What this is
- This research evaluates the effects of co-ingesting caffeine and sodium bicarbonate on .
- Twenty-eight resistance-trained participants performed endurance tests on bench press and back squat exercises.
- Results indicate that caffeine enhances performance, but its benefits are negated when combined with sodium bicarbonate.
Essence
- Caffeine intake alone significantly improves performance, while co-ingestion with sodium bicarbonate does not provide added benefits and may reduce caffeine's effectiveness.
Key takeaways
- Caffeine increased the number of repetitions and power output in both bench press and back squat exercises. At 65% 1RM, caffeine improved repetitions by 7% in both exercises, while at 85% 1RM, it increased repetitions by 9.5% in bench press and 25% in back squat.
- Sodium bicarbonate did not enhance performance and may diminish the ergogenic effects of caffeine when taken together. No significant improvements were observed in repetitions or power output with sodium bicarbonate alone or in combination with caffeine.
Caveats
- The study did not measure plasma concentrations of caffeine or bicarbonate, limiting insights into their absorption and effectiveness. Additionally, the sample size may restrict the generalizability of the findings.
Definitions
- muscular endurance: The ability of a muscle or muscle group to maintain force output or perform repeated contractions against resistance over time.
AI simplified
1. Introduction
Caffeine and sodium bicarbonate (NaHCO3) are widely used supplements by athletes in various sports, such as swimming or cycling, due to their ability to enhance endurance capacity [1,2]. Since caffeine and NaHCO3 act through different physiological mechanisms [2,3,4], it is plausible that co-ingesting them could result in an additive ergogenic effect. Despite this potential, research examining the combination of these supplements in the context of muscular endurance remains limited.
Caffeine and NaHCO3 have improved performance in exercises lasting 30 s to 8 min [1,2]. Caffeine works by antagonizing adenosine receptors (A1 and A2A) in the central nervous system (CNS), which leads to reduced fatigue and perceived exertion, increased alertness and vigor, and enhanced recruitment of muscle fibers during contractions [2]. Additionally, caffeine may facilitate calcium (Ca2+) mobilization, increasing muscle ability to produce force and delaying fatigue by preventing a decline in Ca2+ availability [5]. On the other hand, NaHCO3 ergogenic effects occur through enhanced extracellular buffering, leading to increased extracellular pH and base excess, which assists in removing H+ and lactate from working muscles [6]. This mechanism improves intramuscular pH, promoting higher glycolytic rates [6], faster ATP resynthesis [7,8], and better utilization of Ca2+ to sustain performance and delay fatigue [3,4].
Although both caffeine and sodium bicarbonate (NaHCO3) have been shown to individually enhance exercise performance [1,2], their combined effects remain underexplored. Muscular endurance, defined as the ability of a muscle or muscle group to maintain force output or perform repeated contractions against resistance over time, has been investigated following isolated caffeine and NaHCO3 supplementation. Research on caffeine has examined a range of loads from 35% to 85% of one-repetition maximum (1RM) and various protocols, including single sets, multiple sets, and drop-sets, often reporting performance improvements [9,10]. However, the magnitude of these improvements appears to depend on the type of exercise, with lower-body movements, such as squats, showing greater benefits compared to upper-body exercises like the bench press [11]. Physiologically, caffeine’s ability to mitigate fatigue-related reductions in force production further highlights its potential to enhance muscular endurance [12].
Similarly, NaHCO3 has been shown to enhance muscular endurance by buffering the accumulation of H+ during exercise [13]. Studies using a wide range of loads (from 20% to 80%) and various protocols (e.g., single and multiple sets) have yielded conflicting results regarding NaHCO3’s efficacy in improving muscular endurance [14]. Some studies have found no significant performance enhancement following the intake of 0.3–0.4 g/kg of NaHCO3 60 to 90 min before exercise [15], while others have reported notable improvements [16]. A meta-analysis by Grgic et al. [14] concluded that a dosage of 0.3 g/kg NaHCO3, taken 60 to 180 min prior to exercise, could enhance muscular endurance, though not muscular strength.
Despite the available evidence on the individual effects of these supplements, no research has investigated their combined impact on muscular endurance. It is plausible thought that the co-ingestion of caffeine and NaHCO3 may promote additive ergogenic effects delaying muscular fatigue. The intramuscular accumulation of H+ caused by extenuating exercise would increase the competition between H+ and Ca2+ at the troponin-biding [17], inhibiting PCr resynthesis [18] and phosphofructokinase activity [6]. Thus, we hypothesized that the buffering capacity of NaHCO3 would facilitate the ability of caffeine to stimulate intramuscular Ca2+ availability and utilization, together with an improved ATP resynthesis, allowing the synergic ergogenic effect of the co-ingestion of NaHCO3 and caffeine. Consequently, the aim of this study was to evaluate the acute effects of co-ingesting caffeine and NaHCO3 on muscular endurance performance in resistance-trained males and females, at different loads in the bench press and back squat exercises.
2. Materials and Methods
2.1. Participants
A sample size of 24 participants was deemed adequate to compare the effects of the four supplement conditions and two exercise types across the two measurement points (65% and 85% 1RM), with an effect size of 0.3 (α = 0.05; 1 − β = 0.80) (v3.1, G*Power, Dusseldorf University, Düsseldorf, Germany) [19]. Finally, twenty-eight participants (age: 23 ± 4 years; sex ratio: 14 females and 14 males) completed the study. All participants were resistance-trained, with an average of 2.6 ± 1.2 years of structured resistance training experience. They trained their upper body 3.0 ± 1.4 days/week and their lower body 2.5 ± 1.6 days/week. The average 1-repetition maximum (1RM) relative per body mass was 0.99 ± 0.24 for the bench press and 1.40 ± 0.29 for the back squat. Participants’ dietary caffeine intake was 8.48 ± 8.0 mg/kg/day, as determined by a 24 h dietary recall. Eight out of the fourteen female participants began the trial during the follicular phase of their menstrual cycle.
To participate in the study, individuals had to meet the following criteria: (a) age between 18 and 35 years of age; (b) have no history of neuromuscular, musculoskeletal, neurological, immunological, or cardiometabolic disorders; (c) demonstrate the ability to perform back squats and bench press exercises with loads equivalent to at least 100% and 80% of their body weight, respectively; (d) possess a minimum of six months of prior resistance training experience and have trained at least three times per week over the past three months, as verified via questionnaire; and (e) refrain from using any medications, drugs, stimulants, or sports supplements throughout the duration of the study.
Before participation, all individuals were fully informed of the study’s procedures, potential risks, and any associated discomforts, after which they provided written consent. The study protocol adhered to the ethical principles outlined in the Declaration of Helsinki and received approval from the University Ethics Committee.
2.2. Experimental Design
The study employed a double-blind, placebo-controlled, randomized crossover design. Participants attended the laboratory on five different occasions. During the first visit, their body composition, dietary habits, and physical activity levels were evaluated. Additionally, a familiarization session was conducted, where a certified trainer assessed their back squat and bench press techniques, and their one-repetition maximum (1RM) for both exercises was determined.
For visits two through five, participants returned to the laboratory at the same time of day, performing four separate trials with at least 72 h between sessions to allow for full recovery and a washout period [8,20]. The four conditions tested included: (a) sodium bicarbonate combined with caffeine (NaHCO3 + CAF), (b) sodium bicarbonate alone (NaHCO3), (c) caffeine alone (CAF), and (d) a placebo (PLA). Each participant completed the trials in a randomized sequence, which was counterbalanced across the group using www.randomizer.org↗. An external researcher generated alphanumeric codes for participant identification and trial beverages to maintain blinding. These codes were only disclosed after the completion of statistical analyses.
2.3. Experimental Protocol
The experimental procedure of the trial is illustrated in Figure 1 and explained below.
2.3.1. Body Composition, Dietary and Physical Activity Habits
Participants attended a familiarization session in the laboratory one week before the initial experimental trial. Body composition was assessed using bioelectrical impedance analysis (Tanita BC-418, Tanita Corporation of America Inc., Chicago, IL, USA), as previously described in other studies [21], and body weight was utilized to determine individual supplement dosages. Dietary habits were analyzed using a 24 h dietary recall with MyFitnessPal software and DIAL (Alce Ingeniería, Madrid, Spain). Physical activity levels were measured using the International Physical Activity Questionnaire (IPAQ). Participants were instructed to abstain from consuming caffeine, stimulants, bicarbonate, alcohol, or engaging in intense physical exercise for 24 h leading up to the familiarization session and throughout the study period. Additionally, participants were required to maintain consistent dietary and sleep habits. Sleep patterns were self-reported through questionnaires, and diet and fluid intake were monitored using a 24 h dietary recall. Participants replicated their meals during the 24 h before each laboratory visit, particularly the two meals preceding the trials. To mitigate circadian variability, both familiarization and experimental trials were conducted at the same time of day.
2.3.2. Supplementation Protocol
The supplementation process began 120 min prior to each trial. Participants ingested either sodium bicarbonate (0.3 g/kg body weight) or a placebo (3 mg/kg maltodextrin, HSN, Granada, Spain) in two doses of 0.15 g/kg (or 1.5 mg/kg for the placebo), administered 120 and 90 min before the session. This method was designed to reduce gastrointestinal discomfort [22]. Sixty minutes before the trial, participants consumed either caffeine (3 mg/kg, HSN, Granada, Spain) or a placebo (3 mg/kg maltodextrin). All supplements were dissolved in 150 mL of water and flavored with a non-caloric additive to mask taste and odor (MyProtein, Northwich, UK). To maintain blinding, the beverages were served in opaque shaker bottles.
2.3.3. One Repetition Maximum (1RM)
The one-repetition maximum (1RM) for bench press and back squat exercises was assessed using a Smith machine (Multipower, Technogym, Barcelona, Spain), following protocols outlined in previous studies [23,24]. Participants were instructed to perform the eccentric phase in a controlled manner, pause for two seconds at the isometric phase, and then execute the concentric phase as quickly as possible. A linear transducer (Encoder, Chronojump Boscosystem, Collegno, Italy) measured the bar displacement velocity. Initial loads were set at 20 kg for males and 10 kg for females, increasing by 15–10 kg increments until the mean bar velocity (Vmean) reached 0.5 m/s for bench press and 0.8 m/s for back squat. To determine precise 1RM, smaller load increments (≤5 kg) were applied [23,24]. After a 20 min passive recovery period, participants completed a familiarization session, repeating the test sequence used during the experimental trials.
2.3.4. Muscular Endurance Tests
Following a standardized warm-up consisting of 10 min of dynamic stretching and joint mobility exercises, participants performed muscular endurance tests [11,24]. These included one set to failure at 65% and 85% 1RM for both the bench press and back squat. The load and exercise sequence remained consistent across all trials, with a five-minute passive recovery period between exercises and load conditions. During each attempt, participants were instructed to control the eccentric phase, pause for two seconds in the isometric phase, and perform the concentric phase at maximum speed while maintaining a consistent movement range. A linear encoder (Encoder, Chronojump Boscosystem, Italy) recorded variables such as mean velocity (Vmean), peak velocity (Vpeak), time to peak velocity (time to Vpeak), mean power (Wmean), peak power (Wpeak), time to peak power (time to Wpeak), and rate of power development (RPD). The lowest repetition count was used for comparison across experimental conditions, with the averages of the recorded variables calculated for analysis.
2.3.5. Questionnaires and Scales
Participants completed questionnaires at the end of the familiarization session and after each trial. These assessed perceived power, endurance, energy, muscular discomfort, gastrointestinal distress, rating of perceived exertion (RPE), heart rate, and other factors using a 1-to-10-point scale [25]. Mood was evaluated using an abbreviated version of the Profile of Mood States (POMS) and the Subjective Vitality Scale (SVS) [26]. To confirm the effectiveness of the blinding process, participants answered a specific question after each trial.
2.4. Statistical Analysis
The collected data were analyzed using SPSS version 27.0 (SPSS Inc., Chicago, IL, USA), and all visual representations were created with GraphPad Prism version 8 (GraphPad Software Inc., La Jolla, San Diego, CA, USA). Data normality was assessed using the Shapiro–Wilk test (p > 0.05). Muscular endurance performance was analyzed using a three-way repeated measures ANOVA based on supplement condition (NaHCO3 + CAF, NaHCO3, CAF, and PLA), load (65% and 85% 1RM), and exercise type (bench press and back squat). Sphericity was tested using Mauchly’s test, and violations were corrected using the Huynh-Feldt adjustment. The Holm-Bonferroni method was applied as a post hoc test where significant differences emerged. Cochran’s Q test was employed to analyze the effectiveness of blinding and supplement-related side effects.
Results are presented as mean ± standard deviation (SD), with statistical significance set at p < 0.05. Effect size (ES) was determined using partial eta squared (ηp2) for repeated measures ANOVA and Hedges’s g for pairwise comparisons. Effect size interpretations were defined as follows: trivial (0–0.19), small (0.20–0.49), medium (0.50–0.79), and large (≥0.80).
3. Results
No significant differences were found between the experimental conditions regarding body composition, dietary intake, or physical activity levels (Table 1).
3.1. Muscular Endurance
Supplement effect was detected in the number of repetitions (Reps, p < 0.001; ηp2 = 0.111; Figure 2), Vmean (p = 0.033; ηp2 = 0.115; Figure 3), Wmean (p = 0.047; ηp2 = 0.122; Figure 4) and Wpeak (p = 0.044; ηp2 = 0.106). Supplement plus exercise type (bench press vs. back squat) effect was detected in Reps (p < 0.001; ηp2 = 0.109; Figure 2), Vmean (p = 0.033; ηp2 = 0.115; Figure 3), Wmean (p = 0.026; ηp2 = 0.120; Figure 4) and Wpeak (p = 0.035; ηp2 = 0.112). These effects were irrespective to sex or load.
Compared to placebo, caffeine intake improved Reps (p = 0.035, g = 0.22), Vmean (p = 0.043, g = 0.16) and Wmean (p = 0.034, g = 0.15) and Wpeak (p = 0.040, g = 0.17) in back squat exercise. At 65% 1RM, caffeine increased Reps by 7% (p = 0.048, g = 0.78) in bench press and back squat (p = 0.044, g = 0.63), while, at 85% 1RM, caffeine increased Reps by 9.5% (p = 0.050, g = 0.82) in bench press and by 25% (p = 0.045, g = 0.42) in back squat compared to placebo. In contrast, compared to placebo, a non-statistically significant difference was found in NaHCO3 + CAF and NaHCO3 in bench press at 65%1RM (5% and 4 %, respectively) and 85%1RM (2.5% and 3.8%, respectively) as well as in back squat exercise at 65%1RM (5.7% and 7%, respectively) and at 85%1RM (1% and 7%, respectively).
Moreover, compared to placebo, caffeine intake improved Vmean (3.7%, p = 0.050, g = 1.144) and Wmean (5.2%, p = 0.047, g = 0.986) in back squat at 65%1RM, while at 85%1RM caffeine increased Vmean by 5.4% (p = 0.043, g = 0.22) and Wmean by (5.5%, p = 0.050, g = 0.25), as well as Vpeak by a 4.6% (p = 0.034, g = 0.23) and Wpeak by 7.1% (p = 0.022, g = 0.19).
3.2. Side-Effects Derived from Supplements Trials
The side effects questionnaire demonstrated a significant interaction effect for gastrointestinal discomfort (p = 0.014, ηp2 = 0.124) and muscular discomfort (p = 0.012, ηp2 = 0.162) following the trials. Pairwise comparisons revealed that gastrointestinal discomfort was significantly greater in the NaHCO3 + CAF condition compared to CAF alone (41%; p = 0.011, g = 0.82) and the placebo (52%; p = 0.029, g = 1.01). Similarly, NaHCO3 alone increased gastrointestinal discomfort relative to CAF (39%; p = 0.042, g = 0.912) and the placebo (51%; p = 0.012, g = 1.126). In terms of perceived energy, participants reported higher levels in the NaHCO3 + CAF condition (21%; p = 0.021, g = 0.643) and in the CAF condition (17%; p = 0.039, g = 0.445) compared to the placebo.
No significant differences were observed in mood-related variables, including depression, anger, vigor, fatigue, confusion, tension, or the Subjective Vitality Scale (SVS). Finally, 66% of participants accurately identified when they consumed NaHCO3, while 55% correctly recognized when they ingested CAF.
4. Discussion
The purpose of this study was to evaluate acute co-ingestion of caffeine and NaHCO3 effect on muscular endurance according to load in bench press and back squat exercise in male and female resistance-trained participants. The main outcome of this investigation shows that caffeine intake increased the number of repetitions, Vmean and Wmean, particularly in back squat exercise compared to bench press exercise similarly in male and female participants; however, this performance-enhancing effect was not observed when caffeine was ingested together with NaHCO3 or when NaHCO3 was ingested alone. Thus, acute caffeine and NaHCO3 co-ingestion does not cause a synergic effect on muscular endurance; in fact, it mitigates the ergogenic effect caused by caffeine.
Muscular endurance is a vital attribute in resistance training and various sports disciplines, as it supports the ability to sustain force and power output against a given load over an extended duration. This study investigated the impact of acute co-ingestion of caffeine and sodium bicarbonate (NaHCO3) on muscular endurance. The tests lasted approximately 36 s for sets at 65% 1RM and around 14 s for sets at 85% 1RM. Previous meta-analyses and systematic reviews report that caffeine consumption can enhance muscular endurance by about 6–7% [27], primarily due to an increase in the total repetitions completed per set following acute caffeine ingestion. However, limited research has examined multiple performance parameters, such as power and velocity, during muscular endurance testing across different loads. Existing studies indicate that caffeine can increase repetitions, velocity, and power output at 85% 1RM during the bench press exercise [28]. This effect may be less pronounced for lower body exercises, such as back squats, which involve larger muscle groups [11]. The results of this study are consistent with prior findings. Compared to the placebo condition, caffeine supplementation improved the number of repetitions in both bench press and back squat exercises across 65% 1RM and 85% 1RM loads, with gains ranging from 7% to 25%. Additionally, caffeine enhanced mean velocity (Vmean) and mean power (Wmean) in the back squat at 65% 1RM (by 3.7% and 5.2%, respectively) and at 85% 1RM (by 5.4% and 5.5%, respectively). These benefits are likely linked to caffeine’s role in increasing calcium (Ca2+) release from the sarcoplasmic reticulum, as caffeine binds to ryanodine receptor 1 [29]. Enhanced Ca2+ release and reutilization in skeletal muscle may explain the observed increase in repetitions across exercises and loads. Moreover, caffeine is known to improve motor unit recruitment and the conduction velocity of muscle fibers, which varies depending on the size of the muscle group [30]. Research suggests that muscle activation during maximal voluntary contractions (MVC) is generally lower in larger muscle groups, such as the knee extensors, compared to smaller muscle groups, like the ankle plantar flexors [31]. Therefore, if caffeine’s ergogenic effects occur via central nervous system (CNS) stimulation, larger muscle groups may experience a more significant boost in force production due to increased motor unit recruitment and firing rates compared to smaller muscle groups. In contrast, if caffeine exerts a direct effect on muscle, its ergogenic benefits should be consistent across different muscle groups, regardless of size. However, prior research supports the hypothesis of a central effect, showing a more substantial improvement in variables like mean power (Wmean), peak power (Wpeak), and peak velocity (Vpeak) in larger muscle groups, such as the quadriceps (back squat), compared to smaller muscle groups, like the pectoralis (bench press) [11]. This study further supports these findings by comparing the ergogenic effects of a 3 mg/kg caffeine dose on the bench press and back squat exercises. The results demonstrated a greater improvement in mean velocity (Vmean), peak velocity (Vpeak), mean power (Wmean), and peak power (Wpeak) for the back squat, particularly at 85% 1RM. Acute caffeine ingestion appears to delay fatigue onset, enabling participants to complete more repetitions in both upper- and lower-body exercises. However, the increase in power and velocity production was more pronounced in the back squat, which involves larger muscle groups. This pattern suggests that caffeine’s ergogenic effects involve both central and peripheral mechanisms. Specifically, the central effects of caffeine appear to improve power and velocity based on muscle group size, while its peripheral effects enhance endurance by increasing the number of repetitions performed, regardless of muscle group size.
Sodium bicarbonate intake increased the number of repetitions by 3–8% in the loads (65% and 85%1RM) and exercise types (bench press and back squat) evaluated; however, these differences were not statistically significant. Previous studies reported equivocal evidence regarding NaHCO3 erogenicity on muscular endurance after ingesting 0.3 g/kg of NaHCO3 from 60 to 90 min before three sets of back squat and bench press exercises at 80%1RM in eight resistance-trained men [16] or wrist flexion exercise in six recreationally active men [32]. In contrast, other studies are aligned with our results, not showing an effect of 0.3 g/kg of NaHCO3 intake from 105 to 120 min before 10RM of the bench and pull press exercises in eleven resistance-trained men [33], five sets of leg press with loads adjusted to perform 12 repetitions in fifteen resistance-trained men [34] or 1 set of leg press at 70%1RM in six recreationally active men [35]. Since blood bicarbonate levels were not measured in this study, it can be suggested that a 5–6 mmol/L increase in blood bicarbonate was not reached and thus may explain the limited ergogenic effect found after NaHCO3 intake [36], although others have questioned this idea [14]. Another potential explanation for the lack of effect observed could be that the NaHCO3 erogenicity may be greater for exercises that activate small muscle groups [37] since higher blood flow occurs when these muscle groups are exercised, resulting in greater ion exchange. Nonetheless, no differences were found in this study when comparing the quadriceps femoris and major pectoralis as the main muscles involved in the back squat and bench press exercises, respectively. This suggests that muscle size group may not be a major factor in NaHCO3 erogenicity. Nonetheless, it cannot be avoided that NaHCO3 seems to be more effective in ≥30 s duration tasks consistent with the alkalosis induced in exercise lasting 1–10 min [38] and ergogenic effect that has been previously noted in other repeated efforts (i.e., repeated 30 s sprint tests) [39]. Therefore, future studies should explore resistance exercise protocols performing a higher number of sets (e.g., 3–4 sets) using a moderate load (e.g., 60–70% 1RM) that allows a sufficient effort duration (>30 s) with a rest interval between sets (e.g., ~1.5 min) that facilitates a pronounced reduction in pH levels to promote the buffering capacity of NaHCO3 [40].
The acute co-ingestion of NaHCO3 and caffeine did not lead to a significant improvement in the number of repetitions compared to placebo without altering mean velocity or power of force production. Although, to our knowledge, no previous studies analyzed the combined effect of NaHCO3 and caffeine on muscular endurance, some studies have utilized this supplement protocol in disciplines where muscular endurance is required, such as judo, where the synergic effect was found in ten male judokas who improved Special Judo Fitness Tests performance after ingesting 0.3 g/kg of NaHCO3 three days before the exercise session plus 0.1 g/kg the day of the testing in three occasions 120, 90 and 60 min and 6 mg/kg of caffeine 50 min before the trial [22].
However, this effect was not evident when administering caffeine doses of 3–6 mg/kg combined with 0.3 g/kg of sodium bicarbonate (NaHCO3), provided in one or multiple doses between 120 and 60 min before testing. Similar outcomes were reported in twelve elite rowers following a 6 min rowing test [41], ten trained cyclists during a 3 km time trial [42], thirteen untrained participants cycling to volitional exhaustion [43], and eight karate athletes performing a sport-specific aerobic test [44]. In this study, no additive effect was observed when consuming caffeine and NaHCO3; in fact, the ergogenic effect observed after caffeine ingestion in Vmean and Wmean was mitigated when this supplement was consumed together with NaHCO3. Peak plasma concentrations of caffeine normally occur between 45 and 120 min after oral ingestion; this variation in time may be dependent on gastric emptying time and the presence of other dietary constituents. Additionally, while caffeine stimulates gastric acid secretion [45], NaHCO3 neutralizes the increase in pH caused by gastric acid [46]. Collectively, a potential explanation for the lack of effect on NaHCO3 + CAF compared to the CAF condition observed may be attributable to the fact that NaHCO3 ingestion could delay caffeine absorption and bioavailability in blood when is co-ingested with NaHCO3. This may also explain, at least in part, the equivocal evidence found in the literature in studies providing acute caffeine and NaHCO3 co-ingestion with performance-enhancing purposes. Nonetheless, this idea required further studies to explore the pharmacokinetics and pharmacodynamics of these dietary supplements when consumed together.
A key limitation of this study was the inability to measure plasma concentrations of caffeine, bicarbonate, and pH. These measurements could have offered important insights into the absorption, effectiveness of the supplements, and any potential pharmacokinetic or pharmacodynamic interactions. Sodium bicarbonate could interact with caffeine by increasing gastric pH, which can alter caffeine’s solubility and absorption rate [47], by alkalinizing urine that may affect caffeine’s renal clearance and metabolism [48], and by affecting CYP1A2 enzyme activity through pH alterations, which could influence caffeine’s metabolism [49]. Additionally, another limitation was the lack of measurement of other blood markers (e.g., LDH or CK) that would increase the understanding of the fatigue caused by the exercise protocol performed in this study.
5. Conclusions
The combined intake of caffeine and sodium bicarbonate (NaHCO3) did not result in an additive ergogenic effect on muscular endurance performance. A key finding of this study was that caffeine alone enhanced the number of repetitions, average velocity, and power output in both male and female participants, with a more notable effect observed in the back squat compared to the bench press exercise. Although NaHCO3 did not improve muscular endurance performance, in fact, this substance mitigated caffeine’s ergogenic effect when both supplements were co-ingested. Therefore, based on the current results, we recommend the ingestion of caffeine but not combined with NaHCO3 before any sport where muscular endurance plays a critical role in performance (e.g., CrossFit or rowing).