The time to peak blood bicarbonate (HCO3−), pH, and strong ion difference (SID) following sodium bicarbonate (NaHCO3) ingestion in highly trained adolescent swimmers

Background Contemporary research suggests that the optimal timing of sodium bicarbonate (NaHCO3) should be based upon an individual time in which bicarbonate (HCO3−) or pH peaks within the blood. However, the mechanisms surrounding acidosis on exercise performance are contested, therefore it is plausible that the ergogenic effects of NaHCO3 are instead a result of an increased strong ion difference (SID) following ingestion. Since the post-ingestion time course of the SID is currently unknown, the purpose of this study was to investigate the pharmacokinetics of the SID in direct comparison to HCO3− and pH. Methods Twelve highly trained, adolescent swimmers (age: 15.9 ± 1.0 yrs, body mass: 65.3 ± 9.6 kg) consumed their typical pre-competition nutrition before ingesting 0.3 g·kg BM-1 NaHCO3 in gelatine capsules. Capillary blood samples were then taken during quiet, seated rest on nine occasions (0, 60, 75, 90, 105, 120, 135, 150, and 165 min post-ingestion) for the assessment of time course changes in HCO3−, pH, and the SID. Results On a group mean level, no differences were found in the time in which each variable peaked within the blood (HCO3− = 130 ± 35 min, pH = 120 ± 38 min, SID = 96 ± 35 min; p = 0.06). A large effect size was calculated between the timing of peak HCO3− and the SID (g = 0.91), however, suggesting that a difference may occur between these two measures in practice. Conclusions A time difference between peak HCO3− and the SID presents an interesting avenue for further research since an approach based upon individual increases in extracellular SID has yet to be investigated. Future studies should therefore compare these dosing strategies directly to elucidate whether either one is more ergogenic for exercise performance.


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Introduction 42 Sodium bicarbonate (NaHCO 3 ) is recommended to athletes based upon adequate evidence of a 43 performance enhancing effect [1]. It is well acknowledged that NaHCO 3 ingestion increases buffering 44 capacity by increasing bicarbonate (HCO 3 -) and pH concentrations within the blood, although the 45 magnitude of these increases is variable between individuals [2,3]. Increasing blood alkalosis alters the 46 pH gradient between the intracellular and extracellular compartments, subsequently leading to the 47 upregulation of the lactate-hydrogen ion (H + ) co-transporter to efflux acidic H + from the active 48 musculature and into circulation [4,5]. During exercise, accelerating the removal of H + is purported to 49 offset fatigue since intracellular acidosis is associated with debilitating effects on the capacity to sustain 50 muscle force production [6-10]. More specifically, cellular acidosis is suggested to reduce muscle 51 shortening velocity and cross-bridge cycling by inhibiting calcium ion (Ca 2+ ) sensitivity [6,9] and myosin 52 ATPase activity [10,11], whereas additional impairments of key glycolytic enzymes [12,13] and the 53 strong ion difference (SID) [7,14,15] could reduce the available ATP substrates and action potentials 54 necessary to maintain muscular contractions, respectively. Due to the complexity of fatigue, the role of 55 acidosis in each of these mechanisms is contested as a causative factor [16][17][18]. However, since 56 NaHCO 3 continues to provide a strong ergogenic benefit to exercise, further investigation is warranted 57 concerning the biochemical changes that occur following ingestion.

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There is an apparent increase in the ergogenic potential of NaHCO 3 when blood HCO 3increases above 59 baseline concentrations by 5 mmol•L -1 , whereas increases above 6 mmol•L -1 are associated with almost 60 certain performance enhancement [19,20]. However, the time taken to reach these thresholds varies

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It is therefore plausible that another mechanism besides those associated with increased HCO 3is 72 involved with the ergogenic properties of NaHCO 3 supplementation.

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Alternatively, NaHCO 3 may mitigate fatigue by altering the intracellular and extracellular balance of 74 strong ions such as potassium (K + ), sodium (Na + ), chloride (Cl -), and Ca 2+ [26]. Indeed, NaHCO 3 is 75 suggested to maintain muscle excitability by increasing the influx of K + into the muscle following 76 ingestion and attenuating losses in intramuscular K + during exercise [27][28][29][30]. A concomitant increase in 77 muscular Cluptake is also observed [27,29,30], which is suspected to work synergistically with K + to 78 protect force and excitability when muscles begin to depolarise [31]. This effect is further strengthened 79 by an increased plasma Na + [2,3,27,28], which together with changes in K + and Cl -, could indicate an 80 upregulation of Na + /K + -ATPase and Na + /K + /2Cl --ATPase activity to limit depolarisation and preserve 81   . Similarly, water was permitted to be consumed ad libitum (mean intake: 140 1.2 ± 0.5 L, range: 0.5 -2.0 L), though ingestion of further nutrients were restricted once NaHCO 3 had 141 been consumed and blood changes were being monitored. Participants were also asked to refrain from 142 additional exercise outside of their regular swim training programme in the 48 hours prior to participating 143 in the study. No swimmers had ingested caffeine, although the consumption of creatine (participants 5, 144 8, 9, 10, and 11) and beta-alanine (participants 9 and 10) were reported. Since co-ingestion of multiple 145 ergogenic aids is common in high-level sport, these participants were included in subgroup analysis 146 rather than excluded from the study altogether. All trials were carried out between December 2019 and 147 February 2020 during a specific race preparation training period (weekly swimming volume = 50.9 ± 3.4 148 km    to detect statistical significances for all metabolites, therefore group level results are described using 225 effect sizes (Fig 3). This analysis showed that K + reduced gradually from baseline before reaching peak

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This was the first study to compare the time to peak of three methods of measuring peak alkalosis (i.e., confounded by a small sample size (n = 6) and a greater age and potentially maturational status (+2 293 yrs) of the non-supplement subgroup, it is important to consider that highly trained adolescents will likely 294 be consuming multiple ergogenic aids at times of competition [45]. Sports nutritionists should therefore 295 aim to seek the time to peak of their athletes whilst they are in full competition preparation to minimise 296 variations at competitive events.

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The SID of highly trained adolescent swimmers was increased by NaHCO 3 ingestion, albeit with a large 298 individual variability in the time to peak (60 -165 min

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The process of identifying a true peak HCO 3measurement has recently been criticised when using 349 NaHCO 3 capsules since these produce large increases in HCO 3 -(>5 mmol•L -1 ) for periods exceeding

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This study shows that highly trained adolescent athletes have marked increases and highly individual 367 time course changes in blood HCO 3 -, pH, and SID following the ingestion of NaHCO 3 capsules.

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Importantly, the post-ingestion time point in which the individual time to peak occurred for HCO 3and 369 the SID was separated by a large effect size. Given that the effects of acidosis on exercise performance 370 are controversial, this finding suggests that using a time to peak SID approach could be a more 371 appropriate NaHCO 3 ingestion strategy in practice. Consequently, future research should directly 372 compare ingestion strategies based upon individual time to peak HCO 3and SID to elucidate whether 373 either approach has an any further ergogenic benefits on exercise performance. In addition, this study 374 refutes the claim that NaHCO 3 capsule ingestion produces a long lasting 'ergogenic window', supporting 375 the need for adolescent athletes to identify their individual time to peak prior to use. It is acknowledged 376 that a lack of control surrounding pre-ingestion food, fluid, and supplement intakes likely influenced the 377 findings of this study, however, these conditions better replicate the actual changes that would occur 378 when athletes are in full competition preparation.