Acute effect of sodium bicarbonate supplementation on the performance during CrossFit® training

Abstract

Aim:

To verify the acute effect of sodium bicarbonate (NaHCO3) supplementation on performance during CrossFit® workout.

Methods:

Nine experienced males (30.8 ± 3.5 years; 84.4 ± 9.5 kg; 177.5 ± 4.03 cm; 2.2 ± 1.0 years) in CrossFit® participated in this study. They were allocated to two conditions: a) supplementation with 0.3 g.kg-1 of body weight of NaHCO3 and b) supplementation with 0.045 g.kg-1 of body weight of sodium chloride (NaCl). Blood lactate was analyzed at two different moments: before (lac-pre) and after the training protocol (lac-post). The heart rate (HR) and the rating of perceived exertion (RPE) were also collected every two minutes during the execution of the training protocol, and the RPE was also collected after it was finished. At the end of the training protocol, a questionnaire to measure gastrointestinal side effects (GSE) was answered by the participants. Repetitions performed in the training protocol was computed to evaluate the performance during the workout.

Results:

The results showed that there were no differences found when comparing the conditions for all parameters. HR and RPE were different in the first few minutes (< 4-6 minutes) when compared to the final minutes (> 14 minutes) of the workout. The area under the curve of HR and RPE was significantly lower in the NaHCO3 condition.

Conclusion:

Acute NaHCO3 supplementation did not improve performance during workout ‘Cindy’ in experienced men. Supplementation also did not alter hemodynamic and perceptual parameters, nor did it cause any GSE. However, responses as a function of time were reduced with NaHCO3 supplementation.

Keywords:
alkalosis; gastrointestinal tolerability; high-intensity functional training; muscle fatigue; performance-enhancing substances

Introduction

Fatigue is one of the main factors that limit physical performance. Ways to decrease or delay fatigue have been extensively investigated¹-³. High-intensity modalities cause an accumulation of lactate and hydrogen ions (H⁺) due to the predominance of the lactic glycolytic system, which results in limited amounts of oxygen for the functioning muscle cells⁴. Increased acidification of the intracellular environment has a direct influence on the development and perception of fatigue⁵.

Among the proposed mechanisms, related to cell acidification described in the literature, are the inhibitory effect on the activity of enzymes involved in glycolysis and glycogenolysis⁶, decreased calcium release and uptake by the reticulum sarcoplasmic⁷,⁸, reduced sensitivity of contractile proteins to calcium⁷, inhibition of cross-bridge formation⁹ and increased ion efflux potassium¹⁰. However, our organism has intracellular (phosphate and dipeptide) and extracellular (bicarbonate - HCO₃ ^- and plasma proteins) buffering mechanisms that help promote acid-base homeostasis¹¹. The supplementation of sodium bicarbonate (NaHCO₃) increases the extracellular reserve of HCO₃ ^- which allows the formation of a positive electrochemical gradient of these ions out of the active muscle fibers¹². The effects of NaHCO₃ on sports performance have been investigated¹³-¹⁶. Lopes-Silva et al.¹³ showed that the NaHCO₃ supplementation increases glycolytic contribution and improves performance during simulated taekwondo combat.

CrossFit® is a functional training program, constantly varied and with high intensity performed through metabolic conditioning, gymnastics movements, and weightlifting¹⁷. Despite the increasing popularity of CrossFit® training, there is still a lack of research, using supplements for performance optimization. Durkalec-Michalski et al.¹⁴ were the only authors to investigate the effect of NaHCO₃ supplementation on a CrossFit® workout and found that supplementation, in a chronic regime, when performed in progressive doses, improved performance in a specific workout (‘Fight Gone Bad’).

CrossFit® training provides several possibilities for performance purposes, hence the need for further clarification on NaHCO₃ supplementation in different types of training such as shorter workouts (i.e. ‘Fran’ and ‘Grace’) and longer workouts (i.e. ‘Cindy’ and ‘Murph’) in order to optimize performance in the sport. However, there is a lack in the literature regarding the analysis of performance in CrossFit® training when supplemented with NaHCO₃. This study aimed to verify the acute effect of NaHCO₃ supplementation on the performance during CrossFit® workout. We hypothesized that NaHCO₃ supplementation would be effective in improving performance during CrossFit® workout.

Methods

Participants

Nine male (30.8 ± 3.5 years; 84.4 ± 9.5 kg; 177.56 ± 4.03 cm; 26.7 ± 2.2 kg/m²) with experience in CrossFit® training (2.2 ± 1.0 years of training experience), with minimum regularity of three uninterrupted months and a three-day weekly frequency, participated in this study. Before the study outset, the sample size was estimated using the G-Power package (version 3.1.9.2, Heinrich-Heine-Universitat in Dusseldorf, Germany)¹⁸, considering an effect size (f) = 0.6; power (1-β) = 0.80; α = 0.05; correction among repetition measures = 0.5 and nonsphericity correction = 1 calculated by the procedures suggested by Beck¹⁹. Inclusion criteria for participation were: (a) to be regularly enrolled in a CrossFit® affiliate box; (b) to be normotensive and have no cardiovascular problems; (c) not using medicinal drugs or any ergogenic resources that could interfere with performance and (d) answering negatively to all questions in the Physical Activity Readiness Questionnaire (PAR-Q). After agreeing to participate in the research, all signed a consent form and were informed of all procedures in accordance with the Declaration of Helsinki (2000) and approved by the Research Ethics Committee of the Santa Casa de Misericórdia Hospital of Juiz de Fora (protocol number 024/2011).

Experimental Design

A counterbalanced double-blind crossover design was used in this study which happened over three visits. An Anthropometric evaluation was performed on the first visit to characterize the sample. That same day, participants were also familiarized with the research protocols. All were instructed to complete a food record from the last 24 hours before the first training session and repeat the same meals before the second training session. The experimental procedures then occurred over two days, in different consecutive weeks, with a seven-day washout period between them. Participants were randomly divided into two conditions, experimental (NaHCO₃) and placebo (sodium chloride - NaCl).

In both conditions, blood samples were initially collected to measure blood lactate. Then, everyone performed a specific workout - ‘Cindy’. HR and RPE were measured during training. Three minutes after the end of the training, another blood lactate collection was done²⁰, and the gastrointestinal side effects (GSE) questionnaire was answered by the participants. A global view of the experimental design is presented in Figure 1.

Figure 1
Experimental design.

To standardize, participants were instructed to (a) not drink alcohol during their entire participation in the study; (b) come to the laboratory two hours after their last meal in the morning; (c) not to consume drinks and foods that contain caffeine, and (d) do not practice vigorous exercise 24 hours before the workout.

Anthropometric evaluation

To characterize the sample, the height of the participants was measured using a wall stadiometer, with a measurement range from 0 to 220 cm and a graduation of 1 mm (Seca®, Seca 206, Germany). Also, the total body mass was measured using a digital scale with a capacity of 150 kg (G-TECH®, Glass 7 FW, China). All measurements were performed by a single evaluator responsible and experienced in the collection procedures. The body mass index was calculated using the following formula: body mass/height².

Supplementation Protocol

The participants were subjected to two conditions with different supplements: experimental with 0.3 g.kg^-1 of the body weight of NaHCO₃ and placebo with 0.045 g.kg^-1 of the body weight of NaCl, that is, without any ergogenic effect¹⁶. The supplementation protocol used in both conditions was dissolved in 300 ml of mineral water (Crystal®, Brazil) with a pH of 7.28 and a lemon-flavored juice (Clight®, Brazil). This volume was divided into three doses of 100 ml, which were ingested with a 10-minute interval between them, totaling 30 minutes to complete the supplementation²¹. After ingesting all supplementation, participants waited for 60 minutes before the workout. The time for NaHCO₃ absorption and dissociation to blood concentration occurs between 60 to 90 minutes after ingestion^{3, 22}.

Training Protocol - ‘Cindy’

‘Cindy’ is a standardized CrossFit® workout, performed for 20 minutes AMRAP (as many repetitions as possible)¹⁷, with the combination of the following movements: 5 pull-ups, with the initial position hanging from the fixed bar, with elbows, extended, and the final position with the chin exceeding the bar; 10 push-ups, with body parallel to the ground and elbow extended, perform flexion of the elbows until the chest touches the floor; and 15 squats, in which the hip aligns with the knees and then a full extension. Initially, five minutes of joint mobility on the shoulders, hips, and ankles were performed. The number of repetitions performed in the workout was computed and a CrossFit® coach was responsible for analyzing and validating the technique for each repetition. Concentric muscle failure was allowed to occur, in which participants performed a self-selected rest. All participants had prior orientation on the technique of executing each movement and verbal encouragement during the workout.

Heart rate and Rating of Perceived Exertion

HR and RPE were measured every two minutes during the workout, using an HR-monitor (Polar®, FT 60, Finland) and the OMNI-RES scale²³, respectively. The peak HR (HR-peak), average HR (HR-av), average RPE (RPE-av), and RPE five minutes post-workout (RPE-post5) was recorded. The maximum HR was calculated using the formula: HR_max = 220 - age (years).

Regarding RPE, all the participants were oriented and familiarized with the scale, during one training session, and asked to determine the RPE as per the following instructions: (a) look at the illustrations and words to assist in the selection of a number from 0 to 10; (b) if you feel as shown in the illustration, that the effort is “extremely difficult”, indicate number 10; (c) if they felt that the effort is between “extremely easy” and “extremely difficult”, they should indicate a number between 0 and 10, gradually, according to the illustrative descriptors present on the scale.

Blood Lactate Assessment

Blood lactate was collected before and after the workout. The blood sample was collected by a puncture in the distal phalanx of the index finger of the participants in aseptic conditions using a lancet (Roche®, Accu-Chek Safe-T-Pro Uno, USA) and disposable gloves (Cremer®, Brazil). After discarding the first drop of blood, 25 μL of capillary blood was collected. For the determination of blood lactate, a portable lactate analyzer (Roche®, Accusport, USA) duly validated²⁴ was used. Before testing, the lactate analyzer was calibrated with different standard solutions of known lactate concentrations (2, 4, 8, and 10 mmol∙L^-1).

Gastrointestinal side effects

The participants answered the GSE questionnaire after the workout. The questionnaire was validated to measure gastrointestinal discomfort²⁵ and consists of a group of six items (nausea, stomach cramps, flatulence, belching, swelling, and diarrhea), describing common gastrointestinal symptoms. The numerical rating scale 0-10 (with zero reflecting no gastrointestinal discomfort and 10 indicating the most severe gastrointestinal discomfort) was used to classify the intensity of these symptoms²⁶.

Statistical analysis

To calculate inferential statistics for the data, the normality of the distribution was assessed with the Shapiro-Wilk test, and the homoscedasticity with Levene’s test. Blood lactate and HR were compared for the two conditions using a two-way analysis of variance (two-way ANOVA) with repeated measures (condition × time), followed by Bonferroni’s post-hoc. The sphericality of the variables was tested using the Mauchly’s test, in which we used Geisser-Greenhouse’s epsilon ^b to define the degrees of freedom. A paired t-test was used to compare performance through the maximum number of repetitions achieved in the workout, HR-av, HR-peak, and area under the curve (AUC) of HR between conditions. GSE, RPE-av, RPE-post5, and RPE-AUC were compared between the two conditions using Wilcoxon’s nonparametric test. To compare the RPE during the workout, Friedman’s non-parametric test was used. Pearson’s correlation coefficients were calculated to analyze the relationship between body weight and performance in both conditions. The R-values of 0.1, 0.3, 0.5, 0.7 and 0.9 were considered small, moderate, large, very large and extremely large, respectively²⁷. The ƒ² Cohen’s ES was calculated for the number of repetitions, HR-av, HR-peak, lactate, RPE-av, RPE-post5, and GSE to determine the magnitude of the differences. ES values of 0.2, 0.6, 1.2, 2.0, and 4.0 were considered small, moderate, large, very large, and extremely large, respectively²⁷. The significance level was 0.01 and the software used for data analysis was SPSS Statistics for Windows, version 21.0 (SPSS Inc., Chicago, IL, USA) and GraphPad (Prism 8.0.1, San Diego, CA, USA).

Results

Exercise Performance, Heart Rate, and Blood Lactate

The paired t-test did not indicate a difference between NaHCO₃ and placebo conditions for the maximum number of repetitions performed, HR-av, and HR-peak in the workout. Likewise, the two-way ANOVA with repeated measures showed that no significant interaction of lactate was found in relation to time × condition [F (1, 16) = 0.80; p = 0.384]. In addition, there were no differences between the conditions [F (1, 16) = 1.6; p = 0.227] for lactate-pre and lactate-post. The ƒ2 Cohen’s ES was small for performance, HR-av, HR-peak, lactate-pre, and lactate-post (Table 1).

Neither relationship was observed between body weight and number of repetitions in NaHCO₃ condition (r = -0.005; p = 0.988) and placebo condition (r = -0.001; p = 0.997).

Table 1
Performance results, HR, and Blood Lactate for the sodium bicarbonate and placebo conditions.

	NaHCO3	NaCl	p-value	ES
Performance (reps)	491.1 ± 119.2 (399-583)	488.8 ± 125.7 (392-585)	0.67	0.02
HR-av (bpm)	166.1 ± 9.5 (159-173)	167.6 ± 8.4 (161-174)	0.15	0.17
HR-peak (bpm)	177 ± 11 (168-186)	179 ± 8.9 (172-185)	0.50	0.21
HR-av (%)	87.7 ± 4 (85-91)	88.5 ± 3.5 (86-91)	0.33	0.22
HR-peak (%)	93.5 ± 5.1 (90-98)	94.3 ± 4.1 (91-98)	0.49	0.19
Lactate-pre (mmol∙L-1)	2.5 ± 0.8 (1.8-2.9)	2.3 ± 1 (1.6-2.9)	0.75	0.23
Lactate-post (mmol∙L-1)	14.9 ± 3.8 (11-17)	13.2 ± 2.9 (10-15.2)	0.22	0.53

• Values are expressed as mean ± standard deviation (lower-upper 95% CI of the mean); NaHCO₃ - sodium bicarbonate; NaCl - sodium chloride; ES - effect size; HR-av - heart rate average; HR-peak - heart rate peak; pre - before the training protocol; post - after the training protocol; reps - repetitions; bpm - beat per minute; % - percentage of maximum heart rate; mmol∙L^-1 - millimol per liter.

Figure 2 shows that the two-way ANOVA with repeated measures found a difference of lactate for the effect of time [F (1, 16) = 186; p < 0.001] in NaHCO₃ condition (p < 0.001) and placebo condition (p < 0.001).

Values are
expressed as mean ± standard deviation; BLa: Blood lactate; NaHCO3 - sodium bicarbonate; NaCl - sodium chloride; * Significantly difference compared with pre (p < 0.001).

Rating of Perceived Exertion and Gastrointestinal side effects

The Wilcoxon’s test did not indicate any differences between NaHCO3 and placebo conditions for RPE-av, RPE-post5, and GSE. Also, the ƒ2 Cohen’s ES was small for all perceptual responses, except for GSE where ƒ2 Cohen’s ES was considered moderate when comparing the conditions (Table 2).

Table 2
Perceptual responses for the sodium bicarbonate and placebo conditions.

	NaHCO3	NaCl	p-value	ES
RPE-av (AU)	6.80 (4.20 - 8.30)	7.40 (4.60 - 8.70)	0.15	0.45
RPE-post5 (AU)	5.00 (3.70 - 6.30)	5.00 (4.10 - 6.80)	0.27	0.24
GSE (AU)	6.00 (2.20 - 16.00)	3.00 (0.16 - 8.50)	0.22	0.69

• Values are expressed as median (lower-upper 95% CI of median). NaHCO₃ - sodium bicarbonate; NaCl - sodium chloride; RPE-av - the rating of perceived exertion average; RPE-post5 - the rating of perceived exertion 5 minutes after the training protocol; GSE - gastrointestinal side effects; AU - arbitrary units.

Heart rate and rating of perceived exertion in course of time

Mauchly’s test found a violation of sphericity for HR in course of time (p < 0.001) and condition × time (p < 0.001). No significant interaction HR was found during the workout in relation to time × condition [F_{Greenhouse-Geisser} (3.4, 28) = 0.81; p = 0.518]. There were no differences (p > 0.01) in the times when the NaHCO₃ condition was compared with the placebo condition (Figure 3A). However, the two-way ANOVA with repeated measures indicated a difference of [F_{Greenhouse-Geisser} (2.1, 17) = 113; p < 0.01] for the effect of time. HR measured at 2 and 4 minutes which was significantly lower (p < 0.007) than at 14 minutes. However, between 4 and 12 minutes, HR remained stable with no differences (p > 0.01). In the placebo condition, HR at 2 minutes was significantly lower (p < 0.006) when compared to measurements made after 16 minutes. It was also significantly lower between 4 and 10 minutes (p < 0.009) than at 20 minutes.

Friedman’s test indicated that there were no differences (p > 0.05) in the times when comparing the NaHCO₃ condition with the placebo condition (Figure 3B). However, the RPE showed a difference in the effect of time (p < 0.001). In both conditions, the RPE measured between 2 and 6 minutes was significantly lower (p < 0.009) when compared to the times after 14 minutes.

The paired t-test and Wilcoxon’s test indicated differences between NaHCO₃ and placebo conditions for HR-AUC (p = 0.008; ES = 0.303) and RPE-AUC (p = 0.003; ES = 0.256), respectively.

■ NaHCO3
sodium bicarbonate; γ NaCl - sodium chloride; (A) Values are expressed as mean ± standard deviation; (B) Values are expressed as median (lower-upper 95% CI of median); HR - heart rate; RPE - the rating of perceived exertion; bpm - beat per minute; AU - arbitrary units; * Significantly difference compared with NaHCO3 condition (p < 0.001).

Discussion

The present study aimed to verify the acute effect of NaHCO₃ supplementation on the performance during CrossFit® workout. We have not confirmed the hypothesis that NaHCO₃ supplementation could increase performance during ‘Cindy’ CrossFit® workout. The primary results showed that there was not a difference between the NaHCO₃ supplementation and placebo conditions related to the number of repetitions of HR-av, HR-peak, lactate, RPE-av, RPE-post5, and GSE. However, when the AUC was analyzed, HR and RPE were lower in the NaHCO₃ condition. As the AUC represented the total exposure of the workout for HR and RPE, we can consider that over time, NaHCO₃ supplementation showed lower cardiovascular work and less perceived effort at the end of the workout.

Blood lactate values increased significantly after the workout in both conditions. Both HR and RPE also showed some significant changes, during the workout regarding the effects of time. Although, a more favorable blood acid-base profile induced by NaHCO3 supplementation could positively contribute to delay the negative effects of acidosis on contractile and metabolic mechanisms, thus improving performance. This hypothesis was not confirmed by the present study.

Despite the alkalotic state, supposedly, induced in the bloodstream by NaHCO₃ supplementation, our results did not show the efficacy of the supplementation in relation to performance. One of the explanations may be related to the oxidative system, since its contribution promotes the removal of H⁺ ions, thus reducing the concentration gradient between the intracellular and extracellular medium²⁸. The ‘Cindy’ workout is based on anaerobic stimuli, but rest between concentric muscle failure and exercises is heavily influenced by aerobic pathways. Results of Feito et al.²⁹ suggest that oxygen uptake during the recovery period and total work completed during the trials were the best indicators, which can compromise the effectiveness of NaHCO₃ supplementation in the performance of the present study. Supporting, Northgraves et al.³⁰ showed that NaHCO₃ supplementation did not improve 40-km cycling time trial performance with characteristics of aerobic metabolism.

Previous results¹²,¹³,³¹ support that the ergogenic potential of NaHCO₃ supplementation depends on the predominant energy pathway in the activity. In CrossFit® training, Durkalec-Michalski et al.¹⁴ found an improvement in overall performance in the ‘Fight Gone Bad’ workout corresponding to 6% after NaHCO₃ supplementation. The total duration of ‘Fight Gone Bad’ is similar to ‘Cindy’ (17 and 20 minutes, respectively). This performance improvement might be explained by the use of supplementation in progressive doses, as the supplementation model differs from the model used in the present study or even by the characteristics of specific movements of each workout: movement with external load in ‘Fight Gone Bad’ and gymnastic movements in ‘Cindy’.

Although ‘Cindy’ is a long workout at a lesser pace, in the present study, blood lactate values have increased substantially in both conditions. However, higher blood lactate values were expected in the NaHCO₃ condition when compared with placebo, since the lactate efflux from muscle cells into the bloodstream is increased after NaHCO₃ supplementation³². The HCO₃ ^- levels are related to the activation of the monocarboxylate transporter, which transports the H⁺ ions and lactate from the sarcolemma to the bloodstream³³. However, trained individuals have better acidosis tolerance conditions than physically active or untrained individuals, which may be due to the fact that acute and chronic exercise increase monocarboxylate transporter activity³⁴. This would explain the lack of the ergogenic effect of NaHCO₃ supplementation in the present study. As our results, Correia-Oliveira et al.³⁵ found no differences in blood lactate values after a cycling time trial with a distance of 4 km and a duration of approximately six to seven minutes. In contrast, Ferreira et al.¹ showed that a higher dose of NaHCO₃ supplementation (0.3 g.kg^-1 of bodyweight of NaHCO₃) promoted high lactate levels after a test lasting approximately 70 seconds when compared to a lower dose of NaHCO₃ supplementation (0.1 g.kg^-1 of the body weight of NaHCO₃) and placebo.

HR differences during the workout seem to be related to the cadence of movement. A CrossFit® training program does not have a standard cadence. Each athlete, in a self-selected way, controls the intensity of the effort for better performance³⁶. As well as the present study, Durkalec-Michalski et al.¹⁴ did not show differences in the HR-av and HR-peak in an incremental cycling test. An interesting fact in the aforementioned study is that the HR values at the ventilatory threshold were similar to the HR-av values in the present study for CrossFit® training recreational practitioners, regardless of the condition. To check the behavior of HR over time, the AUC was evaluated, and that HR was lower in NaHCO₃ supplementation. This result has not yet been widely discussed in the literature, as previous studies with NaHCO₃ supplementation did not perform the analysis of AUC¹²,¹⁴.

RPE-av and RPE-post5 were not influenced by NaHCO₃ supplementation. Over time, the feeling of fatigue increases, regardless of whether the exercise is continuous or intermittent³⁷. The results of the present study corroborate those of other studies^{38, 39}, which did not observe differences in the RPE-av and RPE-post5. However, similarly, HR-AUC, RPE-AUC were lower in NaHCO₃ supplementation, in which the feeling of fatigue depended on metabolic, circulatory, and psychochemical aspects⁴⁰, which are summarized in the course of workout time. It is conceivable that a threshold change in pH or HCO₃ ^- is necessary to trigger an alteration in the peripheral sensation of exertion⁴¹.

The use of NaHCO₃ supplementation, depending on the dosage (i.e., doses above 0.3 g.kg^-1 of the body weight of NaHCO₃), may not be recommended, as there is an increase in the incidence of adverse effects, such as GSE⁴². A possible strategy, as previously reported, is to split the intake of supplementation into equal doses²¹. A higher incidence and severity of gastrointestinal symptoms after NaHCO₃ supplementation can negatively affect physical performance¹⁶. However, despite the lack of significance for GSE, the moderate effect size (ES = 0.69) incorporates the idea that GSE may have influenced performance, even if minimally, and is perhaps responsible for the lack of ergogenic effect of NaHCO₃ supplementation. Thus, alternatives such as testing supplementation during training before using it in competitive situations and the use of progressive doses of supplementation becomes relevant to the athlete’s good performance¹⁴.

Although this study provides practical and scientific evidence on the use of NaHCO₃ supplementation in practitioners trained in CrossFit® training, there are some limitations in this paper. Perhaps it would be more interesting if more blood collections were taken after the workout to analyze the lactate kinetics. Despite the sample calculation carried out a priori, perhaps the use of a small ES, which would represent more participants, could improve analysis regarding the benefit of supplementation on performance. As CrossFit® training is a program that involves several characteristics and elements, the analysis of the responses of sodium bicarbonate use in other workouts is necessary for better discussions about the results.

Conclusion

Acute NaHCO₃ supplementation did not improve performance in the ‘Cindy’ CrossFit® workout in experienced men. Hemodynamic and perceptual parameters were influenced by supplementation during a workout over the course of time and NaHCO₃ supplementation did not promote GSE.

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• Associate Editor:

  Ricardo Augusto Barbieri. Estácio UniSEB/Ribeirão Preto, SP, Brasil

• Acknowledgments:

  The authors would like to thank CrossFit Juiz de Fora for its support in the present study and each of the participants for their efforts.

Publication Dates

• Publication in this collection
  14 Dec 2020
• Date of issue
  2020

History

• Received
  20 Apr 2020
• Accepted
  24 Aug 2020