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Ironman triathlons are ultra-endurance events of extreme duration. The performance level of those competing varies dramatically, with elite competitors finishing in ~ 8:00:00, and lower performing amateurs finishing in ~ 14-15:00:00. When applying appropriate values for swimming, cycling and running economies to these performance times, it is demonstrated that the absolute energy cost of these events is high, and the rate of energy expenditure increases in proportion with the athlete's competitive level. Given the finite human capacity for endogenous carbohydrate storage, minimising the endogenous carbohydrate cost associated with performing exercise at competitive intensities should be a goal of Ironman preparation. A range of strategies exist that may help to achieve this goal, including, but not limited to, adoption of a low-carbohydrate diet, exogenous carbohydrate supplementation and periodised training with low carbohydrate availability. Given the diverse metabolic stimuli evoked by Ironman triathlons at different performance levels, it is proposed that the performance level of the Ironman triathlete is considered when adopting metabolic strategies to minimise the endogenous carbohydrate cost associated with exercise at competitive intensities. Specifically, periodised training with low carbohydrate availability combined with exogenous carbohydrate supplementation during competition might be most appropriate for elite and top-amateur Ironman triathletes who elicit very high rates of energy expenditure. Conversely, the adoption of a low-carbohydrate or ketogenic diet might be appropriate for some lower performance amateurs (> 12 h), in whom associated high rates of fat oxidation may be almost completely sufficient to match the energy demands required.
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... Furthermore, an impaired vasomotor and sudomotor function from the lesion level downwards causes a blunted thermoregulation that may further burden cardiovascular responses, particularly in hot and humid conditions [15][16][17]. Such conditions may also bear a challenge in terms of energy supply, as higher environmental temperatures increase the dependence on CHO during exercise [21,22]. ...
... Considering the physiological demands of endurance events, CHO and fat represent the main substrates oxidized throughout prolonged endurance exercise [19,22,54,55]. The higher the exercise intensity, the greater the reliance on CHO metabolism with a concomitant downregulation of fat oxidation [7,11,19,22,56]. ...
... Considering the physiological demands of endurance events, CHO and fat represent the main substrates oxidized throughout prolonged endurance exercise [19,22,54,55]. The higher the exercise intensity, the greater the reliance on CHO metabolism with a concomitant downregulation of fat oxidation [7,11,19,22,56]. Other critical determinants are exercise duration, the athlete's fitness level and nutritional status-i.e., substrate availability [54,55]. ...
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The Paralympic movement is growing in popularity, resulting in increased numbers of athletes with a spinal cord injury (SCI) competing in various sport disciplines. Athletes with an SCI require specialized recommendations to promote health and to maximize performance, as evidenced by their metabolic and physiological adaptations. Nutrition is a key factor for optimal performance; however, scientifically supported nutritional recommendations are limited. This review summarizes the current knowledge regarding the importance of carbohydrates (CHO) for health and performance in athletes with an SCI. Factors possibly affecting CHO needs, such as muscle atrophy, reduced energy expenditure, and secondary complications are analyzed comprehensively. Furthermore, a model calculation for CHO requirements during an endurance event is provided. Along with assessing the effectiveness of CHO supplementation in the athletic population with SCI, the evaluation of their CHO intake from the available research supplies background to current practices. Finally, future directions are identified. In conclusion, the direct transfer of CHO guidelines from able-bodied (AB) athletes to athletes with an SCI does not seem to be reasonable. Based on the critical role of CHOs in exercise performance, establishing recommendations for athletes with an SCI should be the overall objective for prospective research.
... Finally, the performance was less favorable under KD than controls in subjects with a higher aerobic fitness expressed by the relative VO 2 max. Such findings could be associated with higher energy expenditure during exercise performance in more trained individuals (Maunder, Kilding, and Plews 2018) and support a recently proposed theoretical model (Maunder, Kilding, and Plews 2018) and previous meta-analysis results (Erlenbusch et al. 2005). It is important to note that modifying effects are not too large and show some imprecision; nevertheless, even very small effects could be important to cyclic performances (Hopkins, Hawley, and Burke 1999). ...
... Finally, the performance was less favorable under KD than controls in subjects with a higher aerobic fitness expressed by the relative VO 2 max. Such findings could be associated with higher energy expenditure during exercise performance in more trained individuals (Maunder, Kilding, and Plews 2018) and support a recently proposed theoretical model (Maunder, Kilding, and Plews 2018) and previous meta-analysis results (Erlenbusch et al. 2005). It is important to note that modifying effects are not too large and show some imprecision; nevertheless, even very small effects could be important to cyclic performances (Hopkins, Hawley, and Burke 1999). ...
Article
This systematic review with meta-analysis aimed to determine the effects of the ketogenic diet (KD) against carbohydrate (CHO)-rich diets on physical performance and body composition in trained individuals. The MEDLINE, EMBASE, CINAHL, SPORTDiscus, and The Cochrane Library were searched. Randomized and non-randomized controlled trials in athletes/trained adults were included. Meta-analytic models were carried out using Bayesian multilevel models. Eighteen studies were included providing estimates on cyclic exercise modes and strength one-maximum repetition (1-RM) performances and for total, fat, and free-fat masses. There were more favorable effects for CHO-rich than KD on time-trial performance (mode [95% credible interval]; −3.3% [−8.5%, 1.7%]), 1-RM (−5.7% [−14.9%, 2.6%]), and free-fat mass (−0.8 [−3.4, 1.9] kg); effects were more favorable to KD on total (−2.4 [−6.2, 1.8] kg) and fat mass losses (−2.4 [−5.4, 0.2] kg). Likely modifying effects on cyclic performance were the subject’s sex and VO2max, intervention and performance durations, and mode of exercise. The intervention duration and subjects’ sex were likely to modify effects on total body mass. KD can be a useful strategy for total and fat body losses, but a small negative effect on free-fat mass was observed. KD was not suitable for enhancing strength 1-RM or high-intensity cyclic performances.
... Dietary intake studies with low-carbohydrate, high-fat diets reported enhanced wholebody fat oxidation in elite race walkers [7]. However, the observations of impaired exercise performance with low-carbohydrate, high-fat diets [7,8] may have dampened the interest of it being a popular nutritional strategy among elite ultra-endurance athletes [9,10]. In ultraendurance athletes, dietary and training practices are expected to optimize the required physiological and structural adaptations that may minimize or even discount the effectiveness of dietary supplements that may affect substrate oxidation. ...
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Physical training for ultra-endurance running provides physiological adaptations for exercise-induced substrate oxidation. We examined the effects of New Zealand blackcurrant (NZBC) extract on running-induced metabolic and physiological responses in a male amateur ultra-endurance runner (age: 40 years, body mass: 65.9 kg, BMI: 23.1 kg·m−2, body fat: 14.7%, V˙O2max: 55.3 mL·kg−1·min−1, resting heart rate: 45 beats·min−1, running history: 6 years, marathons: 20, ultra-marathons: 28, weekly training distance: ~80 km, weekly running time: ~9 h). Indirect calorimetry was used and heart rate recorded at 15 min intervals during 120 min of treadmill running (speed: 10.5 km·h−1, 58% V˙O2max) in an environmental chamber (temperature: ~26 °C, relative humidity: ~70%) at baseline and following 7 days intake of NZBC extract (210 mg of anthocyanins·day−1) with constant monitoring of core temperature. The male runner had unlimited access to water and consumed a 100-kcal energy gel at 40- and 80 min during the 120 min run. There were no differences (mean of 8, 15 min measurements) for minute ventilation, oxygen uptake, carbon dioxide production and core temperature. With NZBC extract, the respiratory exchange ratio was 0.02 units lower, carbohydrate oxidation was 11% lower and fat oxidation was 23% higher (control: 0.39 ± 0.08, NZBC extract: 0.48 ± 0.12 g·min−1, p < 0.01). Intake of the energy gel did not abolish the enhanced fat oxidation by NZBC extract. Seven days’ intake of New Zealand blackcurrant extract altered exercise-induced substrate oxidation in a male amateur ultra-endurance runner covering a half-marathon distance in 2 h. More studies are required to address whether intake of New Zealand blackcurrant extract provides a nutritional ergogenic effect for ultra-endurance athletes to enhance exercise performance.
... The ability to effectively oxidize fat for fuel, represented by a lower RER, is important for metabolic health [14] and long-duration exercise performance [15,16], and many athletes attempt to manipulate substrate oxidation during exercise as part of a periodized nutrition and training plan [17,18]. However, managing substrate oxidation during exercise is challenged by the influence of both modifiable The easily measured and easily modifiable factors related to exercise such as exercise duration and intensity, daily macronutrient intake, and pre-and peri-exercise carbohydrate intake, can only explain roughly one-third of the variation in RER during exercise. ...
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Background: Multiple factors influence substrate oxidation during exercise including exercise duration and intensity, sex, and dietary intake before and during exercise. However, the relative influence and interaction between these factors is unclear. Objectives: Our aim was to investigate factors influencing the respiratory exchange ratio (RER) during continuous exercise and formulate multivariable regression models to determine which factors best explain RER during exercise, as well as their relative influence. Methods: Data were extracted from 434 studies reporting RER during continuous cycling exercise. General linear mixed-effect models were used to determine relationships between RER and factors purported to influence RER (e.g., exercise duration and intensity, muscle glycogen, dietary intake, age, and sex), and to examine which factors influenced RER, with standardized coefficients used to assess their relative influence. Results: The RER decreases with exercise duration, dietary fat intake, age, VO2max, and percentage of type I muscle fibers, and increases with dietary carbohydrate intake, exercise intensity, male sex, and carbohydrate intake before and during exercise. The modelling could explain up to 59% of the variation in RER, and a model using exclusively easily modified factors (exercise duration and intensity, and dietary intake before and during exercise) could only explain 36% of the variation in RER. Variables with the largest effect on RER were sex, dietary intake, and exercise duration. Among the diet-related factors, daily fat and carbohydrate intake have a larger influence than carbohydrate ingestion during exercise. Conclusion: Variability in RER during exercise cannot be fully accounted for by models incorporating a range of participant, diet, exercise, and physiological characteristics. To better understand what influences substrate oxidation during exercise further research is required on older subjects and females, and on other factors that could explain additional variability in RER.
... Relationships between fat oxidation and endurance performance have been proposed, but not well established in original research (Maunder et al. 2018a). One laboratorybased study in which dietary macronutrient composition was manipulated indicated a possible influence of PFO on 100-km cycling time-trial performance, though this was not statistically significant (Rowlands and Hopkins 2002). ...
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Purpose Whole-body fat oxidation during exercise can be measured non-invasively during athlete profiling. Gaps in understanding exist in the relationships between fat oxidation during incremental fasted exercise and skeletal muscle parameters, endurance performance, and fat oxidation during prolonged fed-state exercise. Methods Seventeen endurance-trained males underwent a (i) fasted, incremental cycling test to assess peak whole-body fat oxidation (PFO), (ii) resting vastus lateralis microbiopsy, and (iii) 30-min maximal-effort cycling time-trial preceded by 2-h of fed-state moderate-intensity cycling to assess endurance performance and fed-state metabolism on separate occasions within one week. Results PFO (0.58 ± 0.28 g.min⁻¹) was associated with vastus lateralis citrate synthase activity (69.2 ± 26.0 μmol.min−1.g⁻¹ muscle protein, r = 0.84, 95% CI 0.58, 0.95, P < 0.001), CD36 abundance (16.8 ± 12.6 μg.g⁻¹ muscle protein, rs = 0.68, 95% CI 0.31, 1.10, P = 0.01), pre-loaded 30-min time-trial performance (251 ± 51 W, r = 0.76, 95% CI 0.40, 0.91, P = 0.001; 3.2 ± 0.6 W.kg⁻¹, r = 0.62, 95% CI 0.16, 0.86, P = 0.01), and fat oxidation during prolonged fed-state cycling (r = 0.83, 95% CI 0.57, 0.94, P < 0.001). Addition of PFO to a traditional model of endurance (peak oxygen uptake, power at 4 mmol.L⁻¹ blood lactate concentration, and gross efficiency) explained an additional ~ 2.6% of variation in 30-min time-trial performance (adjusted R² = 0.903 vs. 0.877). Conclusion These associations suggest non-invasive measures of whole-body fat oxidation during exercise may be useful in the physiological profiling of endurance athletes.
... Para la valoración de la calidad de los estudios, se utiliza la escala PEDro. Esta escala está basada en la lista Delphi desarrollada por Verhagen et al. (43). La lista Delphi es una serie de criterios para la evaluación de los estudios que se incluyen en las revisiones sistemáticas. ...
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Introducción: Las estrategias nutricionales agudas consisten en pautas específicas de alimentación para llevar a cabo antes de un esfuerzo físico con el objetivo de mejorar el rendimiento del deportista. Su uso es habitual en deportes de resistencia, pero no hay revisiones sistemáticas identificando los beneficios de las estrategias nutricionales agudas publicados en los últimos años. Objetivo: El objetivo de esta revisión sistemática fue determinar las estrategias nutricionales agudas más importantes para mejorar el rendimiento en deportes de resistencia en deportistas entrenados que se han testeado en la literatura científica recientemente. Metodología: Esta revisión se realizó siguiendo los principios de PRISMA. La búsqueda bibliográfica se realizó en las bases de datos Pubmed y Web of Science. Se buscaron estudios de intervención utilizando alguna estrategia nutricional aguda en deportistas de resistencia. Los artículos escritos en idiomas distintos a español o inglés, en participantes no entrenados, en animales, o que no estuvieran publicados en los últimos 5 años fueron excluidos. Resultados: Se identificaron 87 estudios, de los cuales 11 se incluyeron tras cumplir los criterios de elegibilidad. En estos estudios hemos identificado 8 estrategias nutricionales agudas publicadas en los últimos 5 años. La ingesta aguda de cafeína, así como la ingesta de glutamina o glutamina y carbohidratos antes de la competición mejoraron el rendimiento en pruebas aeróbicas. La ingesta post ejercicio, tanto de proteínas como proteínas y carbohidratos, mejora el rendimiento y la recuperación. Por otro lado, no se observaron mejoras en el rendimiento tras ingerir nitratos en forma de gel, o aceite de oliva. Conclusiones: La ingesta aguda de cafeína, glutamina (combinada o no con carbohidratos) mejoran el rendimiento de los deportistas en pruebas aeróbicas. Por otro lado, se recomienda la ingesta de proteínas (combinadas o no con carbohidratos) para obtener mejoras en rendimiento y en capacidad de recuperación.
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Ketogenic diets and orally administered exogenous ketone supplements are strategies to increase serum ketone bodies serving as an alternative energy fuel for high energy demanding tissues, such as the brain, muscles, and the heart. The ketogenic diet is a low-carbohydrate and fat-rich diet, whereas ketone supplements are usually supplied as esters or salts. Nutritional ketosis, defined as serum ketone concentrations of ≥ 0.5 mmol/L, has a fasting-like effect and results in all sorts of metabolic shifts and thereby enhancing the health status. In this review, we thus discuss the different interventions to reach nutritional ketosis, and summarize the effects on heart diseases, epilepsy, mitochondrial diseases, and neurodegenerative disorders. Interest in the proposed therapeutic benefits of nutritional ketosis has been growing the past recent years. The implication of this nutritional intervention is becoming more evident and has shown interesting potential. Mechanistic insights explaining the overall health effects of the ketogenic state, will lead to precision nutrition for the latter diseases.
Chapter
The Ironman triathlon is a multi-sport event consisting of 3.8 km swimming, 180 km cycling, and 42.195 km running performed in this sequence. The order of the disciplines has an impact on the performance in the running split (i.e., the marathon). The cycling split seems to be the Ironman triathlon discipline that most improved overall race times during the last years and is also the discipline with the greatest influence on the overall race time of elite men and women in the Ironman World Championship, the “Ironman Hawaii.” Regarding race tactics in an Ironman triathlon, athletes should focus on saving energy during swimming and cycling for the running split (i.e., the marathon). In order to achieve the optimum performance in an Ironman triathlon, the athlete should specifically prepare for the race regarding training, mental preparation, and nutrition. Also, previous experience is of importance. Anthropometric characteristics (e.g., low body fat) are important for overall race time and the marathon split, especially in male Ironman triathletes. Individual marathon time is important for a fast Ironman race time and a faster running split.
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This study aimed to determine the effects of consuming a high fat solution (HFS) compared to a high carbohydrate solution (HCS) during a cycling effort on substrate oxidation, muscle oxygenation and performance with cyclists and triathletes. Thirteen men participated in this study (age: 30.4 ± 6.3 y; height: 178.7 ± 6.1 cm; weight: 74.9 ± 6.5 kg; V̇O2 peak: 60.5 ± 7.9 mlO2×kg-1×min-1). The solutions were isocaloric (total of 720 kcal) and were consumed every 20 minutes. Each solution of HFS contained 12.78 g of lipids, 1.33 g of carbohydrates and 0.67 g of proteins, and each solution of HCS contained 28 g of carbohydrates. We measured pulmonary oxygen consumption and skeletal muscle oxygenation, using a Near Infrared Spectrometer (NIRS) during a cycling effort consisting of 2 hours at 65 % of maximal aerobic power (MAP) followed immediately by a 3-minute time-trial (TT). We observed that the consumption of the HFS increased the rate of fat oxidation at the end of the sub-maximal effort (0.61 ± 0.14 vs 0.53 ± 0.17 g×min-1, p < 0.05). We have also shown that the HFS negatively affected the performance in the TT (mean Watts: HCS: 347.0 ± 77.4 vs HFS: 326.5 ± 88.8 W; p < 0.05) and the rating of perceived exertions during the sub-maximal effort (modified Borg Perceived Exertion scale: 1–10) (mean: 3.62 ± 0.58 for HCS vs 4.16 ± 0.62 for HFS; p < 0.05). We did not observe a significant effect of the acute consumption of the HFS compared to the HCS on muscle oxygenation during the cycling effort. Finally, we observed that cyclists who demonstrated a high skeletal muscle deoxygenation relative to their pulmonary oxygen consumption (DHHb/V̇O2) had a higher fat oxidation capacity (higher Fatmax). In conclusion, even though the consumption of HFS increased the rate of fat oxidation at the end of a sub-maximal effort, it did not affect muscle oxygenation and it negatively affected performance and perceived exertion during a time-trial and caused gastro-intestinal distress in some participants. Keywords: Fat oxidation, Skeletal muscle oxygenation, Lipid supplementation, Carbohydrate supplementation, Near Infrared Spectroscopy (NIRS), Cycling, Triathlon.
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Deliberately training with reduced carbohydrate (CHO) availability to enhance endurance-training-induced metabolic adaptations of skeletal muscle (i.e. the ‘train low, compete high’ paradigm) is a hot topic within sport nutrition. Train-low studies involve periodically training (e.g., 30–50% of training sessions) with reduced CHO availability, where train-low models include twice per day training, fasted training, post-exercise CHO restriction and ‘sleep low, train low’. When compared with high CHO availability, data suggest that augmented cell signalling (73% of 11 studies), gene expression (75% of 12 studies) and training-induced increases in oxidative enzyme activity/protein content (78% of 9 studies) associated with ‘train low’ are especially apparent when training sessions are commenced within a specific range of muscle glycogen concentrations. Nonetheless, such muscle adaptations do not always translate to improved exercise performance (e.g. 37 and 63% of 11 studies show improvements or no change, respectively). Herein, we present our rationale for the glycogen threshold hypothesis, a window of muscle glycogen concentrations that simultaneously permits completion of required training workloads and activation of the molecular machinery regulating training adaptations. We also present the ‘fuel for the work required’ paradigm (representative of an amalgamation of train-low models) whereby CHO availability is adjusted in accordance with the demands of the upcoming training session(s). In order to strategically implement train-low sessions, our challenge now is to quantify the glycogen cost of habitual training sessions (so as to inform the attainment of any potential threshold) and ensure absolute training intensity is not compromised, while also creating a metabolic milieu conducive to facilitating the endurance phenotype.
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The gastrointestinal (GI) tract plays a critical role in delivering carbohydrate and fluid during prolonged exercise and can therefore be a major determinant of performance. The incidence of GI problems in athletes participating in endurance events is high, indicating that GI function is not always optimal in those conditions. A substantial body of evidence suggests that the GI system is highly adaptable. Gastric emptying as well as stomach comfort can be “trained” and perceptions of fullness decreased; some studies have suggested that nutrient-specific increases in gastric emptying may occur. Evidence also shows that diet has an impact on the capacity of the intestine to absorb nutrients. Again, the adaptations that occur appear to be nutrient specific. For example, a high-carbohydrate diet will increase the density of sodium-dependent glucose-1 (SGLT1) transporters in the intestine as well as the activity of the transporter, allowing greater carbohydrate absorption and oxidation during exercise. It is also likely that, when such adaptations occur, the chances of developing GI distress are smaller. Future studies should include more human studies and focus on a number of areas, including the most effective methods to induce gut adaptations and the timeline of adaptations. To develop effective strategies, a better understanding of the exact mechanisms underlying these adaptations is important. It is clear that “nutritional training” can improve gastric emptying and absorption and likely reduce the chances and/or severity of GI problems, thereby improving endurance performance as well as providing a better experience for the athlete. The gut is an important organ for endurance athletes and should be trained for the conditions in which it will be required to function.
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Carbohydrate and fat are the main substrates utilized during prolonged endurance-type exercise. The relative contribution of each is primarily determined by the intensity and duration of exercise, along with individual training and nutritional status. During moderate-to-high intensity exercise, carbohydrate represents the main substrate source. As endogenous carbohydrate stores (primarily in liver and muscle) are relatively small, endurance-type exercise performance/capacity is often limited by endogenous carbohydrate availability. Much exercise metabolism research to date has focused on muscle glycogen utilization with little attention to the contribution of liver glycogen. 13C magnetic resonance spectroscopy permits direct, non-invasive measurements of liver glycogen content and has increased understanding of the relevance of liver glycogen during exercise. In contrast to muscle, endurance-trained athletes do not exhibit elevated basal liver glycogen concentrations. However, there is evidence that liver glycogenolysis may be lower in endurance-trained athletes compared to untrained controls during moderate-to-high intensity exercise. Liver glycogen sparing in an endurance-trained state may therefore partly account for training-induced performance/capacity adaptations during prolonged (>90 min) exercise. Ingestion of carbohydrate at a relatively high rate (>1.5 g/min) can prevent liver glycogen depletion during moderate-intensity exercise, independent of the type of carbohydrate (e.g. glucose vs sucrose) ingested. To minimize gastrointestinal discomfort, it is recommended to ingest specific combinations or types of carbohydrates (glucose plus fructose and/or sucrose). By co-ingesting glucose with either galactose or fructose, post-exercise liver glycogen repletion rates can be doubled. There are currently no guidelines for carbohydrate ingestion to maximize liver glycogen repletion.
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The aim of the present study was to investigate the relationship between maximal fat oxidation rate (MFO) measured during a progressive exercise test on a cycle ergometer and ultra-endurance performance. 61 male ironman athletes (age: 35±1 yrs. [23–47 yrs.], with a BMI of 23.6±0.3 kg/m2 [20.0–30.1 kg/m2], a body fat percentage of 16.7±0.7% [8.4–30.7%] and a VO2peak of 58.7±0.7 ml/min/kg [43.9–72.5 ml/min/kg] SEM [Range]) were tested in the laboratory between 25 and 4 days prior to the ultra-endurance event, 2016 Ironman Copenhagen. Simple bivariate analyses revealed significant negative correlations between race time and MFO (r2=0.12, p<0.005) and VO2peak (r2=0.45, p<0.0001) and a positive correlation between race time and body fat percentage (r2=0.27, p<0.0001). MFO and VO2peak were not correlated. When the significant variables from the bivariate regression analyses were entered into the multiple regression models, VO2peak and MFO together explained 50% of the variation observed in race time among the 61 Ironman athletes (adj R2=0.50, p<0.001). These results suggests that maximal fat oxidation rate exert an independent influence on ultra-endurance performance (>9 h). Furthermore, we demonstrate that 50% of the variation in Ironman triathlon race time can be explained by peak oxygen uptake and maximal fat oxidation.
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Background: Due to gastrointestinal tract adaptability, the study aimed to determine the impact of two weeks gut-training protocol over two weeks on gastrointestinal status, blood glucose availability, fuel kinetics, and running performance. Methods: Endurance runners (n= 25) performed a gut-challenge trial (GC1), comprising of 2 h running exercise at 60% VO2max whilst consuming gel-discs containing 30 g carbohydrates (2:1 glucose-fructose, 10% w/v) every 20 min, and a 1 h distance test. Participants were then randomly assigned to a carbohydrate gel-disc (CHO-S), carbohydrate food (CHO-F), or placebo (PLA) gut-training group for a two weeks repetitive gut-challenge intervention. Participants then repeated a second gut-challenge trial (GC2). Results: Gastrointestinal symptoms reduced in GC2 on CHO-S (60%; p= 0.008) and CHO-F (63%; p= 0.046); reductions were greater than PLA (p< 0.05). H2 peak was lower in GC2 on CHO-S (mean (CI): 6 (4-8) ppm) compared with CHO-F (9 (6-12) ppm) and PLA (12 (2-21) ppm) (trial*time: p< 0.001). Blood glucose concentration was higher in GC2 on CHO-S (7.2 (6.3-8.1) mMol·L-1) compared with CHO-F (6.1 (5.7-6.5) mMol·L-1) and PLA (6.2 (4.9-7.5) mMol·L-1) (trial*time: p= 0.015). No difference in oxidation rates, plasma I-FABP and cortisol concentrations were observed between groups and trials. Distance test improved on CHO-S (5.2%) and CHO-F (4.3%) in GC2, but not on PLA (-2.1%) (trial*time: p= 0.009). Conclusion: Two weeks of gut-training with CHO-S and CHO-F improved gastrointestinal symptoms and running performance compared with PLA. CHO-S also reduced malabsorption and increased blood glucose availability during endurance running compared with PLA.
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Introduction: This case study reports a range of physiological characteristics in a two-time Tour de France champion. Methods: After body composition assessment (dual-energy x-ray absorptiometry), two submaximal cycling step tests were performed in ambient (20°C, 40%) and hot and humid (30°C, 60% [HH]) conditions from which measures of gross efficiency (GE), lactate-power landmarks, and heart rate responses were calculated. In addition, thermoregulatory and sweat responses were collected throughout. V˙O2peak and peak power output (PPO) were also identified after a separate ramp test to exhaustion. Results: V˙O2peak and PPO were 5.91 L·min (84 mL·kg·min) and 525 W, respectively, whereas mean GE values were 23.0% and 23.6% for ambient and HH conditions, respectively. In addition to superior GE, power output at 4 mmol·L lactate was higher in HH versus ambient conditions (429.6 vs 419.0 W) supporting anecdotal reports from the participant of good performance in the heat. Peak core and skin temperature, sweat rate, and electrolyte content were higher in HH conditions. Body fat percentage was 9.5%, whereas total fat mass, lean mass, and bone mineral content were 6.7, 61.5, and 2.8 kg, respectively. Conclusion: The aerobic physiology and PPO values indentified are among the highest reported for professional road cyclists. Notably, the participant displayed both a high V˙O2peak and GE, which is uncommon among elite cyclists and may be a contributing factor to their success in elite cycling. In addition, performance in HH conditions was strong, suggesting effective thermoregulatory physiology. In summary, this is the first study to report physiological characteristics of a multiple Tour de France champion in close to peak condition and suggests what may be the prerequisite physiological and thermoregulatory capacities for success at this level.
Article
Ketosis, the metabolic response to energy crisis, is a mechanism to sustain life by altering oxidative fuel selection. Often overlooked for its metabolic potential, ketosis is poorly understood outside of starvation or diabetic crisis. Thus, we studied the biochemical advantages of ketosis in humans using a ketone ester-based form of nutrition without the unwanted milieu of endogenous ketone body production by caloric or carbohydrate restriction. In five separate studies of 39 high-performance athletes, we show how this unique metabolic state improves physical endurance by altering fuel competition for oxidative respiration. Ketosis decreased muscle glycolysis and plasma lactate concentrations, while providing an alternative substrate for oxidative phosphorylation. Ketosis increased intramuscular triacylglycerol oxidation during exercise, even in the presence of normal muscle glycogen, co-ingested carbohydrate and elevated insulin. These findings may hold clues to greater human potential and a better understanding of fuel metabolism in health and disease.