Because more adults are participating in collegiate and professional athletics than 2 decades ago, athletes are constantly looking for a competitive advantage to further increase exercise performance (21). This includes, but is not limited to, altering energy or carbohydrate intake, environmental training (e.g., live-high-train low, heat training), and using ergogenic aids. These methods have shown to increase performance in various exercise settings. However, the use of ergogenic aids is the most common method to increase exercise performance, because >60% of athletes worldwide use some form of ergogenic aid (31).
Creatine monohydrate and sodium bicarbonate supplements are 2 widely studied ergogenic aids that potentially delay fatigue and increase performance, in particular during high-intensity, intermittent exercise (1–11,16,18–28,32,37,40). During high-intensity exercise, potential contributors to fatigue can be related to muscle energy production, a decline in muscle adenosine triphosphate (ATP), or impaired electrochemical events of muscle contraction-relaxation production (29). These decrements in performance can also be related to the accumulation of metabolites during exercise such as hydrogen ions resulting from increased lactic acid formation in high-intensity exercise (29). Previous studies have shown that short-term supplementation of creatine increases exercise performance by increasing ATP resynthesis (2–3,11–14,40). Additionally, short-term supplementation of sodium bicarbonate increases hydrogen ion buffering capacity, thereby delaying fatigue and increasing exercise performance (4,5,7,19,22–28,36).
Although many studies have addressed the independent effects of creatine monohydrate and sodium bicarbonate on performance, to our knowledge, only one published study has examined the combined effect of these supplements. Mero et al. (30) found that combining creatine and sodium bicarbonate supplementation, relative to placebo, increased 100-m swim performance. However, because there was no creatine alone treatment, it remains unclear whether combining these 2 supplements would have an additive effect on exercise performance. From a practical perspective, understanding the combined effects of these supplements may assist coaches and athletes in deciding which supplement (i.e., creatine, sodium bicarbonate, or combination) is best for increasing performance during high-intensity exercise.
The primary purpose of this study was to evaluate the impact of combining creatine monohydrate and sodium bicarbonate supplementation on exercise performance. We hypothesized that combining these 2 supplements, relative to placebo and creatine alone, would increase repeated sprint performance on a cycle ergometer, increase blood bicarbonate and pH, and decrease lactate concentrations.
Experimental Approach to the Problem
The focus of this study was to determine the impact of combining creatine and sodium bicarbonate supplementation on exercise performance. Using a double-blinded, crossover study design, the subjects completed an acute, 2-day supplement of a placebo, creatine, and creatine plus sodium bicarbonate condition. In the morning after each condition, the subjects completed six 10-second repeated sprints (i.e., Wingate tests) on a cycle ergometer and outcome measures were power output, pH, sodium bicarbonate, lactate, and perceptions of fatigue and gastrointestinal (GI) distress. From a practical perspective, the results of this study will provide an insight to the coach and athlete whether adding sodium bicarbonate to creatine supplementation is useful in increasing high-intensity exercise performance.
Thirteen healthy male participants between the ages of 18 and 30 were recruited from California Polytechnic State University and the surrounding area via e-mail and flyers (Table 1). Inclusion criteria included (a) V[Combining Dot Above]O2max >55 ml·(kg·min)−1; (b) >5 h·wk−1 of aerobic exercise; (c) no recent history of creatine monohydrate, sodium bicarbonate supplementation, or any other supplementation in the prior 6 months; (d) familiar with using a cycle ergometer; and (e) have no metabolic or chronic disease that would place the subject at risk of injury or interfere with exercise performance. Because data collection occurred in the spring months (March through May), all the subjects had a high level of aerobic exercise training (>5 h·wk−1), and were accustomed to high-intensity exercise (>2 h·wk−1). However, the subjects were in no specific training regimen throughout the study and were asked to maintain their typical training regimen. The Human Subject Committee at California Polytechnic State University approved this study, and each subject gave verbal and written consent to participate in the study pursuant to law.
The subjects completed a Physical Activity Readiness Questionnaire, a record of physical activity, and a health history questionnaire before participating in this study. The subjects then completed a graded exercise test on a cycle ergometer (Monarch 828 E, Langley, WA, USA) to determine peak oxygen consumption using the Astrand Bicycle Ergometer Maximal Protocol. Briefly, after a 5-minute warm-up, the subjects pedaled on the cycle ergometer at 100 W, and 50 W was added every 3 minutes. During the test, oxygen consumption and carbon dioxide production were assessed using an online metabolic system (Parvomedics TrueMax 2400, Consentius Technologies, Sandy, UT, USA), and V[Combining Dot Above]O2peak was defined as the highest V[Combining Dot Above]O2 value obtained (30-second average). The test continued until 3 of the after 4 conditions were met: (a) V[Combining Dot Above]O2 > 55 ml·kg−1·min−1, (b) respiratory exchange ratio > 1.15, (c) the subject's heart rate was within 5 beats of their age predicted max, and (d) the subject voluntarily stopped the test.
Using a double-blinded, crossover study design, the subjects completed an acute 2-day supplement of each of the following conditions: (a) placebo (Pl), (b) creatine alone (Cr), and (c) creatine + sodium bicarbonate (Cr + Sb). There was a 3-week washout period between each condition. The Pl consisted of 20 g of maltodextrin (Hammer Nutrition, Ltd., Whitefish, MT, USA) combined with an additional 0.5 g·kg−1 of maltodextrin. Cr consisted of 20 g of creatine monohydrate (CytoSport, Benecia, CA, USA) combined with an additional 0.5 g·kg−1 of maltodextrin. Cr + Sb consisted of 20 g of creatine monohydrate combined with an additional 0.5 g·kg−1 of sodium bicarbonate (Church & Dwight Co, Princeton, NJ, USA). The addition of 0.5 g·kg−1 of maltodextrin to PL and Cr was used to keep the volume consistent in each condition while also masking for the combined Cr + Sb supplementation. The total daily dose was divided equally into 4 smaller doses to be consumed throughout the day to minimize potential GI side effects. Each supplementation was ingested for 2 consecutive days, and the subjects were not given any supplement the morning of the exercise trials. All the supplements were unidentifiable in appearance and taste, which was determined after a pilot study taste test. On the first morning of each condition, the subjects were given the supplements along with information on how and when to take the supplements. The subjects were instructed to ingest each supplement at the following times: 9:00 am, 12:00 pm, 6:00 pm, and 10:00 pm. During each condition, the subjects completed a 48-hour dietary recall and were asked to consume similar food during each condition. The subjects were instructed and reported drinking (assessed by 48-hour dietary recall) at least 16 oz. of water during each ingestion and at least 2 L of water throughout each supplementation day to maintain adequate hydration. The subjects were also instructed to refrain from caffeine, alcohol, and exercise during the 48-hour supplementation period. Finally, the subjects were also instructed to maintain their current level of training or exercise similar throughout the entire 9-week study, which was assessed by a physical activity log.
After an overnight fast, on the morning after each condition (between 6 and 8 am), the subjects arrived at the Human Performance Laboratory. An initial blood capillary sample to assess pH, bicarbonate, and lactate concentrations was determined from a finger using a sterile lancet (see below for details). The subjects then performed six 10-second Wingate sprints on a Veletron Dynafit Pro cycle ergometer (RacerMate Inc, Seattle, WA, USA). The sprint test procedures started with a 5-minute warm-up at 50 W with three 5-second practice sprints. At the end of this warm-up, the test administrator gave a 10-second countdown for the subject to build up to their maximal effort and then the cycle ergometer magnetically added 0.075 kg·kg−1 of body weight of resistance immediately at the start of the sprint. The subjects were instructed to perform maximally throughout each 10-second sprint. Immediately after each 10-second sprint, a 60-second active recovery at 50 W was performed. Outcomes measures were peak power (watts), relative peak power (watts per kilogram), mean power (watts), relative mean power (watts per kilogram), and fatigue index (watts per second).
After the completion of each sprint, perceived feelings of fatigue and GI distress were assessed using a 0–10 rating scale (33). The questionnaire addressed upper abdominal problems (e.g., bloating, cramps, vomiting, or nausea) and lower abdominal problems (intestinal cramps, flatulence, or diarrhea). Systemic discomfort was assessed by rating any systemic issues (dizziness, headache, muscle cramp, or urge to urinate). Each question was rated on a 0- to 10-point scale ranging from 0 = no problem at all to 10 = the worst it has ever been. A final blood capillary sample was collected 5 minutes after the final sprint.
Blood samples were collected via finger stick, and blood pH, bicarbonate, and lactate samples were analyzed on an Abbott iSTAT Blood Gas Analyzer (Version 1 2006, Abbot Park, IL, USA). Blood samples were immediately applied to the iSTAT cartridge, and assessment of pH, bicarbonate, and lactate was made by ion-selective electrodes using the Nernst equation. The blood analyzer was calibrated before and at the end of the test session. Blood samples were recorded 5 minutes before the first Wingate sprint and 5 minutes after the sixth Wingate sprint.
All statistical analyses of data in this study were completed using SAS/Stat software, Version (9.2) for Windows (SAS Institute Inc., Cary, NC, USA). A repeated-measure analysis of variance (ANOVA) with a significance level of 0.05 and a power of 0.8 was used to test for carryover, sequence, period, condition, and sprint main effects. Also, a repeated-measure ANOVA was used to determine interactions (condition × sprint) for peak power, relative peak power, mean power, relative mean power, perceptions of fatigue, GI distress, pH, bicarbonate, and lactate concentrations. When appropriate, post hoc tests of significance were performed with a Tukey honestly significant difference test. Finally, we used an intraclass correlation coefficient (ICC), standard error of mean (SEM), and confidence intervals to determine the reproducibility of outcome measures from the same individual in a sequence.
There was no significant sequence or period effects for any of the response variables (p > 0.05). In addition, no carryover effects were observed, demonstrating that the 3-week washout period was sufficient.
A main effect for condition was observed in peak power output (Figure 1). Relative to Pl, peak power output was significantly higher in Cr + Sb but not Cr. Peak power was not different between Cr and Pl, and Cr and Cr + Sb. Each condition showed significantly lower peak power output in sprints 4–6 when compared with sprint 1 (data not shown). There was no significant interaction (condition × sprint) in peak power output (p > 0.05).
A main effect for condition was observed in relative peak power output (Figure 2). Relative peak power was significantly higher in Cr and Cr + Sb compared with Pl. There was no difference in relative peak power between Cr and Cr + Sb. In Pl and Cr, relative peak power in sprints 4–6 was significantly lower compared with sprint 1 (Figure 3). However, in Cr + Sb, only sprint 6 was different than sprint 1 in relative peak power (Figure 3). There was no significant interaction (condition × sprint) in relative peak power output (p > 0.05).
Relative to Pl, mean power was not different in Cr; however, mean power was significantly higher in Cr + Sb (660 ± 62, 673 ± 60, 682 ± 67 W, respectively). There was no significant difference between Cr and Cr + Sb (p > 0.05). Mean power in sprints 3–6 was significantly lower than sprints 1 and 2 in all 3 conditions (data not shown). There was no significant interaction (condition × sprint; p > 0.05) in mean power. No differences in relative mean power and fatigue index were found in any condition (data not shown).
Pretest Blood bicarbonate concentrations (Table 2) were significantly higher in Cr + Sb (∼10%) compared with Cr (p < 0.001) and Pl (p = 0.001). Postexercise bicarbonate concentrations were not different across conditions. Blood pH and lactate concentrations were not different across conditions (Table 2).
Perception of fatigue and GI distress was not different between Pl, Cr, and Cr + Sb (data not shown). However, in each condition perception of fatigue in sprints 3–6 were significantly higher than sprints 1 and 2 (data not shown). There was no significant interaction (p > 0.05) and no significant differences across conditions (p > 0.05) in upper abdominal, lower abdominal, and systemic areas of GI distress and systemic discomfort.
Reproducibility of Outcome Measures
The ICC (3,1) (35) values, 95% confidence intervals and SEM are reported in Table 3 for each outcome measure in the experiment. It is important to note that these data are assessing the reproducibility of outcome measures from the same individual in a sequence, and not the test-retest reliability. In general, we found that the subjects within a sequence have low similarity in outcome measures (Table 3).
The primary goal of this study was to examine the combined impact of sodium bicarbonate and creatine supplementation on exercise performance. The main findings were that combining these 2 supplements: (a) increased peak power and relative peak power compared with placebo and (b) had a greater attenuation of decline in relative peak power over 6 repeated sprints when compared with placebo and creatine alone. From a practical perspective, these data provide an insight to coaches and athletes that adding sodium bicarbonate to creatine may be more beneficial than creatine alone in increasing exercise performance.
A novel finding in this study is the clear difference in exercise performance when adding sodium bicarbonate to creatine supplementation. In this study, relative peak power was 7% higher in Cr + Sb than Pl during the repeated Wingate sprints, whereas Cr alone was only 4% higher than placebo. Furthermore, Cr + Sb had the greatest attenuation of decline in relative peak power over the 6 repeated sprints. In the one other study evaluating the combined impact of these 2 supplements, Mero et al. (30) found that combining creatine and sodium bicarbonate increased interval swim performance. To our knowledge, this study is the first to directly compare the effects of a combined creatine and sodium bicarbonate supplementation to creatine alone. Our results are consistent with and extend the findings of previous research (19,30,34,40) showing that adding sodium bicarbonate to creatine further increases power output and slows the rate of decline in relative peak power during repeated sprints.
In this study, the greater attenuation of decline in power output in Cr + Sb may be because of, at least partially, increased blood bicarbonate levels. Previous research has shown that ingesting sodium bicarbonate in 0.5 g·kg−1·d−1 raises blood bicarbonate concentrations (9,24,36). Using a similar dose, we found that resting blood bicarbonate was higher in Cr + Sb (+11%) and mean values remained higher after the last sprint, although not significantly. This, in theory, would allow for the greater efflux of hydrogen ions out of the muscle cell for greater work and intensity to be performed (7,22–29,34). It is important to note, from a practical perspective, that the greater attenuation of decline in power output in high-intensity exercise occurred without any significant GI side effects (assessed by questionnaire). These data are encouraging for coaches and athletes because previous studies have shown that sodium bicarbonate supplementation immediately before exercise increases GI side effects (28). In this study, ingesting 4 smaller amounts of sodium bicarbonate, but maintaining a similar overall dose as previous studies, minimizes these GI effects while potentially aiding in increasing exercise performance.
Even though the exact mechanism(s) of creatine and sodium bicarbonate to increase exercise performance remains unclear, it is generally assumed that these 2 supplements work in independent pathways. For example, creatine supplementation increases muscle creatine up to 20%, in which about 20% is stored in the form of phosphocreatine (PCr) (11–15,17). The increased PCr availability may allow for a more rapid resynthesis of ATP and aid in the shuttling of high-energy phosphates from the site of muscular contraction to the mitochondrial membrane where ATP is produced (6). Alternatively, sodium bicarbonate supplementation may increase buffering capacity in the blood and increase intracellular bicarbonate stores, which allows for greater efflux of hydrogen ions out of the muscle cell therefore decreasing fatigue and power output declines (34). Previous research suggests that sodium bicarbonate becomes increasingly important in the latter stages of repeated sprints at the point of which hydrogen ion accumulation is at its highest (7). In this study, the increased power output in Cr + Sb is consistent with creatine and sodium bicarbonate potentially working in independent pathways, and having an additional benefit on exercise performance.
In addition to the positive results found in Cr + Sb, we observed that only 2 days of Cr, without a loading phase, increased relative peak power (+6%) compared with placebo. Although the traditional loading dose of Cr (20–25 g for 4–7 days) has shown to increase exercise performance (14–19), little research has been conducted on the benefits of a smaller dosing period (<4 days). Ziegenfuss et al. (40) found that a shorter 3-day creatine supplementation resulted in significantly higher relative peak power than placebo in repeated sprint performance. Moreover, previous studies have shown that only 2 days of creatine supplementation is necessary to increase peak creatine uptake and PCr stores in muscle (14,39). Our results are generally consistent with other studies showing that an acute, 2-day dose of creatine supplementation without a loading phase increases exercise performance (8,10–17,32,37–39,40).
In this study, there are several limitations that need to be mentioned. First, even though all 13 subjects underwent the repeated sprints, blood samples were only taken before and after the 6 repeated sprint tests. Therefore, it remains unclear, the time course of blood pH and bicarbonate during the repeated sprints and the potential impact this would have on power output. Second, there was no sodium bicarbonate alone condition. Thus, there is no way to determine whether Cr + Sb is better at increasing exercise performance than sodium bicarbonate supplementation alone. Third, despite observing a 7% increase in relative peak power in Cr compared with Pl, no significant increases were observed in peak power, mean power, and fatigue index between Cr and Pl. Our acute, 2-day supplementation period may not have been long enough to observe changes in these variables. Finally, based on the ICC(3,1) (35) values, 95% confidence intervals and SEM, we found that the subjects within a sequence have high variability in some outcome measures. However, it is important to note that the ICC in this study is not a measure of the test-retest reliability. Because we were interested in determining the impact of Cr + Sb supplement on exercise performance, we had no “true” replication and cannot determine the test-retest reliability of our outcome measures.
Data from this study can be applied to coaches and athletes undergoing high-intensity repeated exercise bouts. Using a convenient, acute 2-day supplement of creatine and sodium bicarbonate, we observed increased relative peak power (+7%) during the repeated sprints. Although this may seem minimal, it may have a profound impact on increasing high-intensity exercise performance in a real-world competition. At the elite or collegiate level in athletics, seconds (or less) may be the difference in winning an event, and a 7% increase in power output may play a pivotal role in deciding the outcome. Furthermore, we found that the increase in exercise performance occurred without any additional increase in GI side effects. Thus, the real-world impact of these results is that a 2-day supplementation of combining creatine and sodium bicarbonate may be more beneficial than creatine alone without increasing GI side effects.
The authors thank all the subjects for their time and participation in this investigation. They are grateful to Robert Clark, Chris Borgard, James Ramirez, Jamie Benett, David Norris, and Derek Marks, for helping with various aspects of the study. The authors have no professional relationships with companies or manufacturers who will benefit from the results of this study, and the results of this study do not constitute endorsement of the product by the authors, National Strength and Conditioning Association and the Journal of Strength and Conditioning Research. There was no grant funding for this study.
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Keywords:© 2013 National Strength and Conditioning Association
exercise; ergogenic aid; wingate; blood pH