The use of sodium bicarbonate (NaHCO3) as an alkalizing agent to enhance blood buffering capacity has been ongoing for decades (13,16,19). It has been proposed that supplementing exogenous bicarbonate provides an electrochemical gradient between the intra- and extracellular milieu, thus allowing for greater facilitation of proton (H+) removal during intense exercise (12,13). Excessive accumulation of H+ during such an activity is thought to inhibit contractile protein cross-bridging, sarcoplasmic reticulum function, and glycolytic flux within skeletal muscle (11,14,29). Current application and practice of NaHCO3 loading has been recently reviewed (19), yet definitive recommendations as to the degree of efficacy remain equivocal. In brief, it appears that any observed performance benefit from NaHCO3 loading is dependent upon the timing of ingestion, the participant's individual dose response, and the associated exercise requirement (16,19). If a consistency throughout the scientific literature may be drawn however, it is that exercise demanding either a prolonged high-intensity effort (e.g., >100% peak power output for a minimum of 2 minutes) (18,17) or one that consists of multiple high-intensity bouts separated by minimal recovery time (4,5) can potentially benefit from a pre-exercise alkalotic state.
One sport that may be categorized within the multiple repeated high-intensity exercise domain is that of boxing. Typically, a modern day boxing match will consist of a predetermined number of rounds, each lasting 3 minutes while separated by a 1-minute seated recovery (World Boxing Association). Although one may assume that the physical demands of such an activity would be high, there has been little scientific documentation in regard to metabolic rate or cardiovascular stress during a boxing event (3,7). Alternatively, most research has focused on the catastrophic outcomes of the sport, with a preponderance of literature available regarding both acute and chronic brain trauma (10,15,24). Nonetheless, the physiological demands of the sport of boxing would appear to emulate other sports (i.e., judo or mixed martial arts [MMA]) in which scientific literature is available, albeit limited (1,8,26). For example, after two 4-minute sparring rounds of MMA separated by a 1-minute recovery, Amtmann et al. (1) reported average lactate values of 15.2 ± 4.8 mmol·L−1 and rates of perceived exertions (RPEs) in the range of 13-19. In addition, Guidetti et al. (9) have shown a high individual anaerobic threshold to correlate well with middleweight boxing performance (as assessed by the International Amateur Boxing Association). As such, it could be assumed that there is a high rate of glycolytic flux responsible for sustaining the adenosine triphosphate resynthesis required for such an activity (28). Therefore, providing an enhanced extracellular proton (H+) buffering medium by NaHCO3 loading may either (a) aid in the homeostatic maintenance of glycolysis for longer periods (or progressively longer throughout a boxing match) (29) or (b) sustain Ca2+ release and resequestering in the sarcoplasmic reticulum through increasing the strong ion difference (SID) (12). Providing such a benefit may ultimately delay skeletal muscle fatigue, indirectly aiding in a boxer's overall performance (11,25).
To our knowledge, the use of NaHCO3 supplementation during boxing has not been reported in the scientific literature. Therefore, it was the intention of this study to observe the ergogenic potential of NaHCO3 ingestion on boxing performance. For the purposes of this study, boxing performance was defined in terms of (a) physiologic responses (e.g., heart rate [HR] and acid-base balance), (b) subjective exertion scales (RPE), and (c) objectively assessing successful punches thrown and landed (punch efficacy). We hypothesized that NaHCO3 loading would provide an enhanced buffering medium during the boxing match and have a positive effect on punch efficacy.
Experimental Approach to the Problem
The repeated measures design consisted of 2 competitive sparring bouts separated by 1 week. The boxers were paired according to current weight and boxing ability (as defined by UK amateur rankings) and instructed to replicate their normal prefight routine for both sparring bouts. Study validity and reliability were maintained within respectable limits for the applied nature of the study. The dependent variables selected in this study (blood acid-base status, electrolytes, HR, RPE, and punch efficacy) are all commonly used to evaluate intermittent high-intensity performance. Every attempt was made to control for potentially confounding variables (e.g., previous strenuous exercise, diet, and hydration) that were identified during pilot work. All participants arrived at the boxing gymnasium at a prearranged time in pairs 1½ hours prior to the bout for collection of pre-exercise blood acid-base balance and to consume either 0.3 g·kg−1 body weight (BW) of NaHCO3 (BICARB) or 0.045 g·kg−1 BW of NaCl placebo (PLAC) mixed in diluted low calorie-flavored cordial (500 ml). The sparring bouts consisted of four 3-minute rounds, each separated by 1-minute seated recovery. The sparring was monitored and refereed by an experienced member of the club's coaching staff (licensed as a “full coach” by the Amateur Boxing Association of England [ABAE]).
A total of 10 (177.8 ± 8.1 cm, 73.1 ± 10.0 kg, 22 ± 3 years) participants volunteered to partake in the study from a local amateur boxing club (St Pauls Amateur Boxing Club, Hull, UK). The boxers were considered of high standard (e.g., representing country at national and international tournaments [Olympic competition]). The boxers had an average of 7 ± 4 years boxing experience and were all currently in precompetition training phases for upcoming bouts. All participants were informed both verbally and in writing of the experimental risks associated with their involvement in the study. Subsequently, all participants provided written informed consent in accordance with the departmental and university ethical procedures and following the principles outlined in the Declaration of Helsinki.
Upon arrival at the gymnasium and after 10-minute seated rest, preingestion blood samples were obtained. The boxers were then allowed 15 minutes to consume their prescribed drink (randomized [counter-balanced] double-blinded BICARB or PLAC) and thereafter sat quietly for 1 hour. After the loading sequence was completed, the boxers were suited for the match (gloves [14 oz sparring], headgear, mouthpiece and HR monitor [Polar Team Systems, Polar USA, Long Island, NY]) and allowed 3 minutes of shadow boxing in the ring for warm-up (this routine was administered simultaneously for both boxers by the same coach). Thereafter, final instructions were given and the sparring commenced. Throughout each round, 2 cameras (SONY DCR-SR190E HDD camcorder; Sony UK Ltd., Surrey, UK) were placed at different elevated locations to record the bouts and for subsequent punch count analysis. Successful punches landed (punch efficacy) were determined for each round independently by 2 different ABAE-licensed coaches. Timing of the rounds was kept by an independent observer using a standard stopwatch. At the end of each round, both boxers were independently asked to rate their perceived exertion (Borg scale 6-20). Upon completion of the 4 rounds, the boxers immediately removed their gloves for a final postsparring capillary blood sample. The trial procedure was then replicated the following week, with the exception of the boxers consuming the opposite drink (BICARB or PLAC).
Blood Acid-Base Analyses
All blood samples were obtained aseptically via capillary finger sticks. In order to analyze blood pH, HCO3−, and base excess (BE), whole blood was collected in a balanced heparin 200 μL blood gas capillary tube. The sample was immediately analyzed for blood gas concentrations and acid-base balance using a clinical blood gas analyzer (ABL77 Blood gas and electrolyte analyzer [Radiometer Ltd., Crawley, West Sussex, UK]). In addition, whole blood concentrations of Na+, K+, and Cl− were also analyzed for the presparring and postmatch conditions. Whole blood lactate samples were collected in Microvette CB300 tubes (300 μl capacity) containing lithium heparin and fluoride. Samples were immediately analyzed using a Lactate Pro Lactate Analyzer (Arkray Inc., Kyoto, Japan).
Data are presented as mean ± SD. Prior to analysis, all data were assessed for normal distribution, homogeneity of variance, and independence of errors. Sample size (n = 10) was determined from a power analysis using the dependent variable with the highest variability as determined by SDs from past research (6). All blood measures were done in duplicate, and the range of intraclass correlation coefficients were 0.85-0.97, p ≤ 0.01 for all dependent variables, respectively. Blood acid-base (pH, HCO3−, and BE), strong ions (Na+, K+, and Cl−), HR (HRave and HRmax), and RPE profiles were analyzed using 2-way (condition × time) analysis of variance (ANOVA) for repeated measures. The differences between conditions for punch efficacy were analyzed using a 1-sample t test. The punch efficacy data were markedly skewed, which was corrected with a natural log transformation. One-way ANOVA for repeated measures was used to analyze differences in baseline values (preingestion) between conditions for acid-base balance. Post hoc analysis was conducted using Tukey's Honestly Significant Differences (HSD). Two-tailed significance was accepted at p ≤ 0.05. Statistical analyses were completed using Statistica Software v.6 (StatSoft, Inc., Tulsa, OK) and GraphPad Prism 4.0 (GraphPad Software, Inc., San Diego, CA).
Blood Acid-Base Response
Mean (SD) blood acid-base data are presented in Table 1. No significant differences existed between conditions for baseline values of pH (F = 3.2; p = 0.11), HCO3− (F = 0.03; p = 0.87), and BE (F = 0.25; p = 0.63). During the trial period, there were significant main effects for condition on pH (F = 18.5; p < 0.003), HCO3− (F = 32.1; p < 0.001), and BE (F = 32.4; p < 0.001). The PLAC condition resulted in significantly lower buffering potential compared with the BICARB condition for all 3 variables (p ≤ 0.01). There were significant main effects of time on pH (F = 71.6; p < 0.001), HCO3− (F = 171.3; p < 0.001), and BE (F = 178.6; p < 0.001). All 3 variables were significantly higher postingestion than at the end of sparring (p < 0.001). There were also significant condition × time interaction effects for HCO3− (F = 23.7; p ≤ 0.001; Figure 1) and BE (F = 27.0; p < 0.001), but not for pH (F = 0.54; p = 0.48) (post hoc differences are depicted in Table 1).
Strong Ion Difference
During the trial period, there was no significant condition × time interaction for Na+ (F = 0.44; p = 0.53); however, there was a main effect for time (F = 18.0; p < 0.01) (post hoc differences are depicted in Table 2). There were significant condition × time interaction effects for K+ (F = 7.9; p < 0.05), with post hoc analysis revealing differences between PLAC and BICARB for presparring (p < 0.01) (Table 2). There was also a significant condition × time interaction effect for Cl− (F = 8.3; p < 0.05), with post hoc analysis revealing differences between PLAC and BICARB for both presparring (p < 0.001) and postmatch (p < 0.001) (Table 2).
Mean (SD) HR, RPE, and punch efficacy data are presented in Table 3. The differences between conditions for total punch efficacy was significant (t = 13.0; p < 0.001). There were no significant main effects for condition for HRave (F = 1.2; p = 0.32) or HRmax (F = 0.16; p = 0.70). Conversely, there were significant main effects of time on HRave (F = 24.9; p < 0.001) and HRmax (F = 38.1; p < 0.001). There was a continual increase in both HRave and HRmax from rounds 1 through 4 (p < 0.05). There was no significant condition × time interaction effects for HRave (F = 2.0; p = 0.15) or HRmax (F = 1.2; p = 0.32). There were no significant main effects of condition on RPE (F = 1.5; p = 0.26). Conversely, there was a significant main effect of time on RPE (F = 60.0; p < 0.001). Similar to HRave and HRmax, RPE continued to increase from rounds 1 through 4 (p < 0.05). However, there was no significant condition × time interaction effects for RPE (F = 1.1; p = 0.38).
This study observed the potential for improved boxing performance after the ingestion of a standard 0.3 g·kg−1 load of sodium bicarbonate. As hypothesized, NaHCO3 ingestion resulted in an elevated blood buffering status prior to the boxing match, with that elevation being sustained throughout the 4 rounds of boxing (Figure 1). Of more practical importance, however, was the improvement observed in punch efficacy during the BICARB condition.
Numerous studies have reported an ergogenic benefit of NaHCO3 supplementation during multiple bouts of high-intensity exercise (4,21,30). Presumably, this is due to an increased extracellular concentration of HCO3− caused by the exogenous NaHCO3 load. As HCO3− permeability across the cellular membrane is thought to be either nonexistent or very limited (31), the HCO3− concentration remains disproportionately higher in the extracellular medium. Pre-exercise elevated blood buffering potential is commonly reported throughout the NaHCO3 literature (19), with a standard dose of 0.3 g·kg−1 tending to increase pre-exercise HCO3− and BE values by approximately 5-7 mmol·L−1 and 5-6 mEq·L−1 (19), respectively. The actual ergogenic mechanism responsible for providing a performance enhancement is still widely debated. It appears to be that either (a) the existing electrochemical gradient provides an enhanced H+ facilitation out of the working muscle (presumably through the lactate/H+ cotransport system) and ultimately glycolytic flux is maintained for longer periods (22,23) or (b) the influence of an SID on the physiochemical properties of both intra- and extracellular milieu that is responsible for maintaining skeletal muscle contraction (e.g., Ca2+ resequestering within the sarcoplasmic reticulum) (14). The influence of either mechanism (or in combination) would potentially benefit the cellular mechanisms associated with resisting fatigue (e.g., contractile function or phosphocreatine resynthesis).
In the current study, the presparring blood buffering potential of the boxers was elevated and comparable to other reports employing the same loading strategy (19). Similar ionic shifts were also evident in the extracellular fluid, as K+ and Cl− were significantly lower after ingestion (Table 2). This observation has been linked with an increased SID, which purportedly may aid in the maintenance of action potential velocity and ultimately affect Ca2+ release in skeletal muscle (27). The boxers also reported only experiencing minor adverse effects (e.g., gastrointestinal [GI] discomfort); however, these had completely subsided prior to the sparring event. We believe that this positive response to the NaHCO3 ingestion was influenced by the loading strategy employed, suggesting that the boxers were in an optimal state for competition.
It was originally hypothesized that due to the high-intensity intermittent nature of boxing, an enhanced blood buffering capacity would benefit the boxer's performance. The physiological profile during the competition would suggest that regardless of condition, the work rate of the boxers progressively increased throughout the 4 rounds (Table 3). This incremental progression would indicate that the boxers were employing some form of self-pacing strategy (feeling out the opponent) inherent to the nature of the competition (20). Although drawing definitive conclusions under these conditions is difficult, we felt that by intervening between rounds, we would have decreased the ecological validity of our findings. As such, we have included the cardiovascular and subjective exertion data as we are unaware of any peer-reviewed normative data in the literature profiling the cardiovascular strain associated with boxing (Table 3).
In terms of practical application and importance, however, the NaHCO3 loading may have been responsible for the observed increase in total punch efficacy (p < 0.001). This finding is important, in particular when considering the elite level performer (regardless of weight class) and the finite margins separating these individuals. If an enhanced blood buffering during recovery between rounds is evident and there are no indications of performance decrement caused by the supplement, then NaHCO3 loading (0.3 g·kg−1 approximately 1-2 hours prior to the bout) should be considered potentially ergogenic for the sport of boxing. Any performance advantage that is evident after only 4 rounds may also become more profound during an event lasting 12 or 15.
This notion would also be supported in light of recent published reports of NaHCO3 ingestion enhancing performance during more endurance based high-intensity activity (4,21,30). The only study we were able to locate that used a similar study design to the current was that of Artioli et al. (2). These authors used 3 bouts of a specific judo test followed by four 30-second upper body Wingate tests to assess the ergogenic potential of a NaHCO3 load (2). During the 3 sport-specific bouts, the athletes performed a significantly greater number of throws during the second (27.0-25.9) and third (27.0-25.6) bouts, compiling an overall average increase in throws of 5.1% during the BICARB trials (2). This overall increase in percentage (5.1%) is similar to the increased number of successful punches landed observed in the current study (5%), again suggesting a potential performance improvement and supporting the practice of loading with 0.3 g·kg−1 of NaHCO3. The 2 studies also illustrate performance improvements in 2 distinctly different environments (Artioli et al. measured throws in a controlled environment where the current study employed a “live” event). Interestingly, the subjective data (RPE) reported in the study of Artioli was similar again to that in the current (ranging from 13 progressing to 18) and irrespective of the intervention (NaHCO3 or placebo). This lack of subjective perception of increased effort has also been reported in other NaHCO3 studies (32). Although it appears that NaHCO3 loading does not impact the psychological perception of intense exercise, we still advocate a trial period prior to loading before a competition. This will provide those involved (coaches, trainers, etc.) with each boxer's degree of GI tolerance to the load and also allow for alternative loading strategies to be implemented (19).
In conclusion, the present study assessed the ergogenic potential of NaHCO3 loading prior to a boxing competition. The findings suggest that a standard loading dose (0.3 g·kg−1) enhances the blood buffering potential and may positively influence the performance outcome in terms of punch efficacy. This study was also the first to report normative physiologic and subjective data during a boxing competition. Future study in this area with specific regard to longer boxing matches (e.g., 12-15 rounds) and to the potential response to training under a NaHCO3-loaded condition will help further clarify whether this practice is advantageous toward the sport.
The authors would like to thank all those associated with St. Pauls Amateur Boxing Club in Hull for their cooperation and the use of the training facility. The authors have no undisclosed professional relationships with companies or manufacturers that would benefit from the results of the present study. 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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Keywords:© 2010 National Strength and Conditioning Association
metabolic alkalosis; punch efficacy; buffering capacity