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1.
Heat Adaptation for Females: A Systematic Review and Meta-Analysis of Physiological Adaptations and Exercise Performance in the Heat.
Kelly, MK, Bowe, SJ, Jardine, WT, Condo, D, Guy, JH, Snow, RJ, Carr, AJ
Sports medicine (Auckland, N.Z.). 2023;(7):1395-1421
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Abstract
BACKGROUND Heat adaptation regimes are used to prepare athletes for exercise in hot conditions to limit a decrement in exercise performance. However, the heat adaptation literature mostly focuses on males, and consequently, current heat adaptation guidelines may not be optimal for females when accounting for the biological and phenotypical differences between sexes. OBJECTIVES We aimed to examine: (1) the effects of heat adaptation on physiological adaptations in females; (2) the impact of heat adaptation on performance test outcomes in the heat; and (3) the impact of various moderators, including duration (minutes and/or days), total heat dose (°C.min), exercise intensity (kcal.min-1), total energy expended (kcal), frequency of heat exposures and training status on the physiological adaptations in the heat. METHODS SPORTDiscus, MEDLINE Complete and Embase databases were searched to December 2022. Random-effects meta-analyses for resting and exercise core temperature, skin temperature, heart rate, sweat rate, plasma volume and performance tests in the heat were completed using Stata Statistical Software: Release 17. Sub-group meta-analyses were performed to explore the effect of duration, total heat dose, exercise intensity, total energy expended, frequency of heat exposure and training status on resting and exercise core temperature, skin temperature, heart rate and sweat rate. An explorative meta-regression was conducted to determine the effects of physiological adaptations on performance test outcomes in the heat following heat adaptation. RESULTS Thirty studies were included in the systematic review; 22 studies were meta-analysed. After heat adaptation, a reduction in resting core temperature (effect size [ES] = - 0.45; 95% confidence interval [CI] - 0.69, - 0.22; p < 0.001), exercise core temperature (ES = - 0.81; 95% CI - 1.01, - 0.60; p < 0.001), skin temperature (ES = - 0.64; 95% CI - 0.79, - 0.48; p < 0.001), heart rate (ES = - 0.60; 95% CI - 0.74, - 0.45; p < 0.001) and an increase in sweat rate (ES = 0.53; 95% CI 0.21, 0.85; p = 0.001) were identified in females. There was no change in plasma volume (ES = - 0.03; 95% CI - 0.31, 0.25; p = 0.835), whilst performance test outcomes were improved following heat adaptation (ES = 1.00; 95% CI 0.56, 1.45; p < 0.001). Across all moderators, physiological adaptations were more consistently observed following durations of 451-900 min and/or 8-14 days, exercise intensity ≥ 3.5 kcal.min-1, total energy expended ≥ 3038 kcal, consecutive (daily) frequency and total heat dose ≥ 23,000 °C.min. The magnitude of change in performance test outcomes in the heat was associated with a reduction in heart rate following heat adaptation (standardised mean difference = - 10 beats.min-1; 95% CI - 19, - 1; p = 0.031). CONCLUSIONS Heat adaptation regimes induce physiological adaptations beneficial to thermoregulation and performance test outcomes in the heat in females. Sport coaches and applied sport practitioners can utilise the framework developed in this review to design and implement heat adaptation strategies for females.
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Use of Buffers in Specific Contexts: Highly Trained Female Athletes, Extreme Environments and Combined Buffering Agents-A Narrative Review.
Carr, AJ, McKay, AKA, Burke, LM, Smith, ES, Urwin, CS, Convit, L, Jardine, WT, Kelly, MK, Saunders, B
Sports medicine (Auckland, N.Z.). 2023;(Suppl 1):25-48
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Abstract
This narrative review evaluated the evidence for buffering agents (sodium bicarbonate, sodium citrate and beta-alanine), with specific consideration of three discrete scenarios: female athletes, extreme environments and combined buffering agents. Studies were screened according to exclusion and inclusion criteria and were analysed on three levels: (1) moderating variables (supplement dose and timing, and exercise test duration and intensity), (2) design factors (e.g., use of crossover or matched group study design, familiarisation trials) and (3) athlete-specific factors (recruitment of highly trained participants, buffering capacity and reported performance improvements). Only 19% of the included studies for the three buffering agents reported a performance benefit, and only 10% recruited highly trained athletes. This low transferability of research findings to athletes' real-world practices may be due to factors including the small number of sodium citrate studies in females (n = 2), no studies controlling for the menstrual cycle (MC) or menstrual status using methods described in recently established frameworks, and the limited number of beta-alanine studies using performance tests replicating real-world performance efforts (n = 3). We recommend further research into buffering agents in highly trained female athletes that control or account for the MC, studies that replicate the demands of athletes' heat and altitude camps, and investigations of highly trained athletes' use of combined buffering agents. In a practical context, we recommend developing evidence-based buffering protocols for individual athletes which feature co-supplementation with other evidence-based products, reduce the likelihood of side-effects, and optimise key moderating factors: supplement dose and timing, and exercise duration and intensity.
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A Comparison of Sodium Citrate and Sodium Bicarbonate Ingestion: Blood Alkalosis and Gastrointestinal Symptoms.
Urwin, CS, Snow, RJ, Condo, D, Snipe, RMJ, Wadley, GD, Convit, L, Carr, AJ
International journal of sport nutrition and exercise metabolism. 2023;(1):1-10
Abstract
This study compared the recommended dose of sodium citrate (SC, 500 mg/kg body mass) and sodium bicarbonate (SB, 300 mg/kg body mass) for blood alkalosis (blood [HCO3-]) and gastrointestinal symptoms (GIS; number and severity). Sixteen healthy individuals ingested the supplements in a randomized, crossover design. Gelatin capsules were ingested over 15 min alongside a carbohydrate-rich meal, after which participants remained seated for forearm venous blood sample collection and completion of GIS questionnaires every 30 min for 300 min. Time-course and session value (i.e., peak and time to peak) comparisons of SC and SB supplementation were performed using linear mixed models. Peak blood [HCO3-] was similar for SC (mean 34.2, 95% confidence intervals [33.4, 35.0] mmol/L) and SB (mean 33.6, 95% confidence intervals [32.8, 34.5] mmol/L, p = .308), as was delta blood [HCO3-] (SC = 7.9 mmol/L; SB = 7.3 mmol/L, p = .478). Blood [HCO3-] was ≥6 mmol/L above baseline from 180 to 240 min postingestion for SC, significantly later than for SB (120-180 min; p < .001). GIS were mostly minor, and peaked 80-90 min postingestion for SC, and 35-50 min postingestion for SB. There were no significant differences for the number or severity of GIS reported (p > .05 for all parameters). In summary, the recommended doses of SC and SB induce similar blood alkalosis and GIS, but with a different time course.
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The Effect of Pre-Exercise Hyperhydration on Exercise Performance, Physiological Outcomes and Gastrointestinal Symptoms: A Systematic Review.
Jardine, WT, Aisbett, B, Kelly, MK, Burke, LM, Ross, ML, Condo, D, Périard, JD, Carr, AJ
Sports medicine (Auckland, N.Z.). 2023;(11):2111-2134
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Abstract
BACKGROUND Fluid loss during prolonged exercise in hot conditions poses thermoregulatory and cardiovascular challenges for athletes that can lead to impaired performance. Pre-exercise hyperhydration using nutritional aids is a strategy that may prevent or delay the adverse effects of dehydration and attenuate the impact of heat stress on exercise performance. OBJECTIVES The aim of this systematic review was to examine the current literature to determine the effect of pre-exercise hyperhydration on performance, key physiological responses and gastrointestinal symptoms. METHODS English language, full-text articles that compared the intervention with a baseline or placebo condition were included. An electronic search of Medline Complete, SPORTDiscus and Embase were used to identify articles with the final search conducted on 11 October 2022. Studies were assessed using the American Dietetic Association Quality Criteria Checklist. RESULTS Thirty-eight studies involving 403 participants (n = 361 males) were included in this review (n = 22 assessed exercise performance or capacity). Two studies reported an improvement in time-trial performance (range 5.7-11.4%), three studies reported an improvement in total work completed (kJ) (range 4-5%) and five studies reported an increase in exercise capacity (range 14.3-26.2%). During constant work rate exercise, nine studies observed a reduced mean heart rate (range 3-11 beats min-1), and eight studies reported a reduced mean core temperature (range 0.1-0.8 °C). Ten studies reported an increase in plasma volume (range 3.5-12.6%) compared with a control. Gastrointestinal symptoms were reported in 26 studies, with differences in severity potentially associated with factors within the ingestion protocol of each study (e.g. treatment, dose, ingestion rate). CONCLUSIONS Pre-exercise hyperhydration may improve exercise capacity during constant work rate exercise due to a reduced heart rate and core temperature, stemming from an acute increase in plasma volume. The combination of different osmotic aids (e.g. glycerol and sodium) may enhance fluid retention and this area should continue to be explored. Future research should utilise valid and reliable methods of assessing gastrointestinal symptoms. Furthermore, studies should investigate the effect of hyperhydration on different exercise modalities whilst implementing a strong level of blinding. Finally, females are vastly underrepresented, and this remains a key area of interest in this area.
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Does varying the ingestion period of sodium citrate influence blood alkalosis and gastrointestinal symptoms?
Urwin, CS, Snow, RJ, Orellana, L, Condo, D, Wadley, GD, Carr, AJ
PloS one. 2021;(5):e0251808
Abstract
OBJECTIVES To compare blood alkalosis, gastrointestinal symptoms and indicators of strong ion difference after ingestion of 500 mg.kg-1 BM sodium citrate over four different periods. METHODS Sixteen healthy and active participants ingested 500 mg.kg-1 BM sodium citrate in gelatine capsules over a 15, 30, 45 or 60 min period using a randomized cross-over experimental design. Gastrointestinal symptoms questionnaires and venous blood samples were collected before ingestion, immediately post-ingestion, and every 30 min for 480 min post-ingestion. Blood samples were analysed for blood pH, [HCO3-], [Na+], [Cl-] and plasma [citrate]. Linear mixed models were used to estimate the effect of the ingestion protocols. RESULTS For all treatments, blood [HCO3-] was significantly elevated above baseline for the entire 480 min post-ingestion period, and peak occurred 180 min post-ingestion. Blood [HCO3-] and pH were significantly elevated above baseline and not significantly below the peak between 150-270 min post-ingestion. Furthermore, blood pH and [HCO3-] were significantly lower for the 60 min ingestion period when compared to the other treatments. Gastrointestinal symptoms were minor for all treatments; the mean total session symptoms ratings (all times summed together) were between 9.8 and 11.6 from a maximum possible rating of 720. CONCLUSION Based on the findings of this investigation, sodium citrate should be ingested over a period of less than 60 min (15, 30 or 45 min), and completed 150-270 min before exercise.
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Factors Influencing Blood Alkalosis and Other Physiological Responses, Gastrointestinal Symptoms, and Exercise Performance Following Sodium Citrate Supplementation: A Review.
Urwin, CS, Snow, RJ, Condo, D, Snipe, R, Wadley, GD, Carr, AJ
International journal of sport nutrition and exercise metabolism. 2021;(2):168-186
Abstract
This review aimed to identify factors associated with (a) physiological responses, (b) gastrointestinal (GI) symptoms, and (c) exercise performance following sodium citrate supplementation. A literature search identified 33 articles. Observations of physiological responses and GI symptoms were categorized by dose (< 500, 500, and > 500 mg/kg body mass [BM]) and by timing of postingestion measurements (in minutes). Exercise performance following sodium citrate supplementation was compared with placebo using statistical significance, percentage change, and effect size. Performance observations were categorized by exercise duration (very short < 60 s, short ≥ 60 and ≤ 420 s, and longer > 420 s) and intensity (very high > 100% VO2max and high 90-100% VO2max). Ingestion of 500 mg/kg BM sodium citrate induced blood alkalosis more frequently than < 500 mg/kg BM, and with similar frequency to >500 mg/kg BM. The GI symptoms were minimized when a 500 mg/kg BM dose was ingested in capsules rather than in solution. Significant improvements in performance following sodium citrate supplementation were reported in all observations of short-duration and very high-intensity exercise with a 500 mg/kg BM dose. However, the efficacy of supplementation for short-duration, high-intensity exercise is less clear, given that only 25% of observations reported significant improvements in performance following sodium citrate supplementation. Based on the current literature, the authors recommend ingestion of 500 mg/kg BM sodium citrate in capsules to induce alkalosis and minimize GI symptoms. Supplementation was of most benefit to performance of short-duration exercise of very high intensity; further investigation is required to determine the importance of ingestion duration and timing.
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Protein Requirements of Pre-Menopausal Female Athletes: Systematic Literature Review.
Mercer, D, Convit, L, Condo, D, Carr, AJ, Hamilton, DL, Slater, G, Snipe, RMJ
Nutrients. 2020;(11)
Abstract
This systematic literature review aimed to determine the protein requirements of pre-menopausal (e.g., 18-45 years) female athletes and identify if the menstrual cycle phase and/or hormonal contraceptive use influence protein requirements. Four databases were searched for original research containing pre-menopausal female athletes that ingested protein alongside exercise. The Academy of Nutrition and Dietetics Quality Criteria Checklist was used to determine study quality. Fourteen studies, which included 204 recreationally active or competitive females, met the eligibility criteria for inclusion in this review, and all were assessed as positive quality. The estimated average requirement (EAR) for protein intake of pre-menopausal recreational and/or competitive female athletes is similar for those undertaking aerobic endurance (1.28-1.63 g/kg/day), resistance (1.49 g/kg/day) and intermittent exercise (1.41 g/kg/day) of ~60-90 min duration. The optimal acute protein intake and influence of menstrual cycle phase or hormonal contraceptive use on protein requirements could not be determined. However, pre- and post-exercise protein intakes of 0.32-0.38 g/kg have demonstrated beneficial physiological responses in recreational and competitive female athletes completing resistance and intermittent exercise. The protein requirements outlined in this review can be used for planning and assessing protein intakes of recreational and competitive pre-menopausal female athletes.
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Sodium citrate ingestion protocol impacts induced alkalosis, gastrointestinal symptoms, and palatability.
Urwin, CS, Snow, RJ, Orellana, L, Condo, D, Wadley, GD, Carr, AJ
Physiological reports. 2019;(19):e14216
Abstract
To compare the effect of 500 mg·kg-1 body mass (BM) sodium citrate ingested in solution or capsules on induced alkalosis, gastrointestinal symptoms and palatability. Twenty-four healthy and active participants completed two testing sessions, ingesting 500 mg·kg-1 BM sodium citrate within solution or capsules. Capillary blood samples were collected pre-ingestion, and every 30-min for 240-min post-ingestion; samples were analyzed for blood pH and [HCO3- ]. A validated questionnaire was used to quantify gastrointestinal symptoms at the same 30-min intervals. Palatability was quantified immediately after ingestion using a validated scale. There was a greater peak and change from baseline for capsules versus solution for blood pH (P < 0.001) and [HCO3- ] (P = 0.013). Blood pH and [HCO3- ] time to peak was 199 and 204 min, respectively, after capsule ingestion, both significantly later than after solution (P = 0.034, P = 0.001). Gastrointestinal symptoms were significantly elevated above baseline for both ingestion modes at each time point between 30 and 120 min after ingestion (P = 0.003), with no differences between modes at any time point (P = 0.644). Capsules were significantly more palatable than solution (P < 0.001). We recommend 500 mg·kg-1 BM sodium citrate ingestion in capsules, at least 200 min before exercise, to achieve greater alkalosis, minimize gastrointestinal symptoms, and maximize.
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Chronic Ketogenic Low Carbohydrate High Fat Diet Has Minimal Effects on Acid-Base Status in Elite Athletes.
Carr, AJ, Sharma, AP, Ross, ML, Welvaert, M, Slater, GJ, Burke, LM
Nutrients. 2018;10(2)
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The low-fat, high-carbohydrate ketogenic diet has recently been applied to the context of elite athletes to observe potential impact on performance and metabolism during exercise and rest. The aim to this study was to assess the effect of a long-term ketogenic diet on the acid-base status in elite athletes, particularly investigating whether sustained diet change caused alterations in overall acid production. Twenty-one athletes were assigned to a high carbohydrate diet, low carbohydrate diet and periodised carbohydrate availability diet for three sustained weeks. Acid-base balance was measured via blood samples at baseline and post-intervention. The main finding of this study was that a sustained ketogenic diet had no influence of acid-base status. Based on these results, the authors conclude that long-term manipulation of macronutrient intake is unlikely to influence acid-base status in this population. It is also noted that elite athletes may have an increased buffering capacity compared with the general population, and that further research should be done in different participant populations.
Abstract
Although short (up to 3 days) exposure to major shifts in macronutrient intake appears to alter acid-base status, the effects of sustained (>1 week) interventions in elite athletes has not been determined. Using a non-randomized, parallel design, we examined the effect of adaptations to 21 days of a ketogenic low carbohydrate high fat (LCHF) or periodized carbohydrate (PCHO) diet on pre- and post-exercise blood pH, and concentrations of bicarbonate (HCO₃-) and lactate (La-) in comparison to a high carbohydrate (HCHO) control. Twenty-four (17 male and 7 female) elite-level race walkers completed 21 days of either LCHF (n = 9), PCHO (n = 7), or HCHO (n = 8) under controlled diet and training conditions. At baseline and post-intervention, blood pH, blood [HCO₃-], and blood [La-] were measured before and after a graded exercise test. Net endogenous acid production (NEAP) over the previous 48-72 h was also calculated from monitored dietary intake. LCHF was not associated with significant differences in blood pH, [HCO₃-], or [La-], compared with the HCHO diet pre- or post-exercise, despite a significantly higher NEAP (mEq·day-1) (95% CI = [10.44; 36.04]). Our results indicate that chronic dietary interventions are unlikely to influence acid-base status in elite athletes, which may be due to pre-existing training adaptations, such as an enhanced buffering capacity, or the actions of respiratory and renal pathways, which have a greater influence on regulation of acid-base status than nutritional intake.
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Induced Alkalosis and Gastrointestinal Symptoms After Sodium Citrate Ingestion: a Dose-Response Investigation.
Urwin, CS, Dwyer, DB, Carr, AJ
International journal of sport nutrition and exercise metabolism. 2016;(6):542-548
Abstract
Sodium citrate induces alkalosis and can provide a performance benefit in high-intensity exercise. Previous investigations have been inconsistent in the ingestion protocols used, in particular the dose and timing of ingestion before the onset of exercise. The primary aim of the current study was to quantify blood pH, blood bicarbonate concentration and gastrointestinal symptoms after ingestion of three doses of sodium citrate (500 mg⋅kg-1, 700 mg⋅kg-1 and 900 mg⋅kg-1). Thirteen participants completed four experimental sessions, each consisting of a different dose of sodium citrate or a taste-matched placebo solution. Blood pH and blood bicarbonate concentration were measured at 30-min intervals via analysis of capillary blood samples. Gastrointestinal symptoms were also monitored at 30-min intervals. Statistical significance was accepted at a level of p < .05. Both measures of alkalosis were significantly greater after ingestion of sodium citrate compared with placebo (p < .001). No significant differences in alkalosis were found between the three sodium citrate doses (p > .05). Peak alkalosis following sodium citrate ingestion ranged from 180 to 212 min after ingestion. Gastrointestinal symptoms were significantly higher after sodium citrate ingestion compared with placebo (p < .001), while the 900 mg.kg-1 dose elicited significantly greater gastrointestinal distress than 500 mg⋅kg-1 (p = .004). It is recommended that a dose of 500 mg⋅kg-1 of sodium citrate should be ingested at least 3 hr before exercise, to achieve peak alkalosis and to minimize gastrointestinal symptoms before and during exercise.