The Effect of Sodium Bicarbonate Intake on Endurance Performance in Recreational Female Runners

Introduction Buffering Agents in Exercise Performance During high-intensity exercise, muscle fatigue occurs, negatively impacting both anaerobic and aerobic (endurance) exercise performance. One primary cause of muscle fatigue is metabolic acidosis, which arises from the accumulation of intracellular lactate and H+ ions (Freis et al., 2017; Krustrup et al., 2015). Since muscle acidity is regulated by intracellular and extracellular buffering systems, enhancing these systems is essential to sustain effective muscle contraction, delay fatigue, and thereby optimize performance in both anaerobic and high-intensity endurance exercises (Durkalec-Michalski et al., 2018a; 2018b).

Various ergogenic aids are utilized to boost intracellular and extracellular buffering capacity, with beta-alanine and sodium bicarbonate (SB) being two well-supported agents: Beta-alanine enhances intracellular buffering by increasing muscle carnosine levels, thereby preventing acidosis and improving performance (Trexler et al., 2015). SB primarily acts as an extracellular buffer, clearing H+ ions from the blood. This mechanism indirectly reduces H+ accumulation in muscles during intense exercise (Durkalec-Michalski et al., 2018a; 2018b). By preserving ATP production via glycolysis, this buffering action delays the onset of muscle fatigue during high-intensity exercises (Lancha Junior et al., 2015; Lopes-Silva et al., 2019).

Due to its ability to reduce lactate and H+ accumulation, research has predominantly focused on SB's effects on high-intensity, short-duration exercise (1-10 minutes) performance reliant on glycolytic metabolism (Delextrat et al., 2018; Driller et al., 2012; Gough et al., 2017). For example, 0.3 g/kg dose of SB intake improved total work output by enhancing buffering capacity in a 10 x 6-second sprint protocol (Miller et al., 2016). SB is thus commonly used for sports reliant on glycolytic metabolism, such as sprinting, middle-distance running, and combat sports. Additionally, SB may also be beneficial for longer endurance events (30-60 minutes) at the anaerobic threshold (AT), such as high-intensity interval training or long-distance endurance events concluding with a final sprint (Burke, 2013).

SB and Endurance Performance While long-duration endurance exercise (>30 minutes) is primarily driven by aerobic metabolism, anaerobic glycolysis also significantly contributes to energy production, leading to elevated blood lactate levels (Egger et al., 2014; Jones et al., 1977; McNaughton et al., 1999). Consequently, SB can help maintain optimal pH levels during endurance exercise, enhancing high-intensity performance at or near the aerobic threshold (Egger et al., 2014; Freis et al., 2017).

Studies have examined the effects of 0.2-0.3 g/kg SB intake on endurance performance near the lactate threshold in cycling and running, often comparing it to neutral (sodium chloride) or acidic (ammonium chloride) supplements. Findings indicate that while SB improves time to exhaustion, acidic agents can reduce it (George & MacLaren, 1988; Jones et al., 1977; Sutton et al., 1981). For instance, Egger et al. (2014) found that 0.3 g/kg SB intake one hour before exercise extended performance time during a test following a 30-minute exercise session at 95% anaerobic threshold.