The Effect of Sodium Bicarbonate Ingestion on Prolonged High-Intensity Exercise Performance in Normoxia and Acute Normobaric Hypoxia

Abstract

Sodium bicarbonate (NaHCO3) is an extracellular buffer that can counteract disproportionate hydrogen (H+) cation production. This alkalising agent is commonly ingested to enhance the H+ efflux out of the working muscle to delay the onset of muscle fatigue by limiting intracellular acidosis during high intensity exercise. Previous research has demonstrated the ergogenic effects of NaHCO3 ingestion on short high-intensity exercise performance; however, few studies have explored the efficacy of NaHCO3 ingestion on prolonged high-intensity exercise performance, under either normoxic or hypoxia conditions. Therefore, the overarching aim of the present thesis was to determine the effect of a novel NaHCO3 ingestion strategy on prolonged high-intensity exercise performance in normoxia and normobaric hypoxic settings. Study 1 investigated the effects of 0.3 g·kg-1 body mass (BM) NaHCO3 mini-tablets in a carbohydrate (CHO) hydrogel (Maurten AB, Gothenburg, Sweden) on 40 km cycling time trial (TT) performance in normoxic conditions (20.93 FiO2) which proceeded at individual time to peak alkalosis. The results of this study demonstrated that NaHCO3 ingestion improved 40 km cycling TT performance at normoxia by 1.42% (~54 s) when compared to placebo. This performance improvement was likely aided by enhanced extracellular buffering capacity through increases in blood pH and blood HCO3- pre- exercise and throughout the TT. The ingestion of NaHCO3 also shifted the movement of strong ions, which resulted in increases in extracellular Na+ and reductions in extracellular K+, Cl-, and Ca2+ during the TT, which likely contributed to a greater ability to sustain muscle excitability when compared to placebo. Heart rate, VO2, RPE, and cadence did not differ between the TTs, likely indicating improved gross efficiency that contributed to the ergogenic effects of NaHCO3 ingestion. Since cyclists often compete at altitude, where acute hypoxia exacerbates H+ ion accumulation, it is important to determine whether NaHCO3 ingestion provides similar benefits in this environment. Therefore, Study 2 investigated the effect of NaHCO3 ingestion (0.3 g·kg-1 BM mini-tablets in a CHO hydrogel) on 40 km cycling TT performance in acute normobaric hypoxia (~1850 m above sea-level) which proceeded 90 min after ingestion. The results from this study observed similar ergogenic effects to those of Study 1 (1.20% improvement compared to placebo), whilst also increasing extracellular buffering capacity and apparent strong ion difference (SID) pre-exercise and during the TT when compared to placebo. Like Study 1, heart rate, VO2, cadence, and RPE were not significantly different between NaHCO3 and placebo, which may suggest enhanced gross efficiency given the improved performance following NaHCO3 ingestion. Although the first two studies in this thesis observed ergogenic effects of 0.3 g·kg-1 BM NaHCO3 mini-tablets on 40 km cycling TT performance in normoxic and hypoxic conditions, it is unclear whether additional NaHCO3 ingested during the TT would provide greater extracellular buffering capacity towards the latter stages of exercise, and therefore, offer greater performance benefits when compared to pre-exercise NaHCO3. Study 3 aimed to determine the effect of a novel “top- up” NaHCO3 (NaHCO3-Top) ingestion strategy in aqueous solution (0.1 g·kg-1 BM) consumed at 10 km of a 40 km cycling TT after pre-exercise (90 min) 0.3 g·kg-1 NaHCO3 mini-tablets in a CHO hydrogel in the same ambient conditions in Study 2 (~1850 m simulated altitude). This novel NaHCO3 ingestion strategy significantly improved 40 km cycling TT performance when compared to placebo; however, NaHCO3-Top did not offer significant performance improvements when compared to a sole acute dose of 0.3 g·kg-1 NaHCO3 mini-tablets in a CHO hydrogel ingested at 90 min pre-exercise. Extracellular buffering capacity was raised towards the latter stages of the TT following NaHCO3-Top when compared to pre-exercise 0.3 g·kg-1 NaHCO3; however, this enhancement may have been contradicted by the onset of gastrointestinal symptoms (GIS) since these symptoms were more than double when compared to sole acute 0.3 g·kg-1 NaHCO3. Given the greater GIS after top-up NaHCO3 and the lack of additional performance benefit when compared to a pre-exercise dose, “top-up” NaHCO3 may be unnecessary despite its enhanced buffering capacity during the latter stages of a 40 km TT in acute hypoxia. Collectively, these studies highlight the ergogenic effects and the likely mechanisms associated with the performance improvements following NaHCO3 ingestion on prolonged high intensity cycling performance at sea-level and acute normobaric hypoxia. Cyclists should therefore trial both strategies prior to important competition. Overall, these findings indicate that nutritionists, practitioners, and cyclists could therefore consider NaHCO3 ingestion for prolonged high-intensity exercise at sea-level and altitude.

Date of Award	2025
Original language	English
Awarding Institution	Edge Hill University
Supervisor	CRAIG BRIDGE (Director of Studies) & KELLY MARRIN (Supervisor)