thereby potentiating Ca2+-induced Ca2+ release (31). More recently, Everaert et al. (33) supplemented mice with either carnosine (0.1, 0.5, or 1.8%) or β-alanine (0.6 or 1.2%) in their drinking water for 8–12 weeks. After supplementation, soleus and extensor digitorum longus muscle were tested for contractile properties and carnosine content. The authors reported that supplementation with β-alanine (1.2%) markedly elevated carnosine levels (∼160%) and resulted in an increased fatigue resistance and a marked leftward shift of the force-frequency relation, and thus indirectly improving Ca2+ handling. In support, Dutka et al. (31) sought to characterize the effects of augmented carnosine content in human muscle fiber function. Fiber segments were obtained from the vastus lateralis, were mechanically skinned, and their Ca2+ release and contractile apparatus properties were characterized. The authors reported that augmented carnosine content in the muscle fibers increased the submaximal force output, which was attributed to an enhanced calcium sensitivity of the contractile apparatus in both type 1 and type 2 fibers. In practical terms, the increased muscle carnosine content aids muscle performance in both fiber types by increasing the Ca2+ sensitivity of the contractile apparatus and possibly also by aiding Ca2+ release, which may help to slow the decline in muscle performance during a fatiguing bout of exercise. Emerging evidence to support the role of augmented carnosine content, effectively increasing calcium sensitivity in muscle fibers, seems promising; however, the enhanced Ca2+ handling in the presence of elevated carnosine levels has only been established in vitro, the evidence in vivo is currently lacking.
In relation to an acute bout of exercise, free radicals have been hypothesized to affect muscle contractility (99), energy production (67), and subsequently contribute to fatigue during, or in subsequent physical performance (36). There is a great deal of uncertainty surrounding the need for dietary antioxidants and the role they play in supporting athletic performance. However, if the exercise-induced production of free radicals exceeds the antioxidant capacity of an individual, muscle and immune function can be impaired. Antioxidant supplementation may prevent this damaging increase in free radicals and, thus, antioxidant supplementation may provide a worthwhile benefit to the quality of training and competitive performance. Carnosine has been linked to a role as an antioxidant because of its ability to interfere with peroxidation reactions and its ability to protect cell membranes and other cell structures (16). Recently, Smith et al. (89) aimed to evaluate the effects of β-alanine supplementation on markers of oxidative stress in women. At the beginning and the end of the 28-day supplementation period, the women performed a graded oxygen consumption test to evaluate V[Combining Dot Above]O2max, time to exhaustion, ventilatory threshold, and establish peak running velocity, as well as perform an oxidative stress run lasting 40 minutes at 70% peak velocity. Before, immediately after, and in the 2–6 hours postrunning, the total antioxidant capacity, superoxide dismutase, 8-isoprostane, and glutathione were measured. After evaluation of the CIs and magnitude inferences, the authors suggested some potential for β-alanine supplementation, by way of augmented carnosine content, to act as an antioxidant, most clearly related to the reduction in lipid peroxidation, and thus, possible protection of biological membranes. The authors also observed a statistically significant reduction in the rating of perceived exertion from pre- to post-supplementation in the β-alanine group at the 40-minute mark of the oxidative stress treadmill run (p = 0.02). In a similar study design, Smith-Ryan et al. (86) reported that β-alanine supplementation had no influence on reducing baseline or exercise-induced oxidative stress in recreational active men. Nonetheless, further in vivo research is needed to elucidate the potential role of augmented carnosine content and its effect on oxidative stress resulting from exercise varying in intensity and duration.
The increase in muscle carnosine content induced by β-alanine supplementation is a universal finding, but only some studies report an enhancement in exercise performance. Currently, there is some scientific evidence that β-alanine supplementation provides meaningful worthwhile benefits for athletes competing in events involving sustained high-intensity exercise of 1–7 minutes duration or sprint performance at the end of endurance exercise, and therefore, athletes are encouraged to let individual experience dictate their use of β-alanine supplementation. β-alanine supplementation may also enable athletes to train at a higher intensity and increase their training volume during training sets that maximally stress exercise capacity. Because it is often the case with nutritional supplements, an individual analysis needs to be taken to determine whether β-alanine supplementation may be a worthwhile approach to improve training and competitive performance. At present, the research investigating the ergogenic potential of β-alanine supplementation on exercise performance is in its infancy with additional well-controlled investigations in an applied sporting setting required. This includes elucidating the type of sports and environments, where β-alanine supplementation may be most useful and refining the strategy on how it is supplemented, with particular focus on the length of supplementation protocols to allow coaches and athletes to make more informed decisions about employing β-alanine supplementation as a worthwhile ergogenic aid.
Coaches and athletes should consider the following practical recommendations when considering the use of β-alanine supplementation to enhance sports performance. (a) The use of β-alanine supplementation should be made on an individual basis, as although adverse performance effects are uncommon, not all athletes will benefit from supplementation. (b) Carnosine loading appears to be dose-dependent; therefore, to maximize carnosine loading, the total amount of β-alanine ingested should be on the upper limit of what is practical, while attempting to minimize the unpleasant side-effects of paresthesia. (c) Although it appears only small benefits are apparent to trained athletes, such small improvements may be worthwhile in real-world settings. (d) β-alanine supplementation may not only be beneficial to competitive performance, but also employed as a training aid to augment high-intensity bouts of exercise. (e) Care should be taken when evaluating results from the studies employing performance measures and participants unrelated to their field. The recommended daily dose of β-alanine that seems practical would be ∼80 mg·kg−1 BM·d−1, which should be divided evenly into <10 mg·kg−1·BM−1 doses throughout the day and ingested with meals to maximize carnosine loading.
The author has no conflict of interest. There were no external funding sources for this work.
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