The aim of this study was to determine the effect of 5 weeks of BA supplementation on performance during repeated brief all-out sprints. Results indicate that 6 g per day of BA supplementation had no effect on HP or performance decrement (% fatigue) during repeated sprints. The decrease in HPmean from pre to posttesting in both groups may be attributed to a change in pacing strategy during the sprint. We observed that both groups produced a nonsignificant increase in HPpeak after supplementation, which may have led to earlier fatigue within each sprint, resulting in a lower HPmean. The BA group increased HPpeak 2.4%, whereas HPmean decreased 1.0%. Similarly, the C group increased HPpeak 1.9%, which was accompanied by a 0.9% decrease in HPmean. Although the small decrease in HPmean produced a significant main effect by time, it is unlikely that this decrease is practically significant for most field sport athletes. The lack of a group × time interaction indicates there was no difference in the improvement in HPmean due to BA supplementation.
One of the key outcomes of a repeat sprint protocol is the measure of performance decrement over the number of sprints. In this study, we looked at the power decrease over ten 5-second sprints with a 45-second recovery. To be able to conclude that BA provides some positive ergogenic properties, supplementation with BA should improve the performance decrement (smaller decrease in power) for both HPpeak and HPmean. Our results show that BA did not improve the performance decrement; however, the results should be interpreted with caution. As shown in Figure 3, the individual pre- to post-supplementation % fatigue responses for both BA and C groups are quite variable. Although the method used to determine performance decrement in this study has been evaluated and compared with other methods for reliability and validity and determined to be the most reliable and valid method, it has also been shown to have a test-retest variability in fatigue of about 30% (13).
The absence of an ergogenic effect may be related to the inability to increase muscle carnosine levels by the dosing strategy used in this study. Beta-alanine is likely the rate-limiting substrate and essential supplement required to increase carnosine levels within the muscle tissue (2). Previous research has demonstrated that BA supplementation can increase muscle carnosine levels and contribute to the acid-base buffering capacity of the muscle (8,12,14,15,18). For example, Harris et al. (16) found a 42% increase in carnosine levels after supplementing with 3.2 g per day of BA and a 64% increase with 6.4 g per day after 4 weeks of supplementation.
Although previous research has shown an improvement in performance after BA supplementation (9,17,18,29), it might be concluded from those studies that the ergogenic benefit may be more related to the dominant energy system used during the performance and as a result depend on the duration of the maximal effort. For example, Hill et al. (18) demonstrated a 16% increase in total work performed at 110% of maximum cycling power to exhaustion (∼150 seconds) after BA supplementation for 4 weeks. In addition, Derave et al. (9) demonstrated that BA improved performance of intermittent exercise bouts of isokinetic leg extensions (5 bouts of 30 maximal repetitions with 1-minute rest between bouts) where each bout lasted approximately 45 seconds. The ergogenic benefits however were not noticed until the last 2 sets of the intermittent protocol. Stout et al. (29) demonstrated an increase in neuromuscular fatigue threshold using an incremental cycling challenge that used four to five 2-minute stages after BA supplementation of 1.6 g per day for 28 days. Although many previous studies support the use of BA supplementation as a performance-enhancing ergogenic aid for some types of anaerobic exercise, this is the first study to investigate the effects of BA supplementation on repeat sprint exercise performance.
Our findings of the inability of BA supplementation to maintain HP during repeat sprint exercise in the present study are consistent with other studies using all-out efforts for less than 1 minute (9,19). For example, Hoffman et al. (19) found no additional benefit of supplementing with BA along with creatine compared with creatine alone when performing two 30-second Wingate tests separated by 3 minutes of active recovery. In the same study (19), the supplementation of BA did not improve the maintenance of jumping power during a 20 consecutive jump test. In addition, after 4 weeks of 4.8 g per day of BA (which significantly increased intramuscular carnosine), Derave et al. (9) found no change in performance time (average ∼52 seconds) in a single 400-m sprint in trained sprinters.
These findings, along with the results of our study, suggest that factors other than changes in pH may be more important than the accumulation of H+ ions for producing fatigue during repeated brief sprints with short recovery periods. During a single bout (6 seconds) of high-intensity exercise, use of PCr and fast glycolysis each account for approximately half of the total energy needed; however, during repeated sprints, a greater depletion of PCr is observed than during a single maximal effort (9). The rate of PCr resynthesis is influenced by the metabolic environment of the muscle, H+ ion concentrations of the muscle and blood, and ATP concentration within the muscle (27). It has been demonstrated that short recovery periods (30-180 seconds) may not provide adequate time to restore PCr values to resting levels, thus leading to an increased need for additional energy from fast glycolysis (2,9). Indeed, Bogdanis et al. (6) reported that the halftime for PCr resynthesis was 57 seconds, considerably longer than the recovery period (45 seconds) used in the present study. The incomplete resynthesis of PCr may explain the relatively high levels of blood lactate observed in our study but also suggest that changes in pH may not be the sole explanation for muscle fatigue during our sprint protocol. The availability of PCr may be the limiting factor in multiple sprint performance (4,5,9). During repeated sprints, PCr may only be partially restored if the recovery bouts are less than 1-2 minutes long and may take more than 6 minutes to fully recover (4,9). It is likely that the 45-second recovery periods used in our study did not allow for sufficient PCr resynthesis to maintain a considerable contribution to power output beyond the first couple of sprints. Therefore, BA supplementation may not have a large effect on repeated sprint performance because the lack of PCr resynthesis may have a greater effect on fatigue and decrease in performance than the accumulation of H+. In support of this notion, Bishop et al. (3) found that the physiochemical buffering in the muscle during a 5 × 6-second sprint protocol with 24-second recovery had no relationship to repeated sprint ability. They suggest that the contribution from the metabolic reactions that consume H+, the sarcolemmal lactate/H+, and Na+/H+ exchange mechanisms; capillarization; muscle blood flow; and changes in the intracellular strong ion difference may be a greater influence than the physiochemical buffering in the muscle. They also suggest that the individuals with the best repeated sprint ability are likely the ones who produce fewer H+, especially in the first few sprints (3).
In conclusion, it was determined that BA supplementation does not have an ergogenic effect on repeated brief sprints. The lack of PCr resynthesis associated with short recovery periods may more likely explain the limiting factors for performance.
The ability to produce and maintain bouts of high-power output during periods of multiple sprint work is important to many field-based sports. Previous research using repeat high-intensity sprint performance has attributed fatigue to the availability and resynthesis of PCr. Phosphocreatine depletion may be a greater cause of fatigue in this protocol than acidosis, and as a result, any effects of BA were not noticeable. Although this area requires more investigation, the results of this study suggest that sports such as football, soccer, lacrosse, and others with repeated sprint efforts should probably not rely on BA supplementation for performance enhancement.
The authors would like to thank the University of Wisconsin-La Crosse Graduate Research Grant Program for assisting with funding for this project. The authors would also like to acknowledge Athletes Edge Nutrition, Miami, FL, for their help in providing supplementation. The results of the present study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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