Team sports such as soccer, field hockey, and Australian football are characterized by multiple repeated sprints, separated by short rest periods (38,39). Maintaining repeated-sprint ability (RSA) is a vital performance component in these sports. Typically, repeated-sprint requirements of team sports comprise several bouts of 6–7 sprints over a distance of 10–20 m (∼1.5–4 seconds), generally interspersed with ∼20–25 seconds of active recovery throughout a game (38,39). These repeated short sprints can lead to significant accumulation of H+, which can consequently impair exercise performance (10). Therefore, any increase in the level or functioning of the buffering systems of the body, including amino acids, proteins, inorganic phosphate, bicarbonate, creatine phosphate hydrolysis, and lactate production (33), could significantly attenuate the decline in blood and muscle pH and potentially lead to improved repeated-sprint performance.
Beta alanine (BA) (3-Aminopropionic acid, C3H7NO2) is a beta amino acid that has received recent research interest due to its potential positive effects on muscle pH and exercise performance when loaded with over several weeks. The level of BA is rate limiting for the production of carnosine (β-Alanyl-L-histidine, C9H14N4O3), a significant H+ buffer found within muscle fibers (pKa = 6.83). Specifically, supplementing with BA doses ranging from 3–6 g·day−1 (∼40–80 mg·kg−1·BM·day−1) for at least 4 weeks can lead to 30–80% increases in intramuscular carnosine concentrations (3,5,14,19,20,24,25), which can increase muscle buffer capacity and potentially improve exercise performance in events requiring significant energy contributions from anaerobic glycolysis (1,3,14,40,41,42). In addition, higher muscle carnosine concentrations may benefit exercise performance by increasing the sensitivity of muscle fibres and calcium release channels to calcium (7,16,17,27,34,44), by enhancing vessel vasodilatory effects (32), and by its antioxidant properties (26).
To date, studies investigating the effects of BA supplementation on RSA have reported little ergogenic effect (22,36,43). For example, Saunders et al. (36) found no benefit of BA supplementation in both elite and nonelite team-sport players performing the Loughborough Intermittent Shuttle Test. Sweeney et al. (43) also reported no improvement in average power output and total work done in healthy males completing sprints on a nonmotorized treadmill. However, the sprint duration (5 seconds) and rest times (45 seconds between sprints) used in this protocol were not typical of those seen in team-sport match play (38,39). Conversely, Hoffman et al. (22) reported a trend for a lower fatigue rate in American football players completing a repeated line drill after BA supplementation. Similar to the study of Sweeney et al. (43), their protocol also did not match the typical requirements of team-sport match play (38). Whether results would be different if exercise performance involves repeated short duration sprints separated by brief recovery times that typically characterize match play in team sports is unclear.
Ingesting an acute oral dose (0.3 g·kg−1 BM) of sodium bicarbonate (NaHCO3) 60–90 minutes before exercise increases the preexercise blood pH to 7.45 or greater and then delay the decline in pH associated with high-intensity exercise requiring significant anaerobic metabolism (10,11,29). To date, several studies have investigated the effects of supplementing with sodium bicarbonate on exercise trials that reflect the energetic requirements of team sports and have reported improvements in work done, power output, and a lower decline in repeated-sprint times (10,11,28,31).
Of interest is whether the combination of sodium bicarbonate (extracellular blood buffer) and BA (intracellular muscle buffer via carnosine) supplementation can lead to enhanced repeated-sprint performance beyond what is possible with either supplement alone. Recent research has found that combining sodium bicarbonate and BA supplementation together resulted in slightly improved high-intensity cycling performance (2–4 minutes), more so than when BA supplementation was undertaken alone (9,35). Therefore, the purpose of this study was to investigate whether supplementation of BA for 28 days combined with a pre-exercise dose of sodium bicarbonate, could improve prolonged repeated-sprint performance in team-sport athletes. We hypothesized that both BA supplementation and an acute dose of sodium bicarbonate would separately result in improvements in repeated-sprint performance, but that combining both treatments would lead to a greater improvement in RSA compared with either supplement alone.
Experimental Approach to the Problem
A randomized placebo-controlled study was conducted, which also incorporated duplicate (1 week apart) trials, performed both before and after 28 days of either BA or placebo (glucose) supplementation and a preexercise ingestion of either sodium bicarbonate or placebo. Duplicate trials were conducted to moderate any variation between trials and were performed at the same time of day to control for diurnal variations in exercise performance. Participants abstained from performing any vigorous exercise and from ingesting caffeine 24 hours before each trial and followed the same dietary intake on each testing day. Training diaries were completed 2 days before testing through to the completion of the study, whereas food diaries were completed for the 2 days before each testing session to ensure exercise and dietary compliance before each trial.
Twenty-four male competitive team-sport athletes, who were currently in the weekly competitive period of their respective seasons, were recruited to the study (Table 1). Participants from Australian football, hockey (field), and soccer were selected because of the similar physiological and match play requirements of each of these sports (6,13,15,38,39). They had not supplemented with any nutritional substances in the preceding 3 months or with BA for the previous 6 months. All participants were informed of the study requirements, benefits, and risks before giving informed consent. Approval for the study was granted by the research ethics committee of the University of Western Australia.
The repeated-sprint test (RST) was performed in an indoor gymnasium on a sprung wooden floor. Participants performed an individualized warm-up (similar to their pregame warm-up) that ranged from 5–10 minutes, which consisted of walking, jogging, sprinting, and dynamic stretching. Each individual warm-up was recorded and replicated in further trials. Two self-paced sprints (60 and 80% of maximal ability) were completed at the end of the warm-up to ensure readiness to sprint during the test.
The RST involved 3 sets of 6 × 20 m maximal running sprints, departing every 25 seconds, which included the time taken to jog back to the starting position. This distance and timing was chosen to mimic the mean sprint distance/time, recovery, and energy requirements of team sports (38). Sprint times were recorded using electronic timing gates (Fusion Sport Smartspeed, Coopers Plains, Queensland, Australia). Four minutes of active recovery was completed between sets (1 minute rest, 1 minute light jogging, 1 minute walking, and 1 minute rest) around a 20 × 20 m2. Sim et al. (37) completed the same protocol and reported typical error and coefficient of variation values for the total time taken to complete 1 set of sprints, best 20 m time, and percentage decrement of 0.060 seconds and 1.8%; 0.19 seconds and 1.1%; and 1.5% and 64.6%, respectively. Further, intraclass correlation (ICC), SEM, and minimal difference (MD) were calculated for each variable (total sprint time [TST] ICC = 0.91, SEM = 0.82, MD = 2.28; set 1/2/3 total time ICC = 0.85–0.92, SEM = 0.25–0.38, MD = 0.71–1.06; first and best sprint of each set ICC = 0.87–0.91, SEM = 0.04–0.06, MD = 0.12–0.18; percentage decrement ICC = 0.26–0.75, SEM = 0.91–1.62, MD = 2.52–4.50). Environmental conditions within the gymnasium were measured using a temperature/humidity meter (Fluke 971; Fluke Corporation, WA, USA) during each trial, with mean ± SD values for dry bulb temperature and relative humidity being 21.9 ± 3.4°C and 56.7 ± 9.5%, respectively (Figure 1).
Before starting the RST and immediately upon completion, a capillary blood sample (125 μL) was taken from the earlobe of participants using glass capillary tubes (D957G-70-125 Clinitubes; Radiometer, Copenhagen, Denmark) to assess blood lactate concentration (HLa−) and pH. After each set of repeated sprints, a smaller capillary blood sample (35 μL; due to time constraints) was taken from the earlobe of participants using similar tubes (D957G-70-35 Clinitubes, Radiometer) for HLa− measurement. Samples were transported (on ice) back to the laboratory where they were analyzed using a blood-gas analyzer/radiometer (ABL 625, Radiometer).
After presupplementation testing, participants were matched in 4 groups, based upon sport played (Australian football, soccer, or hockey) and current competition level. Participants were then randomly assigned to the BA only, sodium bicarbonate only (NaHCO3), BA plus sodium bicarbonate (BA/NaHCO3), or placebo only (placebo) group. Beta alanine (Carnosyn slow release; Collegiate Sport Nutrition, San Marcos, CA, USA) was administered orally for 28 days with a dose of 80 mg·kg−1·BM·day−1 (∼6 g·day−1) taken as 4 split doses over each day, whereas the glucose placebo (10 g·day−1; Glucodin, Valeant Pharmaceuticals Australasia, Rhodes, New South Wales, Australia) was taken in a similar fashion to mimic the BA supplementation as closely as possible. Sodium bicarbonate (0.3 g·kg−1 BM, Sodibic, Aspen Pharmacare Australia Pty Ltd, St. Leonards, New South Wales, Australia) or placebo (sodium chloride, matched for osmotic pressure; 0.208 g·kg−1 BM) was taken as an acute dose 1 hour before the postsupplementation exercise trials by all groups. This procedure ensured that all groups took either an active or placebo dose before the postsupplementation testing (i.e., BA = serial BA + acute placebo, NaHCO3 = serial placebo + acute sodium bicarbonate, BA/NaHCO3 = serial BA + acute sodium bicarbonate, placebo = serial placebo + acute placebo). All doses were administered in opaque gelatin capsules to blind participants. Before the study, pilot testing for 2 weeks on n = 6 volunteers using this daily dose of BA was well tolerated, with no side effects being reported. Further, an acute dose of 0.3 g·kg−1BM of sodium bicarbonate was selected because it has been shown to be well tolerated, with minimal side effects reported by participants (2,11,29,31). Athletes were visited weekly to distribute supplements, discuss dose compliance and to check on health during the study. They also completed a food diary for the 2 days prior to each RST to ensure that a similar diet (total energy and protein) was consumed prior to each test, with no differences identified between pre-supplementation and postsupplementation values in each group (average total daily energy intake 8600–9900 kJ, p = 0.07–0.34; protein 111–133 g, p = 0.15–0.71). Following 28 days of supplementation, participants returned for postsupplementation testing, which was conducted in an identical manner to presupplementation testing.
Performance measures recorded included TST for all 3 sets for the RST; TST for the 6 sprints in each set (set1, set2, set3); first 20 m sprint time and best 20 m sprint time for each set. Further, percentage decrement scores over the 6 sprints in each set were calculated using the method described by Fitzsimmons et al. (18). Exercise performance, HLa−, and pH results for the duplicate presupplementation and postsupplementation RST trials were combined and averaged for each group (BA, NaHCO3, BA/NaHCO3, and placebo), so that 1 presupplementation and 1 postsupplementation mean value was obtained for each variable.
Given the small changes in performance that were expected from the running sprint data, the data was interpreted using Cohen's d effect sizes and thresholds (<0.49, small; 0.5–0.79, moderate; ≥0.8, strong). Further analysis was conducted to identify the smallest worthwhile change (clinically beneficial effect) in performance scores between the BA, sodium bicarbonate, BA/sodium bicarbonate, and placebo trials using the method (and spreadsheet) described by Hopkins (23). Each participant's change score was computed as a percent of the presupplementation value and log transformed to reduce any bias from nonuniformity of error. A smallest worthwhile change of 0.8% was employed to determine the chance that differences were practically significant during the 4 treatment trials (30). Where the chance of benefit or harm was calculated to be >5%, the true effect was deemed unclear (23). When clear interpretation was able to be made, a qualitative descriptor was assigned to the following quantitative chances of benefit: 25–75%, benefit possible; 75–95%, benefit likely; 95–99%, benefit very likely; >99%, benefit almost certain (8).
Total Sprint Times
The effects of each supplement on the TST and sets 1, 2, 3 are presented in Table 2. Postsupplementation TST was on an average, 1.28 seconds faster (compared with presupplementation) after sodium bicarbonate only, with this supported by a “very likely” chance of benefit. Further, the combination of sodium bicarbonate and BA resulted in a “possible” benefit (mean 0.58 seconds faster), with all other group results being trivial with low effect sizes.
Similar results were found for the individual sets, with moderate effect sizes (sets 2 and 3) and “likely” to “very likely” benefits (all sets) found for the sodium bicarbonate group only, whereas the combination of BA and sodium bicarbonate resulted in “likely” benefits for sets 2 and 3.
Mean 20 m Sprint Times for Each Set
Results for mean individual sprint times (postsupplementation vs. presupplementation) for set 1 found that sodium bicarbonate alone resulted in “likely” to “very likely” benefits in performance for sprints 3–6, with sprint 5 supported by a moderate ES (d = 0.56, Figure 2). Further, “very likely” to “almost certain” benefits were found for sprints 7–12 in set 2 after sodium bicarbonate supplementation; with sprints 8–10 and 12 also supported by moderate ES (d = 0.56–0.63). Also in set 2, combined BA and sodium bicarbonate resulted in “likely” benefits for sprints 7–10 and 12, whereas BA alone resulted in “likely” benefits for sprints 10 and 11. This pattern continued in set 3, with “possible” to “almost certain” benefits found for sprints 13–18 (moderate ES for sprints 13–17; d = 0.53–0.73) after sodium bicarbonate supplementation, whereas combined BA and sodium bicarbonate resulted in “possible” to “very likely” chances of benefit in these same sprints. Finally, BA alone resulted in a “likely” benefit for sprint 18 only.
First and Best 20 m Sprint Times and Percentage Decrement
The results for first and best sprint times for each set are shown in Table 3. First sprint times (postsupplementation vs. presupplementation) improved most after sodium bicarbonate in sets 2 and 3 (mean, 0.06, and 0.11 seconds faster, respectively), with these results supported by “very likely” chances of benefit, and moderate ES (set 3). Combined BA and sodium bicarbonate also resulted in a “likely benefit” to first sprint performance in sets 2 and 3 (0.05 and 0.04 seconds faster, respectively), but the BA and placebo groups did not record any meaningful differences.
Similarly, best sprint times improved most after sodium bicarbonate supplementation in sets 2 and 3 (0.06 and 0.09 seconds faster, respectively), with these results supported by “very likely” chances of benefit and moderate ES (set 3). The combination of BA and sodium bicarbonate also resulted in “likely” benefit to best sprint times in sets 2 and 3.
Percentage decrement values (postsupplementation vs. presupplementation) were lower after sodium bicarbonate supplementation for set 1 (large ES: d = 0.81 and “likely” benefit) and set 2 (“ikely” benefit). The placebo group recorded a higher value after supplementation for set 1 (moderate ES: d = 0.52 and “likely” detrimental), but no meaningful differences were noted for either the BA or combination groups.
Blood Lactate and pH
These results are displayed in Figures 3 and 4 (HLa−) (pH). Blood lactate concentrations increased preexercise to postexercise in all trials, with differences between after supplementation and before supplementation values being higher in the sodium bicarbonate and combined BA and sodium bicarbonate groups after sets 1–3, with these values supported by moderate to large ES (d = 0.59–0.60, d = 0.80–0.97, and d = 0.66–0.86, respectively). After supplementation, results were similar to before supplementation for both the BA and the placebo groups.
Blood pH decreased preexercise to postexercise in all trials, but postsupplementation values were higher at preexercise for the sodium bicarbonate and combined BA and sodium bicarbonate groups, with these results supported by moderate to large ES (range for d = 1.11–1.39). Blood pH was lower at preexercise for the BA and placebo groups, with these results supported by moderate to large ES (d = 0.51–1.18). After supplementation, postexercise values were higher than before supplementation in the sodium bicarbonate and combined BA and sodium bicarbonate groups (d = 0.51 and 0.80, respectively). Conversely, blood pH values postexercise before and after supplementation were similar for the beta BA and placebo groups.
This is the first study to assess the effect of combined BA and sodium bicarbonate supplementation on a RST that typified the duration of (and time between) sprints commonly performed in team sports. Sodium bicarbonate supplementation (alone) resulted in the best repeated-sprint performance, with some improvement also seen (but to a lesser extent) when a combination of BA and sodium bicarbonate was used. This outcome was surprising as it was hypothesized that combining supplementation of sodium bicarbonate (extracellular blood buffer) and BA (intracellular muscle buffer via carnosine) would result in enhanced repeated-sprint performance beyond what is possible with either supplement alone.
Improvement in RSA performance after sodium bicarbonate supplementation alone has previously been demonstrated in several studies (10,11,28,31). Specifically, Bishop et al. (11) reported that a similar dose of sodium bicarbonate to that used here, ingested 90 minutes before completing a single set RST (5 × 6 seconds cycle sprints departing every 30 seconds), increased total work and peak power when compared with a placebo. Further, Bishop and Claudius (10) reported significant improvements in work done and peak power in several sprints during the second half of a prolonged RST (2 × 36 minute halves, ∼2 minutes blocks of 4 second sprint, 100 seconds active recovery, 20 seconds rest with 2 extra 5 × 2 seconds repeat sprint bouts during each half). It is likely that the performance improvements seen in the current study were the result of the alkalosis induced (as a result of ingesting NaHCO3) before the RST, with this higher pH maintained throughout the duration of the RST (Figure 4). This is in agreement with the proposed ergogenic mechanism of sodium bicarbonate (10–12).
A smaller performance benefit from combined supplementation of BA and sodium bicarbonate was also seen here. This result was somewhat unexpected, as it had been previously reported that the combination of BA and sodium bicarbonate improved exercise performance beyond what was possible with either supplement in isolation (9,35). For example, Bellinger et al. (9) reported that average power output (3.1%) and total work done (3.0%) were improved during a 4-minute cycling time trial after supplementation with sodium bicarbonate. Adding BA supplementation then resulted in a further improvement (albeit, NS) of 0.2% to average power and total work done, with the researchers noting improvement in 6 of 7 participants. Similarly, Sale et al. (35) reported that ingesting sodium bicarbonate after BA supplementation resulted in a further improvement in time to exhaustion of ∼6 seconds (4.1%; NS) in participants completing 2–3 minutes supramaximal cycle capacity test. As BA has been associated with benefit in exercise performance in efforts lasting 60–240 seconds (21), it is possible that the shorter sprints used in the current study were not long enough to utilize the full potential ergogenic effects of BA supplementation. Our results suggest that BA supplementation, either alone, or in combination with sodium bicarbonate, may have a limited ergogenic effect in repeated short sprint bouts.
Further, when BA and sodium bicarbonate supplementation were combined, repeated-sprint performance was not increased by the same magnitude as sodium bicarbonate supplementation in isolation. It has been reported that the acute ingestion of a stock rich in carnosine and anserine (1.5 g) reduced the contribution of the bicarbonate buffering system during a bout of repeated sprints (10 × 5 second cycle sprints separated by 25 seconds rest; Suzuki et al. ). However, the largest buffering effect of carnosine taken orally would be in the blood (if at all, due to rapid absorption and hydrolysation in the plasma); therefore, the conclusions of this study might be questioned and require further research to confirm. Conversely, Baguet et al. (4) reported that several weeks of supplementation with BA attenuated the fall in intracellular pH during 6 minutes of high-intensity cycling. These authors noted that circulating bicarbonate and HLa− concentrations were unchanged during exercise and concluded that BA supplementation did not affect the function of the blood bicarbonate buffering system. Therefore, the reason why the combination of supplements used here was not as beneficial to performance as sodium bicarbonate alone remains undetermined. More research is needed to investigate the effects of combining supplements such as sodium bicarbonate and BA supplementation together to attempt to alter both blood and muscle buffering systems simultaneously.
Interestingly, our results also found that BA supplementation alone only marginally improved RSA (sprints 10, 11, and 18). Hoffman et al. (22) have reported a trend for a slower fatigue rate in American football players completing a repeated line drill. However, a lack of benefit of BA supplementation on RSA has been found in other studies (36,43). Importantly, although Saunders et al. (36) reported no significant improvements in RSA after supplementation with a similar dose of BA to that used in the current study (4 weeks, 6.4 g·day−1), they observed little deterioration in sprint times during the test before supplementation, and relatively low HLa− values posttest (3–6 mmol·L−1). In the current study, percentage decrement values were 3–5% for each set (typical of this test; Sim et al. ), although the HLa− response was higher (6–8 mmol·L−1). This may have allowed the buffering effects of carnosine to work more effectively, which may explain the small degree of improvement found in the later sprints of sets 2 and 3 here. Sweeney et al. (43) also reported no significant improvements in performance of participants (some team sport, some healthy males) completing 2 sets of 5 × 5 seconds sprints (45 seconds rest between sprints, 2 minutes between sets). However, the longer rest periods used in their study, compared with the current one, may have allowed participants to recover enough to have limited any ergogenic effect by the time the next sprint commenced.
The limitations of this study include a small sample size within each group that could potentially limit the meaningfulness of the results. Further research using a larger sample size should be conducted to confirm/refute these findings. In addition, as no measurements of intramuscular carnosine were possible here, the relationship between changes in these concentrations, potential interactions with acute sodium bicarbonate loading, and repeat sprint exercise performance is necessary to support our findings. In conclusion, supplementing with sodium bicarbonate alone resulted in better RSA, where the repeated sprints are of similar duration (and time between) to those found in team sports, than BA and sodium bicarbonate supplementation in combination or BA alone. This information is pertinent to team-sport players and coaches.
Supplementing with an acute dose of sodium bicarbonate (0.3 g·kg−1BM, 60–90 minutes before exercise) may be effective for improving repeated-sprint performance during team-sport match play (e.g., Australian football, soccer, and hockey). Supplementation with BA may not be ergogenic for these sports, which require repeated short (∼2–4 seconds) sprints with brief (∼15–30 seconds) recovery periods. Further, combining both supplements is not recommended, as this combination may result in a lower magnitude of performance improvements than sodium bicarbonate supplementation in isolation.
The authors thank Professor Louise Burke (Australian Institute of Sport) for her invaluable assistance in sourcing and obtaining the BA used in this study. The results of the present study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association.
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