Carbohydrate feeding during exercise

Carbohydrate Oral Rinsing, Cycling Performance and Individual Complex Carbohydrate Taste Sensitivity

The aim of this pilot study was to determine the effect of individual complex carbohydrate taste sensitivity on cycling performance with complex carbohydrate oral rinsing. Ten male participants completed five cycling time trials in a fasted state with a seven-day washout period between each trial. Participants completed a fixed amount of work (738.45 ± 150.74 kJ) as fast as possible on a cycle ergometer while rinsing with an oral rinse for 10 s every 12.5% of the trial. An oral rinse (maltodextrin, oligofructose, glucose, sucralose or water control) was given per visit in a randomised, crossover, blinded design. Afterwards, participants had their taste assessed with three stimuli, complex carbohydrate (maltodextrin), sweet (glucose) and sour (citric acid), using taste assessment protocol to determine individual taste sensitivity status. Participants were subsequently grouped according to their complex carbohydrate taste sensitivity and complex carbohydrate taste intensity. There were no significant effects of the oral rinses on cycling performance time (p = 0.173). Participants who did not have improvements in exercise performance with the maltodextrin rinse experienced a stronger taste intensity with complex carbohydrate stimuli at baseline (p = 0.047) and overall (p = 0.047) than those who did have improvements in performance. Overall, a carbohydrate oral rinse was ineffective in significantly improving cycling performance in comparison with a water control. However, when participants were grouped according to complex carbohydrate taste intensity, differences in exercise performance suggest that individual sensitivity status to complex carbohydrates could impact the efficacy of a carbohydrate-based oral rinse.

Effects of carbohydrate drinks ingestion on executive function in athletes: a systematic review and meta-analysis

Background

Carbohydrates are often used as boosters for endurance and high-intensity exercise. However, it is unclear whether carbohydrate drinks intake before or during exercise can affect specific domains of cognitive function, such as Executive Function (EF).

Methods

Following the guidance of PRISMA 2020, we searched six major databases including PubMed, WOS, SPORTDiscus, Cochrane, Embase, and Scopus. Outcomes were presented in the form of Reaction Time (RT), Accuracy (ACC), and Scores (Score) for performing EF tests. Effect sizes were calculated from the test results of EF and expressed as standardized mean differences (SMDs). After analyzing the overall results, we performed subgroup analyses based on the athletes' program characteristics.

Results

After retrieving a total of 5,355 articles, ten randomized controlled trials (RCTs) were identified and included in this review. The overall results showed that the intake of carbohydrate drinks before or during exercise did not have a significant effect on the reduction of EF after exercise (ACC (-0.05 [-0.27, 0.18]); RT (-0.18 [-0.45, 0.09]); Score (0.24 [-0.20, 0.68])). The subgroup analyses based on open skill sports and close skill sports also showed invalid results, but the results of RT ended up with different preference (ACC of open skill sports athletes (-0.10 [-0.34, 0.14]); RT of open skill athletes (-0.27 [-0.60, 0.07]); RT of close skill athletes (0.29 [-0.24, 0.82])).

Conclusion

The intake of 6-12% of single or mixed carbohydrates before or during exercise was not significantly effective in reducing the decline in EF after exercise. Our findings may have been influenced by the type of intervention, dose, mode of administration, or individual variability of the included subjects.

Influence of Exogenous Factors Related to Nutritional and Hydration Strategies and Environmental Conditions on Fatigue in Endurance Sports: A Systematic Review with Meta-Analysis

The aim of this systematic review with meta-analysis was to examine the influence of exogenous factors related to nutritional and hydration strategies and environmental conditions, as modulators of fatigue, including factors associated with performance fatigability and perceived fatigability, in endurance tests lasting 45 min to 3 h. A search was carried out using four databases: PubMed, Web of Science, SPORTDiscus, and EBSCO. A total of 5103 articles were screened, with 34 included in the meta-analysis. The review was registered with PROSPERO (CRD42022327203) and adhered to the PRISMA guidelines. The study quality was evaluated according to the PEDro score and assessed using Rosenthal's fail-safe N. Carbohydrate (CHO) intake increased the time to exhaustion (p < 0.001) and decreased the heart rate (HR) during the test (p = 0.018). Carbohydrate with protein intake (CHO + PROT) increased lactate during the test (p = 0.039). With respect to hydration, dehydrated individuals showed a higher rate of perceived exertion (RPE) (p = 0.016) and had a higher body mass loss (p = 0.018). In hot conditions, athletes showed significant increases in RPE (p < 0.001), HR (p < 0.001), and skin temperature (p = 0.002), and a decrease in the temperature gradient (p < 0.001) after the test. No differences were found when athletes were subjected to altitude or cold conditions. In conclusion, the results revealed that exogenous factors, such as nutritional and hydration strategies, as well as environmental conditions, affected fatigue in endurance sports, including factors associated with performance fatigability and perceived fatigability.

Maltodextrin-Based Carbohydrate Oral Rinsing and Exercise Performance: Systematic Review and Meta-Analysis

Background

Carbohydrates are an important fuel for optimal exercise performance during moderate- and high-intensity exercise; however, carbohydrate ingestion during high-intensity exercise may cause gastrointestinal upset. A carbohydrate oral rinse is an alternative method to improve exercise performance in moderate- to high-intensity exercise with a duration of 30–75 min. This is the first systematic review and meta-analysis to comprehensively examine the isolated effect of maltodextrin-based rinsing on exercise performance.

Objective

The objective of this review was to establish the effect of a maltodextrin-based carbohydrate oral rinse on exercise performance across various modes of exercise. Furthermore, a secondary objective was to determine the effects of moderators [(1) participant characteristics; (2) oral rinse protocols; (3) exercise protocol (i.e. cycling, running etc.) and (4) fasting] on exercise performance while using a maltodextrin-based, carbohydrate oral rinse.

Methods

Five databases (MEDLINE, PsycINFO, Embase, SPORTDiscus and Global Health) were systematically searched for articles up to March 2021 and screened using Covidence (a systematic review management tool). A random effects robust meta-analysis and subgroup analyses were performed using Stata Statistical Software: Release 16.

Results

Thirty-five articles met the inclusion criteria and were included in the systematic review; 34 of these articles were included in the meta-analysis. When using a conventional meta-analytic approach, overall, a carbohydrate oral rinse improved exercise performance in comparison with a placebo (SMD = 0.15, 95% CI 0.04, 0.27; p = 0.01). Furthermore, when implementing an adjusted, conservative, random effects meta-regression model using robust variance estimation, overall, compared with placebo, a carbohydrate oral rinse demonstrated evidence of improving exercise performance with a small effect size (SMD = 0.17, 95% CI − 0.01, 0.34; p = 0.051).

Conclusion

This systematic review and meta-analysis demonstrates that a maltodextrin-based carbohydrate oral rinse can improve exercise performance. When comparing the two meta-analytic approaches, although non-significant, the more robust, adjusted, random effects meta-regression model demonstrated some evidence of a maltodextrin-based carbohydrate oral rinse improving exercise performance overall.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-022-01658-3.

The Impact of Sodium Alginate Hydrogel on Exogenous Glucose Oxidation Rate and Gastrointestinal Comfort in Well-Trained Runners

Purpose

The purpose of this study is to quantify the effect of adding sodium alginate and pectin to a carbohydrate (CHO) beverage on exogenous glucose (ExGluc) oxidation rate compared with an isocaloric CHO beverage.

Methods

Following familiarization, eight well-trained endurance athletes performed four bouts of prolonged running (105 min; 71 ± 4% of VO₂max) while ingesting 175 mL of one of the experimental beverages every 15 min. In randomized order, participants consumed either 70 g^.h⁻¹ of maltodextrin and fructose (10% CHO; NORM), 70 g^.h⁻¹ of maltodextrin, fructose, sodium alginate, and pectin (10% CHO; ENCAP), 180 g^.h⁻¹ of maltodextrin, fructose, sodium alginate, and pectin (26% CHO; HiENCAP), or water (WAT). All CHO beverages had a maltodextrin:fructose ratio of 1:0.7 and contained 1.5 g^.L⁻¹ of sodium chloride. Total substrate oxidation, ExGluc oxidation rate, blood glucose, blood lactate, serum non-esterified fatty acid (NEFA) concentration, and RPE were measured for every 15 min. Every 30 min participants provided information regarding their gastrointestinal discomfort (GID).

Results

There was no significant difference in peak ExGluc oxidation between NORM and ENCAP (0.63 ± 0.07 and 0.64 ± 0.11 g^.min⁻¹, respectively; p > 0.5), both of which were significantly lower than HiENCAP (1.13 ± 0.13 g^.min⁻¹, p < 0.01). Both NORM and HiENCAP demonstrated higher total CHO oxidation than WAT from 60 and 75 min, respectively, until the end of exercise, with no differences between CHO trials. During the first 60 min, blood glucose was significantly lower in WAT compared with NORM and HiENCAP, but no differences were found between CHO beverages. Both ENCAP and HiENCAP demonstrated a higher blood glucose concentration from 60–105 min than WAT, and ENCAP was significantly higher than HiENCAP. There were no significant differences in reported GID symptoms between the trials.

Conclusions

At moderate ingestion rates (i.e., 70 g^.h⁻¹), the addition of sodium alginate and pectin did not influence the ExGluc oxidation rate compared with an isocaloric CHO beverage. At very high ingestion rates (i.e., 180 g^.h⁻¹), high rates of ExGluc oxidation were achieved in line with the literature.

Meta-Analysis of Carbohydrate Solution Intake during Prolonged Exercise in Adults: From the Last 45+ Years' Perspective

Carbohydrate (CHO) supplementation during prolonged exercise postpones fatigue. However, the optimum administration timing, dosage, type of CHO intake, and possible interaction of the ergogenic effect with athletes' cardiorespiratory fitness (CRF) are not clear. Ninety-six studies (from relevant databases based on predefined eligibility criteria) were selected for meta-analysis to investigate the acute effect of ≤20% CHO solutions on prolonged exercise performance. The between-subject standardized mean difference [SMD = ([mean post-value treatment group-mean post-value control group]/pooled variance)] was assessed. Overall, SMD [95% CI] of 0.43 [0.35, 0.51] was significant (p < 0.001). Subgroup analysis showed that SMD was reduced as the subjects' CRF level increased, with a 6-8% CHO solution composed of GL:FRU improving performance (exercise: 1-4 h); administration during the event led to a superior performance compared to administration before the exercise, with a 6-8% single-source CHO solution increasing performance in intermittent and 'stop and start' sports and an ~6% CHO solution appearing beneficial for 45-60 min exercises, but there were no significant differences between subjects' gender and age groups, varied CHO concentrations, doses, or types in the effect measurement. The evidence found was sound enough to support the hypothesis that CHO solutions, when ingested during endurance exercise, have ergogenic action and a possible crossover interaction with the subject's CRF.

High Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols (FODMAP) Consumption Among Endurance Athletes and Relationship to Gastrointestinal Symptoms

Endurance athletes commonly experience lower gastrointestinal (GI) symptoms similar to those of irritable bowel syndrome (IBS). Previous research on the restriction of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP), a diet-based mitigation strategy initially developed for IBS, has shown promise for application in athlete populations. Athlete's dietary strategies surrounding exercise have not been formally assessed in relation to FODMAP content of foods or sports nutrition products. Additionally, the FODMAP content of athlete's habitual diets has not been examined in larger sample sizes. This research aims to investigate the FODMAP content of endurance athlete diets by examining these three areas, in conjunction with GI symptoms. Dietary habits surrounding exercise and GI symptoms were examined in 430 endurance athletes using a previously validated Endurance Athlete Questionnaire. A subset of athletes (n = 73) completed a FODMAP-specific food frequency questionnaire for habitual intake. The most commonly reported sports nutrition products were analyzed for FODMAP content using standardized analytical methods. Mean habitual intakes were compared to previous FODMAP studies and medians were compared between those with and without lower GI symptoms. Athletes commonly consumed high FODMAP foods during pre-race dinners and breakfasts, with over 60% reporting specific high FODMAP foods. More frequent nutrition product use, particularly solid, gel/gummy, and homemade products, was often related to increased frequency of GI symptoms. Of the sixteen commonly used sports nutrition products tested, seven were high FODMAP in one serving. All but one of the remaining products became high FODMAP when consumed in multiple servings, as is likely the case during endurance exercise. Average habitual FODMAP intake was 26.1 g (±15.9 g), similar to intakes classified as high FODMAP in previous research on FODMAPs and IBS or GI symptoms. Only 15.1% of athletes consumed a diet that would be considered low in FODMAP. Exploratory analyses showed higher intake of some FODMAP types among athletes exhibiting various lower GI symptoms. Overall, this study demonstrated that FODMAP intake by endurance athletes is high both surrounding exercise and habitually, and may be contributing to GI symptoms experienced during exercise. This information can be utilized when analyzing athlete diets and selecting foods to decrease GI symptoms.

Effects of acute nutritional ketosis during exercise in adults with glycogen storage disease type IIIa are phenotype-specific: An investigator-initiated, randomized, crossover study

Glycogen storage disease type IIIa (GSDIIIa) is an inborn error of carbohydrate metabolism caused by a debranching enzyme deficiency. A subgroup of GSDIIIa patients develops severe myopathy. The purpose of this study was to investigate whether acute nutritional ketosis (ANK) in response to ketone-ester (KE) ingestion is effective to deliver oxidative substrate to exercising muscle in GSDIIIa patients. This was an investigator-initiated, researcher-blinded, randomized, crossover study in six adult GSDIIIa patients. Prior to exercise subjects ingested a carbohydrate drink (~66 g, CHO) or a ketone-ester (395 mg/kg, KE) + carbohydrate drink (30 g, KE + CHO). Subjects performed 15-minute cycling exercise on an upright ergometer followed by 10-minute supine cycling in a magnetic resonance (MR) scanner at two submaximal workloads (30% and 60% of individual maximum, respectively). Blood metabolites, indirect calorimetry data, and in vivo ³¹ P-MR spectra from quadriceps muscle were collected during exercise. KE + CHO induced ANK in all six subjects with median peak βHB concentration of 2.6 mmol/L (range: 1.6-3.1). Subjects remained normoglycemic in both study arms, but delta glucose concentration was 2-fold lower in the KE + CHO arm. The respiratory exchange ratio did not increase in the KE + CHO arm when workload was doubled in subjects with overt myopathy. In vivo ³¹ P MR spectra showed a favorable change in quadriceps energetic state during exercise in the KE + CHO arm compared to CHO in subjects with overt myopathy. Effects of ANK during exercise are phenotype-specific in adult GSDIIIa patients. ANK presents a promising therapy in GSDIIIa patients with a severe myopathic phenotype. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier: NCT03011203.

Nitrate-rich beetroot juice offsets salivary acidity following carbohydrate ingestion before and after endurance exercise in healthy male runners

There have been recent calls for strategies to improve oral health in athletes. High carbohydrate diets, exercise induced dehydration and transient perturbations to immune function combine to increase oral disease risk in this group. We tested whether a single dose of nitrate (NO₃^-) would offset the reduction in salivary pH following carbohydrate ingestion before and after an exercise bout designed to cause mild dehydration. Eleven trained male runners (V˙O2max 53 ± 9 ml∙kg^-1∙min^-1, age 30 ± 7 years) completed a randomised placebo-controlled study comprising four experimental trials. Participants ingested the following fluids one hour before each trial: (a) 140 ml of water (negative-control), (b) 140 ml of water (positive-control), (c) 140 ml of NO₃^- rich beetroot juice (~12.4 mmol NO₃^-) (NO₃^- trial) or (d) 140 ml NO₃^- depleted beetroot juice (placebo-trial). During the negative-control trial, participants ingested 795 ml of water in three equal aliquots: before, during, and after 90 min of submaximal running. In the other trials they received 795 ml of carbohydrate supplements in the same fashion. Venous blood was collected before and after the exercise bout and saliva was sampled before and repeatedly over the 20 min following carbohydrate or water ingestion. As expected, nitrite (NO₂^-) and NO₃^- were higher in plasma and saliva during the NO₃^- trial than all other trials (all P<0.001). Compared to the negative-control, salivary-pH was significantly reduced following the ingestion of carbohydrate in the positive-control and placebo trials (both P <0.05). Salivary-pH was similar between the negative-control and NO₃^- trials before and after exercise despite ingestion of carbohydrate in the NO₃^- trial (both P≥0.221). Ingesting NO₃^- attenuates the expected reduction in salivary-pH following carbohydrate supplements and exercise-induced dehydration. NO₃^- should be considered by athletes as a novel nutritional strategy to reduce the risk of developing acidity related oral health conditions.

Carbohydrate supplementation: a critical review of recent innovations

PURPOSE

To critically examine the research on novel supplements and strategies designed to enhance carbohydrate delivery and/or availability.

METHODS

Narrative review.

RESULTS

Available data would suggest that there are varying levels of effectiveness based on the supplement/supplementation strategy in question and mechanism of action. Novel carbohydrate supplements including multiple transportable carbohydrate (MTC), modified carbohydrate (MC), and hydrogels (HGEL) have been generally effective at modifying gastric emptying and/or intestinal absorption. Moreover, these effects often correlate with altered fuel utilization patterns and/or glycogen storage. Nevertheless, performance effects differ widely based on supplement and study design. MTC consistently enhances performance, but the magnitude of the effect is yet to be fully elucidated. MC and HGEL seem unlikely to be beneficial when compared to supplementation strategies that align with current sport nutrition recommendations. Combining carbohydrate with other ergogenic substances may, in some cases, result in additive or synergistic effects on metabolism and/or performance; however, data are often lacking and results vary based on the quantity, timing, and inter-individual responses to different treatments. Altering dietary carbohydrate intake likely influences absorption, oxidation, and and/or storage of acutely ingested carbohydrate, but how this affects the ergogenicity of carbohydrate is still mostly unknown.

CONCLUSIONS

In conclusion, novel carbohydrate supplements and strategies alter carbohydrate delivery through various mechanisms. However, more research is needed to determine if/when interventions are ergogenic based on different contexts, populations, and applications.

Effect of the Glycemic Index of Meals on Physical Exercise: A Case Report

Carbohydrate uptake before physical exercise allows to maintain plasma glucose concentration. Though, foods or beverages containing the same carbohydrate concentration do not produce the same glycemic and insulin responses which are related to their glycemic index (GI). Last, most studies of CHO loading have been conducted with male subjects, with the assumption that the results also apply to female athletes.

Sixteen volunteer amateur athletes, eight men and eight women (age 39.1 ± 7.8 y; VO2max 55,7 ± 11,7 ml/kg/min), were selected and then divided into four groups of four people each one. The trial was divided into several days, one for each group. A carbohydrate source or a placebo (energy 86,5 ± 6,7 kcal; CHO 20,0 g; fat 0,3 ± 0,3 g; protein 0,8 ± 0,8 g) was assigned randomly to each athlete in the group: these supplements differed in the ability to increase blood glucose (banana: high-GI; dried apricots: low-GI; energy gel: mixture of CHO with different blood release), while the placebo was composed of water, sodium cyclamate, sodium saccharin and acesulfame potassium. Three blood samples were taken from each athlete from finger, by glucometer: one before supplementation, one half an hour later – at the start of the run – and one at the end of the exercise.

Physical activity consisted of 40 minutes run at medium-high intensity, corresponding to 82% of maximum heart rate or 70% of VO2max. In order to improve the analysis of the results obtained from the detection of biological samples, a questionnaire was submitted to all participants to know their lifestyle and anthropometric and physiological data.

Results highlighted a different glycemic response between men and women, suggesting the consumption of low-GI food rather than high-GI before physical exercise in order to keep plasma glucose levels constant.

Effects of Energy Gel Ingestion on Blood Glucose, Lactate, and Performance Measures During Prolonged Cycling

Kozlowski, KF, Ferrentino-DePriest, A, and Cerny, F. Effects of energy gel ingestion on blood glucose, lactate, and performance measures during prolonged cycling. J Strength Cond Res XX(X): 000-000, 2020-Endurance athletes have long used carbohydrate supplementation during prolonged exercise (most recently with energy gels) to enhance performance. The purpose of this study was to determine the effect of carbohydrate energy gel ingestion schedules (e.g., manufacturer's recommendations vs. a more frequent ingestion schedule) during 2 hours of steady-state cycling exercise on (a) blood glucose, (b) blood lactate, and (c) performance of a subsequent 15-minute time trial (TT). Ten trained cyclists (5 men and 5 women, mean age = 28.4 ± 3.66 years; body mass = 68.9 ± 10.63 kg; and V[Combining Dot Above]O2max = 54.57 ± 9.45 mlO2·kg·min) performed 3 exercise trials in a randomized order. One gel was ingested 15 minutes before exercise during all trials. The 3 experimental trials included gel ingestion every 30 minutes (T1), every 45 minutes (T2) during exercise, and no gel ingested during exercise (T3). Subjects cycled at 70% of V[Combining Dot Above]O2max for 2 hours, followed by a 15-minute fixed gear TT. The blood glucose level at 60 minutes of exercise was higher during T1 (125.5 ± 30.96 mg·dl) and T2 (127.6 ± 14.82 mg·dl) compared with T3 (102.8 ± 15.85 mg·dl). Time trial distance was significantly greater for T1 (7.56 ± 0.77 km) and T2 (7.16 ± 0.92 km) than T3 (6.69 ± 0.74 km) (p = 0.003) with moderate to strong effect sizes between trials. There were no differences in blood lactate concentrations across trials. Ingestion of energy gels during prolonged cycling elevates blood glucose levels and enhances subsequent performance, whereas a more frequent ingestion elicits additional performance benefits.

Nutrition for Female Soccer Players-Recommendations

Soccer is one of the most popular sports in the world. As its number of players is increasing, the number of female players is also on the rise. However, there are limited data about how the diets of female soccer players should be designed. Thus, the aim of our work is to deliver concise nutritional recommendations for women practicing this sport. Based on a literature review, we emphasize that individual adjustment of the energy value of the diet is the key factor for the physical performance of female soccer players. Appropriate macronutrient intake makes it possible to achieve the proper energy value of the diet (5-10 g/kg body mass/day carbohydrates; 1.2-1.7 g/kg body mass/day proteins; <30% fats from energy). The micronutrients should be consumed in amounts corresponding to individual values recommended in national standards. Soccer players should pay special attention to the proper consumption of such micronutrients, as well as vitamins such as iron, calcium, and vitamin D. The right amount of fluid intake, consistent with the player's needs, is crucial in maximizing exercise performance. The diet of a female practicing soccer is usually characterized with low energy values, which increases the risk of various health consequences related to low energy availability. Monitoring the diets of female soccer players is, therefore, necessary.

Nutritional strategies in an elite wheelchair marathoner at 3900 m altitude: a case report

BACKGROUND

Altitude training is a common practice among middle-distance and marathon runners. During acclimatization, sympathetic drive may increase resting metabolic rate (RMR), therefore implementation of targeted nutritional interventions based on training demands and environmental conditions becomes paramount. This single case study represents the first nutritional intervention performed under hypobaric hypoxic conditions (3900 m) in Paralympic sport. These results may elucidate the unique nutritional requirements of upper body endurance athletes training at altitude.

CASE PRESENTATION

This case study examined the effects of a nutritional intervention on the body mass of a 36-year-old professional wheelchair athlete (silver medalist at the Paralympic Games and 106 victories in assorted road events) during a five-week altitude training camp, divided into pre-altitude at sea level (B_N), acclimatization to altitude (Puno, 3860 m) (B_H), specific training (W_1,2,3,4) and return to sea level (Post) phases. Energy intake (kcal) and body mass (kg) were recorded daily. Results demonstrated significant decrease in body mass between B_N and B_H (52.6 ± 0.4 vs 50.7 ± 0.5 kg, P < 0.001) which returned to pre-altitude values, upon returning to sea level at Post (52.1 ± 0.5 kg). A greater daily intake was observed during B_H (2899 ± 670 kcal) and W_1,2,3 (3037 ± 490; 3116 ± 170; 3101 ± 385 kcal) compared to B_N (2397 ± 242 kcal, P < 0.01) and Post (2411 ± 137 kcal, P < 0.01). No differences were reported between W₄ (2786 ± 375 kcal), B_N and Post. The amount of carbohydrates ingested (g · kg^- 1) was greater in W_1,2,3, (9.6 ± 2.1; 9.9 ± 1.2; 9.6 ± 1.2) than in B_N (7.1 ± 1.2) and Post (6.3 ± 0.8, P < 0.001). Effect sizes (Cohen's d) for all variables relative to B_N (all time points) exceed a large effect (d > 0.80).

CONCLUSIONS

These results suggest an elite wheelchair marathoner training at 3860 m required increased nutrient requirements as well as the systematic control needed to re-adapt a nutritional program. Moreover, our findings highlight training and nutritional prescription optimization of elite wheelchair athletes, under challenging environmental conditions.

Honey Supplementation and Exercise: A Systematic Review

Honey is a natural substance formed primarily of carbohydrates (~80%) which also contains a number of other compounds purported to confer health benefits when consumed. Due to its carbohydrate composition (low glycaemic index, mostly fructose and glucose), honey may theoretically exert positive effects when consumed before, during or after exercise. This review therefore appraised research examining the effects of honey consumption in combination with exercise in humans. Online database (PubMed, MEDLINE, SPORTDiscus) searches were performed, yielding 273 results. Following duplicate removal and application of exclusion criteria, nine articles were reviewed. Large methodological differences existed in terms of exercise stimulus, population, and the nutritional interventions examined. All nine studies reported biochemical variables, with four examining the effects of honey on exercise performance, whilst five described perceptual responses. Acute supplementation around a single exercise session appeared to elicit similar performance, perceptual, and immunological responses compared with other carbohydrate sources, although some performance benefit has been observed relative to carbohydrate-free comparators. When consumed over a number of weeks, honey may dampen immunological perturbations arising from exercise and possibly improve markers of bone formation. More well-controlled research is required to better understand the role for honey in a food-first approach to exercise nutrition.

Carbohydrate Availability and Physical Performance: Physiological Overview and Practical Recommendations

Strong evidence during the last few decades has highlighted the importance of nutrition for sport performance, the role of carbohydrates (CHO) being of special interest. Glycogen is currently not only considered an energy substrate but also a regulator of the signaling pathways that regulate exercise-induced adaptations. Thus, low or high CHO availabilities can result in both beneficial or negative results depending on the purpose. On the one hand, the depletion of glycogen levels is a limiting factor of performance during sessions in which high exercise intensities are required; therefore ensuring a high CHO availability before and during exercise is of major importance. A high CHO availability has also been positively related to the exercise-induced adaptations to resistance training. By contrast, a low CHO availability seems to promote endurance-exercise-induced adaptations such as mitochondrial biogenesis and enhanced lipolysis. In the present narrative review, we aim to provide a holistic overview of how CHO availability impacts physical performance as well as to provide practical recommendations on how training and nutrition might be combined to maximize performance. Attending to the existing evidence, no universal recommendations regarding CHO intake can be given to athletes as nutrition should be periodized according to training loads and objectives.

Irritable bowel syndrome is underdiagnosed and ineffectively managed among endurance athletes

Lower gastrointestinal (GI) symptoms are common among endurance athletes and can impair performance. Symptom characteristics are similar to irritable bowel syndrome (IBS). No previous research has examined IBS diagnosis (medically or by diagnostic criteria) within this population. The objectives of this study were to determine the prevalence of IBS among endurance athletes and examine their GI symptom management strategies. A previously validated, online questionnaire assessed IBS diagnosis, the meeting of IBS diagnostic criteria (Rome III or Manning), general GI symptoms, and symptom mitigation strategies of endurance athletes. The questionnaire was distributed to United States athletes completing a marathon, ultra-marathon, half-distance triathlon, or full-distance triathlon. Medically diagnosed IBS was reported by 2.8% of endurance athletes. The total prevalence of IBS (n = 430) was 9.8% (medical diagnosis and Rome III). Athletes with IBS experienced more frequent symptoms during exercise as well as at rest; however, only 47.6% had consulted a medical professional. Over 56% of athletes experienced at least 1 symptom sometimes, often, or always during training and competition and 18.6% had symptoms that sometimes or often interrupted/prevented training. Almost half (45.8%) of athletes and 80.0% of athletes with IBS reported trying nutritional modifications to help ease symptoms while 20.6% and 52.4% used over-the-counter medications, respectively. Novelty Most endurance athletes who suffer from IBS are undiagnosed, while even more experience GI symptoms but do not fit diagnostic criteria. Despite using various symptom management methods, endurance athletes are still experiencing symptoms and could potentially benefit from current IBS-mitigating strategies.

Yogurt Drink Effectively Rehydrates Athletes After a Strenuous Exercise Session

Dehydration and electrolyte imbalance as a result of prolonged strenuous exercise leads to poor thermoregulation and impaired muscle performance. Thus, appropriate rehydration during and after exercise with a solution that has a balanced combination of nutrients including electrolytes, carbohydrates and proteins is crucial in preventing the side effects of dehydration. Yogurt drink as a traditional drink with an appropriate nutritious content could be used as an alternative to expensive commercially available drinks for rehydrating athletes after long exercises in warm and humid environments and in developing countries. In this cross-over trial we examined the rehydration potential of yogurt drink in comparison to water and a commercial drink after a strenuous exercise (cycling) session in a hot and humid environment. Blood measurements included blood osmolality, serum glucose, hematocrit and serum electrolytes. Urine measurements included urine volume, osmolality and electrolyte concentrations. The results showed that early after rehydration Yogurt drink compared to water significantly increased urine sodium (mmol/L) (138.8 ± 93.4 vs. 90.0 ± 50.7, P < 0.01), urine potassium (mmol/L) (105.6 ± 55.1 vs. 35.8 ± 22.0, P < 0.05) and urine chloride (mmol/L) (113.2 ± 28.4 vs. 35.8 ± 25.1 P < 0.01). This degree of improvement was the same as with the commercial drink for urine sodium, potassium, and chloride. Yogurt drink prevented dehydration-induced changes in the blood as it stabilized the hematocrit and serum sodium, potassium and osmolality within the normal range after exercise. Finally, our results indicated that yogurt drink, as a natural and affordable rehydration option, can be considered to restore fluid and electrolyte losses after strenuous exercises in hot and humid environments.

Liver and muscle glycogen oxidation and performance with dose variation of glucose-fructose ingestion during prolonged (3 h) exercise

PURPOSE

This study investigated the effect of small manipulations in carbohydrate (CHO) dose on exogenous and endogenous (liver and muscle) fuel selection during exercise.

METHOD

Eleven trained males cycled in a double-blind randomised order on 4 occasions at 60% [Formula: see text] for 3 h, followed by a 30-min time-trial whilst ingesting either 80 g h^-1 or 90 g h^-1 or 100 g h^{-1 13}C-glucose-¹³C-fructose [2:1] or placebo. CHO doses met, were marginally lower, or above previously reported intestinal saturation for glucose-fructose (90 g h^-1). Indirect calorimetry and stable mass isotope [¹³C] techniques were utilised to determine fuel use.

RESULT

Time-trial performance was 86.5 to 93%, 'likely, probable' improved with 90 g h^-1 compared 80 and 100 g h^-1. Exogenous CHO oxidation in the final hour was 9.8-10.0% higher with 100 g h^-1 compared with 80 and 90 g h^-1 (ES = 0.64-0.70, 95% CI 9.6, 1.4 to 17.7 and 8.2, 2.1 to 18.6). However, increasing CHO dose (100 g h^-1) increased muscle glycogen use (101.6 ± 16.6 g, ES = 0.60, 16.1, 0.9 to 31.4) and its relative contribution to energy expenditure (5.6 ± 8.4%, ES = 0.72, 5.6, 1.5 to 9.8 g) compared with 90 g h^-1. Absolute and relative muscle glycogen oxidation between 80 and 90 g h^-1 were similar (ES = 0.23 and 0.38) though a small absolute (85.4 ± 29.3 g, 6.2, - 23.5 to 11.1) and relative (34.9 ± 9.1 g, - 3.5, - 9.6 to 2.6) reduction was seen in 90 g h^-1 compared with 100 g h^-1. Liver glycogen oxidation was not significantly different between conditions (ES < 0.42). Total fat oxidation during the 3-h ride was similar in CHO conditions (ES < 0.28) but suppressed compared with placebo (ES = 1.05-1.51).

CONCLUSION

'Overdosing' intestinal transport for glucose-fructose appears to increase muscle glycogen reliance and negatively impact subsequent TT performance.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

Altitude Acclimatization Alleviates the Hypoxia-Induced Suppression of Exogenous Glucose Oxidation During Steady-State Aerobic Exercise

This study investigated how high-altitude (HA, 4300 m) acclimatization affected exogenous glucose oxidation during aerobic exercise. Sea-level (SL) residents (n = 14 men) performed 80-min, metabolically matched exercise (V˙O₂ ∼ 1.7 L/min) at SL and at HA < 5 h after arrival (acute HA, AHA) and following 22-d of HA acclimatization (chronic HA, CHA). During HA acclimatization, participants sustained a controlled negative energy balance (-40%) to simulate the “real world” conditions that lowlanders typically experience during HA sojourns. During exercise, participants consumed carbohydrate (CHO, n = 8, 65.25 g fructose + 79.75 g glucose, 1.8 g carbohydrate/min) or placebo (PLA, n = 6). Total carbohydrate oxidation was determined by indirect calorimetry and exogenous glucose oxidation by tracer technique with ¹³C. Participants lost (P ≤ 0.05, mean ± SD) 7.9 ± 1.9 kg body mass during the HA acclimatization and energy deficit period. In CHO, total exogenous glucose oxidized during the final 40 min of exercise was lower (P < 0.01) at AHA (7.4 ± 3.7 g) than SL (15.3 ± 2.2 g) and CHA (12.4 ± 2.3 g), but there were no differences between SL and CHA. Blood glucose and insulin increased (P ≤ 0.05) during the first 20 min of exercise in CHO, but not PLA. In CHO, glucose declined to pre-exercise concentrations as exercise continued at SL, but remained elevated (P ≤ 0.05) throughout exercise at AHA and CHA. Insulin increased during exercise in CHO, but the increase was greater (P ≤ 0.05) at AHA than at SL and CHA, which did not differ. Thus, while acute hypoxia suppressed exogenous glucose oxidation during steady-state aerobic exercise, that hypoxic suppression is alleviated following altitude acclimatization and concomitant negative energy balance.

Shorter Duration Time Trial Performance and Recovery Is Not Improved by Inclusion of Protein in a Multiple Carbohydrate Supplement

Wolfe, AS, Brandt, SA, Krause, IA, Mavison, RW, Aponte, JA, and Ferguson-Stegall, LM. Shorter duration time trial performance and recovery is not improved by inclusion of protein in a multiple carbohydrate supplement. J Strength Cond Res 31(9): 2509-2518, 2017-Ingesting multiple carbohydrate (CHO) types during exercise can improve endurance performance compared with single CHO only. Adding protein to a multiple CHO beverage has been shown to increase cycling time to exhaustion (TTE) compared with a single CHO beverage. However, it is unclear if improvements were due to multiple CHO or protein, and TTE protocols are not representative of typical race events. This study investigated whether adding protein to a multiple CHO beverage improved performance and recovery in 2 same-day cycling time trials (TTs) compared with isocaloric multiple CHO only. Ten cyclists (37.4 ± 8.9 years; V[Combining Dot Above]O2max 54.6 ± 6.5 ml·kg·min) performed a familiarization and 2 randomized, crossover, double-blinded experimental trials consisting of pretrial leg strength testing, 40-km TT, 30-min recovery, 10-km TT, and posttrial leg strength testing. Seven 275 ml doses of multiple CHO (MCO) or multiple CHO+protein (MCP) were ingested during the protocol. Blood glucose, lactate, heart rate (HR), and rating of perceived exertion (RPE) were also measured. Continuous variables were analyzed with paired t-tests, and repeated measures with repeated-measures analysis of variance. No differences existed between MCO and MCP in 40-km TT time (81.6 ± 2.8 vs. 81.9 ± 2.9 minutes, respectively, p = 0.94), or in 10-km time (24.0 ± 0.9 vs. 23.9 ± 1.0 minutes, p = 0.97). Blood glucose was higher before 10-km TT in MCO compared with MCP (3.78 ± 0.20 vs. 3.31 ± 0.19 mmol·L, p = 0.002). No treatment differences were found for lactate, HR, RPE, or strength recovery. When using a protocol and performance measures that replicate realistic, shorter duration events, adding protein to a multiple CHO beverage does not improve performance compared with multiple CHO only.

The Metabolic Flexibility of Hovering Vertebrate Nectarivores

Foraging hummingbirds and nectar bats oxidize both glucose and fructose from nectar at exceptionally high rates. Rapid sugar flux is made possible by adaptations to digestive, cardiovascular, and metabolic physiology affecting shared and distinct pathways for the processing of each sugar. Still, how these animals partition and regulate the metabolism of each sugar and whether this occurs differently between hummingbirds and bats remain unclear.

Quantifying the Effect of Carbohydrate Mouth Rinsing on Exercise Performance

The purpose of this study was to review the existing literature investigating carbohydrate mouth rinsing as an ergogenic aid using the effect sizes (ES) and percentage change in performance of the respective studies as outcome measures. A trivial-small average overall ES was present for the 25 studies included in the review (0.18, 95% confidence interval [CI] = 0.10-0.27). Effect sizes for the subgroups were ≥25 minutes (0.25, 95% CI = 0.14-0.36), ≤180 seconds (0.06, 95% CI = -0.03 to 0.15), resistance exercise (-0.09, 95% CI = -0.20 to 0.03) but the ES is still small. A subanalysis of ∼1-h cycling time trial performance resulted in an overall ES of 0.20 (95% CI = 0.02-0.38), and ES for performance time and power output of 0.31 (95% CI = -0.02 to 0.64) and 0.19 (95% CI = -0.09 to 0.46), respectively. Although ES were small, the average percentage change in performance in ∼1-hour trials was 2.48%, which may have implications for elite performers as this is greater than the 1.30% smallest worthwhile change recommended in the past research.

International society of sports nutrition position stand: nutrient timing

The International Society of Sports Nutrition (ISSN) provides an objective and critical review regarding the timing of macronutrients in reference to healthy, exercising adults and in particular highly trained individuals on exercise performance and body composition. The following points summarize the position of the ISSN:

Nutrient timing incorporates the use of methodical planning and eating of whole foods, fortified foods and dietary supplements. The timing of energy intake and the ratio of certain ingested macronutrients may enhance recovery and tissue repair, augment muscle protein synthesis (MPS), and improve mood states following high-volume or intense exercise.

Endogenous glycogen stores are maximized by following a high-carbohydrate diet (8–12 g of carbohydrate/kg/day [g/kg/day]); moreover, these stores are depleted most by high volume exercise.

If rapid restoration of glycogen is required (< 4 h of recovery time) then the following strategies should be considered:

aggressive carbohydrate refeeding (1.2 g/kg/h) with a preference towards carbohydrate sources that have a high (> 70) glycemic index

the addition of caffeine (3–8 mg/kg)

combining carbohydrates (0.8 g/kg/h) with protein (0.2–0.4 g/kg/h)

Extended (> 60 min) bouts of high intensity (> 70% VO₂max) exercise challenge fuel supply and fluid regulation, thus carbohydrate should be consumed at a rate of ~30–60 g of carbohydrate/h in a 6–8% carbohydrate-electrolyte solution (6–12 fluid ounces) every 10–15 min throughout the entire exercise bout, particularly in those exercise bouts that span beyond 70 min. When carbohydrate delivery is inadequate, adding protein may help increase performance, ameliorate muscle damage, promote euglycemia and facilitate glycogen re-synthesis.

Carbohydrate ingestion throughout resistance exercise (e.g., 3–6 sets of 8–12 repetition maximum [RM] using multiple exercises targeting all major muscle groups) has been shown to promote euglycemia and higher glycogen stores. Consuming carbohydrate solely or in combination with protein during resistance exercise increases muscle glycogen stores, ameliorates muscle damage, and facilitates greater acute and chronic training adaptations.

Meeting the total daily intake of protein, preferably with evenly spaced protein feedings (approximately every 3 h during the day), should be viewed as a primary area of emphasis for exercising individuals.

Ingestion of essential amino acids (EAA; approximately 10 g)either in free form or as part of a protein bolus of approximately 20–40 g has been shown to maximally stimulate muscle protein synthesis (MPS).

Pre- and/or post-exercise nutritional interventions (carbohydrate + protein or protein alone) may operate as an effective strategy to support increases in strength and improvements in body composition. However, the size and timing of a pre-exercise meal may impact the extent to which post-exercise protein feeding is required.

Post-exercise ingestion (immediately to 2-h post) of high-quality protein sources stimulates robust increases in MPS.

In non-exercising scenarios, changing the frequency of meals has shown limited impact on weight loss and body composition, with stronger evidence to indicate meal frequency can favorably improve appetite and satiety. More research is needed to determine the influence of combining an exercise program with altered meal frequencies on weight loss and body composition with preliminary research indicating a potential benefit.

Ingesting a 20–40 g protein dose (0.25–0.40 g/kg body mass/dose) of a high-quality source every three to 4 h appears to most favorably affect MPS rates when compared to other dietary patterns and is associated with improved body composition and performance outcomes.

Consuming casein protein (~ 30–40 g) prior to sleep can acutely increase MPS and metabolic rate throughout the night without influencing lipolysis.

Does Carbohydrate Intake During Endurance Running Improve Performance? A Critical Review

Wilson, PB. Does carbohydrate intake during endurance running improve performance? A critical review. J Strength Cond Res 30(12): 3539-3559, 2016-Previous review articles assessing the effects of carbohydrate ingestion during prolonged exercise have not focused on running. Given the popularity of distance running and the widespread use of carbohydrate supplements, this article reviewed the evidence for carbohydrate ingestion during endurance running. The criteria for inclusion were (a) experimental studies reported in English language including a performance task, (b) moderate-to-high intensity exercise >60 minutes (intermittent excluded), and (c) carbohydrate ingestion (mouth rinsing excluded). Thirty studies were identified with 76 women and 505 men. Thirteen of the 17 studies comparing a carbohydrate beverage(s) with water or a placebo found a between-condition performance benefit with carbohydrate, although heterogeneity in protocols precludes clear generalizations about the expected effect sizes. Additional evidence suggests that (a) performance benefits are most likely to occur during events >2 hours, although several studies showed benefits for tasks lasting 90-120 minutes; (b) consuming carbohydrate beverages above ad libitum levels increases gastrointestinal discomfort without improving performance; (c) carbohydrate gels do not influence performance for events lasting 16-21 km; and (d) multiple saccharides may benefit events >2 hours if intake is ≥1.3 g·min Given that most participants were fasted young men, inferences regarding women, adolescents, older runners, and those competing in fed conditions are hampered. Future studies should address these limitations to further elucidate the role of carbohydrate ingestion during endurance running.

A systematic review and meta-analysis of carbohydrate benefits associated with randomized controlled competition-based performance trials

Background

Carbohydrate supplements are widely used by athletes as an ergogenic aid before and during sports events. The present systematic review and meta-analysis aimed at synthesizing all available data from randomized controlled trials performed under real-life conditions.

Methods

MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched systematically up to February 2015. Study groups were categorized according to test mode and type of performance measurement. Subgroup analyses were done with reference to exercise duration and range of carbohydrate concentration. Random effects and fixed effect meta-analyses were performed using the Software package by the Cochrane Collaboration Review Manager 5.3.

Results

Twenty-four randomized controlled trials met the objectives and were included in the present systematic review, 16 of which provided data for meta-analyses. Carbohydrate supplementations were associated with a significantly shorter exercise time in groups performing submaximal exercise followed by a time trial [mean difference −0.9 min (95 % confidence interval −1.7, −0.2), p = 0.02] as compared to controls. Subgroup analysis showed that improvements were specific for studies administering a concentration of carbohydrates between 6 and 8 % [mean difference −1.0 min (95 % confidence interval −1.9, −0.0), p = 0.04]. Concerning groups with submaximal exercise followed by a time trial measuring power accomplished within a fixed time or distance, mean power output was significantly higher following carbohydrate load (mean difference 20.2 W (95 % confidence interval 9.0, 31.5), p = 0.0004]. Likewise, mean power output was significantly increased following carbohydrate intervention in groups with time trial measuring power within a fixed time or distance (mean difference 8.1 W (95 % confidence interval 0.5, 15.7) p = 0.04].

Conclusion

Due to the limitations of this systematic review, results can only be applied to a subset of athletes (trained male cyclists). For those, we could observe a potential ergogenic benefit of carbohydrate supplementation especially in a concentration range between 6 and 8 % when exercising longer than 90 min.

Electronic supplementary material

The online version of this article (doi:10.1186/s12970-016-0139-6) contains supplementary material, which is available to authorized users.

Mouth Rinsing With Carbohydrate Solutions at the Postprandial State Fail to Improve Performance During Simulated Cycling Time Trials

Mouth rinsing with carbohydrate (CHO) solutions during cycling time trials results in performance enhancements; however, most studies have used approximately 6% CHO solutions. Therefore, the purpose of this study was to compare the effectiveness of mouth rinsing with 4, 6, and 8% CHO solutions on 1-hour simulated cycling time trial performance. On 4 occasions, 7 trained male cyclists completed at the postprandial period, a set amount of work as fast as possible in a randomized counterbalanced order. The subjects rinsed their mouth for 5 seconds, on completion of each 12.5% of the trial, with 25 ml of a non-CHO placebo and 4, 6, and 8% CHO solutions. No additional fluids were consumed during the time trial. Heart rate (HR), ratings of perceived exertion (RPE), thirst (TH), and subjective feelings (SF) were recorded after each rinse. Furthermore, blood samples were drawn every 25% of the trial to measure blood glucose and blood lactate concentrations, whereas whole-body CHO oxidation was monitored continuously. Time to completion was not significant between conditions with the placebo, 4, 6, and 8% conditions completing the trials in 62.0 ± 3.0, 62.8 ± 4.0, 63.4 ± 3.4, and 63 ± 4.0 minutes, respectively. There were no significant differences between conditions in any of the variables mentioned above; however, significant time effects were observed for HR, RPE, TH, and SF. Post hoc analysis showed that TH and SF of subjects in the CHO conditions but not in the placebo were significantly increased by completion of the time trial. In conclusion, mouth rinsing with CHO solutions did not impact 1-hour cycling performance in the postprandial period and in the absence of fluid intake. Our findings suggest that there is scope for further research to explore the activation regions of the brain and whether they are receptive to CHO dose, before specific recommendations for athletic populations are established. Consequently, mouth rinsing as a practical strategy for coaches and athletes is questionable under specific conditions and should be carefully considered before its inclusion. Emphasis should be focused on appropriate dietary and fluid strategies during training and competition.

Effect of carbohydrate feeding on the bone metabolic response to running

Bone resorption is increased after running, with no change in bone formation. Feeding during exercise might attenuate this increase, preventing associated problems for bone. This study investigated the immediate and short-term bone metabolic responses to carbohydrate (CHO) feeding during treadmill running. Ten men completed two 7-day trials, once being fed CHO (8% glucose immediately before, every 20 min during, and immediately after exercise at a rate of 0.7 g CHO·kg body mass⁻¹·h⁻¹) and once being fed placebo (PBO). On day 4 of each trial, participants completed a 120-min treadmill run at 70% of maximal oxygen consumption (V̇o_{2 max}). Blood was taken at baseline (BASE), immediately after exercise (EE), after 60 (R1) and 120 (R2) min of recovery, and on three follow-up days (FU1-FU3). Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH₂-terminal propeptides of procollagen type 1 (P1NP)] were measured, along with osteocalcin (OC), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate, glucagon-like peptide-2 (GLP-2), interleukin-6 (IL-6), insulin, cortisol, leptin, and osteoprotogerin (OPG). Area under the curve was calculated in terms of the immediate (BASE, EE, R1, and R2) and short-term (BASE, FU1, FU2, and FU3) responses to exercise. β-CTX, P1NP, and IL-6 responses to exercise were significantly lower in the immediate postexercise period with CHO feeding compared with PBO (β-CTX: P = 0.028; P1NP: P = 0.021; IL-6: P = 0.036), although there was no difference in the short-term response (β-CTX: P = 0.856; P1NP: P = 0.721; IL-6: P = 0.327). No other variable was significantly affected by CHO feeding during exercise. We conclude that CHO feeding during exercise attenuated the β-CTX and P1NP responses in the hours but not days following exercise, indicating an acute effect of CHO feeding on bone turnover.

O uso do carboidrato antes da atividade física como recurso ergogênico: revisão sistemática

A dieta dos atletas requer aporte energético adequado, sendo a principal fonte energética os carboidratos CHO que são encontrados livremente na corrente sanguínea ou armazenados nos músculos e no fígado. Com base na rotina de treinos e competições, ou mesmo na quantidade exacerbada de energia necessária, é comum a necessidade de suplementação de CHO, seja na forma de bebidas, géis, barras ou balas energéticas, antes, durante ou depois da atividade física. Devido à importância dos CHO foram reunidos estudos que testaram a suplementação com diferentes CHO antes do exercício para aumento da performance. Foram investigados artigos e teses cuja publicação ocorreu a partir de 2006 em bases científicas eletrônicas e banco de teses de faculdades renomadas na área. Os CHO podem ser divididos segundo a quantidade de moléculas que o compõem, as quais também são diferenciadas também por digestão, absorção, viscosidade, dulçor, índice glicêmico IG e oxidação durante a atividade. Comparando-se a taxa de oxidação, foram encontrados melhores resultados quando os CHO ingeridos são de alto teor de IG glicose e sacarose e baixo teor de IG frutose ao se realizar atividade de média a alta intensidade de longa duração. A ingestão de CHO antes do exercício mostrou-se eficiente nos nove estudos analisados, sendo que dois deles apresentaram relevância p < 0,005. Mesmo com a ingestão de CHO com diferentes IG, observou-se melhora, não sendo relatada hipoglicemia de rebote como teorizado na literatura. A suplementação de CHO com a composição e administração apropriadas mostrou-se eficiente para aumento do desempenho físico.

Carbon stable-isotope tracking in breath for comparative studies of fuel use

Almost half a century ago, researchers demonstrated that the ratio of stable carbon isotopes in exhaled breath of rats and humans could reveal the oxidation of labeled substrates in vivo, opening a new chapter in the study of fuel use, the fate of ingested substrates, and aerobic metabolism. Until recently, the combined use of respirometry and stable-isotope tracer techniques had not been broadly employed to study fuel use in other animal groups. In this review, we summarize the history of this approach in human and animal research and define best practices that maximize its utility. We also summarize several case studies that use stable-isotope measurements of breath to explore the limits of aerobic metabolism and substrate turnover among several species and various physiological states. We highlight the importance of a comparative approach in revealing the profound effects that phylogeny, ecology, and behavior can have in shaping aerobic metabolism and energetics as well as the fundamental biological principles that underlie fuel use and metabolic function across taxa. New analytical equipment and refinement of methodology make the combined use of respirometry and stable-isotope tracer techniques simpler to perform, less costly, and more field ready than ever before.

A step towards personalized sports nutrition: carbohydrate intake during exercise

There have been significant changes in the understanding of the role of carbohydrates during endurance exercise in recent years, which allows for more specific and more personalized advice with regard to carbohydrate ingestion during exercise. The new proposed guidelines take into account the duration (and intensity) of exercise and advice is not restricted to the amount of carbohydrate; it also gives direction with respect to the type of carbohydrate. Studies have shown that during exercise lasting approximately 1 h in duration, a mouth rinse or small amounts of carbohydrate can result in a performance benefit. A single carbohydrate source can be oxidized at rates up to approximately 60 g/h and this is the recommendation for exercise that is more prolonged (2-3 h). For ultra-endurance events, the recommendation is higher at approximately 90 g/h. Carbohydrate ingested at such high ingestion rates must be a multiple transportable carbohydrates to allow high oxidation rates and prevent the accumulation of carbohydrate in the intestine. The source of the carbohydrate may be a liquid, semisolid, or solid, and the recommendations may need to be adjusted downward when the absolute exercise intensity is low and thus carbohydrate oxidation rates are also low. Carbohydrate intake advice is independent of body weight as well as training status. Therefore, although these guidelines apply to most athletes, they are highly dependent on the type and duration of activity. These new guidelines may replace the generic existing guidelines for carbohydrate intake during endurance exercise.

Optimal composition of fluid-replacement beverages

The objective of this article is to provide a review of the fundamental aspects of body fluid balance and the physiological consequences of water imbalances, as well as discuss considerations for the optimal composition of a fluid replacement beverage across a broad range of applications. Early pioneering research involving fluid replacement in persons suffering from diarrheal disease and in military, occupational, and athlete populations incurring exercise- and/or heat-induced sweat losses has provided much of the insight regarding basic principles on beverage palatability, voluntary fluid intake, fluid absorption, and fluid retention. We review this work and also discuss more recent advances in the understanding of fluid replacement as it applies to various populations (military, athletes, occupational, men, women, children, and older adults) and situations (pathophysiological factors, spaceflight, bed rest, long plane flights, heat stress, altitude/cold exposure, and recreational exercise). We discuss how beverage carbohydrate and electrolytes impact fluid replacement. We also discuss nutrients and compounds that are often included in fluid-replacement beverages to augment physiological functions unrelated to hydration, such as the provision of energy. The optimal composition of a fluid-replacement beverage depends upon the source of the fluid loss, whether from sweat, urine, respiration, or diarrhea/vomiting. It is also apparent that the optimal fluid-replacement beverage is one that is customized according to specific physiological needs, environmental conditions, desired benefits, and individual characteristics and taste preferences.

Acute nutritional ketosis: implications for exercise performance and metabolism

Ketone bodies acetoacetate (AcAc) and D-β-hydroxybutyrate (βHB) may provide an alternative carbon source to fuel exercise when delivered acutely in nutritional form. The metabolic actions of ketone bodies are based on sound evolutionary principles to prolong survival during caloric deprivation. By harnessing the potential of these metabolic actions during exercise, athletic performance could be influenced, providing a useful model for the application of ketosis in therapeutic conditions. This article examines the energetic implications of ketone body utilisation with particular reference to exercise metabolism and substrate energetics.

Perturbed energy balance and hydration status in ultra-endurance runners during a 24 h ultra-marathon

The present study aimed to assess the adequacy of energy, macronutrients and water intakes of ultra-endurance runners (UER) competing in a 24 h ultra-marathon (distance range: 122-208 km). The ad libitum food and fluid intakes of the UER (n 25) were recorded throughout the competition and analysed using dietary analysis software. Body mass (BM), urinary ketone presence, plasma osmolality (POsmol) and volume change were determined at pre- and post-competition time points. Data were analysed using appropriate t tests, with significance set at P <0·05. The total energy intake and expenditure of the UER were 20 (sd 12) and 55 (sd 11) MJ, respectively (control (CON) (n 17): 12 (sd 1) and 14 (sd 5) MJ, respectively). The protein, carbohydrate and fat intakes of the UER were 1·1 (sd 0·4), 11·3 (sd 7·0) and 1·5 (sd 0·7) g/kg BM, respectively. The rate of carbohydrate intake during the competition was 37 (sd 24) g/h. The total water intake of the UER was 9·1 (sd 4·0) litres (CON: 2·1 (sd 1·0) litres), while the rate of water intake was 378 (sd 164) ml/h. Significant BM loss occurred at pre- to post-competition time points (P =0·001) in the UER (1·6 (sd 2·0) %). No significant changes in POsmol values were observed at pre- (285 (sd 11) mOsmol/kg) to post-competition (287 (sd 10) mOsmol/kg) time points in the UER and were lower than those recorded in the CON group (P <0·05). However, plasma volume (PV) increased at post-competition time points in the UER (10·2 (sd 9·7) %; P <0·001). Urinary ketones were evident in the post-competition samples of 90 % of the UER. Energy deficit was observed in all the UER, with only one UER achieving the benchmark recommendations for carbohydrate intake during endurance exercise. Despite the relatively low water intake rates recorded in the UER, hypohydration does not appear to be an issue, considering increases in PV values observed in the majority (80 %) of the UER. Population-specific dietary recommendations may be beneficial and warranted.

Effects of a carbohydrate and caffeine gel on intermittent sprint performance in recreationally trained males

We investigated the effects of ingesting carbohydrate gels with and without caffeine on a ~90-minute, four blocks intermittent sprint test (IST), in 12 recreationally trained male athletes. Using a cross-over design, one 70 ml dose of gel containing either 25 g of carbohydrate with (CHOCAF) or without (CHO) 100 mg of caffeine, or a non-caloric placebo (PL) was ingested on three occasions: one hour before, immediately prior to and during the IST. Blood glucose, rating of perceived exertion (RPE) and fatigue index (FI) were analysed. Glucose showed significantly higher values for both CHOCAF and CHO at the first (p=0.005 and p=0.000, respectively), second (p=0.009 and 0.008, respectively) and third (p=0.003 and 0.001, respectively) blocks when compared with PL, while only CHOCAF was significantly different to PL (p=0.002) at the fourth block. CHOCAF showed an improved FI (mean 5.0, s =1.7) compared with CHO (mean 7.6, s =2.6; p=0.006) and PL (mean 7.4, s =2.4; p=0.005), a significantly lower RPE (mean 14.2, s =2) compared with PL (mean 15.3, s =2; p=0.003) and a trend in respect of CHO (mean 14.9, s =2.3; p=0.056) after the third block. In conclusion, ingesting CHOCAF one hour before, prior to and during an IST is effective at transiently reducing fatigue and RPE whilst maintaining higher glucose levels at the final stages of the exercise.

The effect of carbohydrate and marine peptide hydrolysate co-ingestion on endurance exercise metabolism and performance

BACKGROUND

The purpose of this study was to examine the efficacy of introducing a fish protein hydrolysate (PEP) concurrently with carbohydrate (CHO) and whey protein (PRO) on endurance exercise metabolism and performance.

METHODS

In a randomised, double blind crossover design, 12 male volunteers completed an initial familiarisation followed by three experimental trials. The trials consisted of a 90 min cycle task corresponding to 50% of predetermined maximum power output, followed by a 5 km time trial (TT). At 15 min intervals during the 90 min cycle task, participants consumed 180 ml of CHO (67 g(.)hr(-1) of maltodextrin), CHO-PRO (53.1 g(.)hr of CHO, 13.6 g(.)hr(-1) of whey protein) or CHO-PRO-PEP (53.1 g(.)hr(-1) of CHO, 11 g(.)hr(-1) of whey protein and 2.4 g(.)hr(-1)of hydrolyzed marine peptides).

RESULTS AND CONCLUSIONS

During the 90 min cycle task, the respiratory exchange ratio (RER) in the CHO-PRO condition was significantly higher than CHO (p < 0.001) and CHO-PRO-PEP (p < 0.001). Additionally, mean heart rate for the CHO condition was significantly lower than that for CHO-PRO (p = 0.021). Time-to-complete the 5 km TT was not significantly different between conditions (m ± SD: 456 ± 16, 456 ± 18 and 455 ± 21 sec for CHO, CHO-PRO and CHO-PRO-PEP respectively, p = 0.98). Although the addition of hydrolyzed marine peptides appeared to influence metabolism during endurance exercise in the current study, it did not provide an ergogenic benefit as assessed by 5 km TT performance.

The ingestion of combined carbohydrates does not alter metabolic responses or performance capacity during soccer-specific exercise in the heat compared to ingestion of a single carbohydrate

This study was designed to investigate the effect of ingesting a glucose plus fructose solution on the metabolic responses to soccer-specific exercise in the heat and the impact on subsequent exercise capacity. Eleven male soccer players performed a 90 min soccer-specific protocol on three occasions. Either 3 ml · kg(-1) body mass of a solution containing glucose (1 g · min(-1) glucose) (GLU), or glucose (0.66 g · min(-1)) plus fructose (0.33 g · min(-1)) (MIX) or placebo (PLA) was consumed every 15 minutes. Respiratory measures were undertaken at 15-min intervals, blood samples were drawn at rest, half-time and on completion of the protocol, and muscle glycogen concentration was assessed pre- and post-exercise. Following the soccer-specific protocol the Cunningham and Faulkner test was performed. No significant differences in post-exercise muscle glycogen concentration (PLA, 62.99 ± 8.39 mmol · kg wet weight(-1); GLU 68.62 ± 2.70; mmol · kg wet weight(-1) and MIX 76.63 ± 6.92 mmol · kg wet weight(-1)) or exercise capacity (PLA, 73.62 ± 8.61 s; GLU, 77.11 ± 7.17 s; MIX, 83.04 ± 9.65 s) were observed between treatments (P > 0.05). However, total carbohydrate oxidation was significantly increased during MIX compared with PLA (P < 0.05). These results suggest that when ingested in moderate amounts, the type of carbohydrate does not influence metabolism during soccer-specific intermittent exercise or affect performance capacity after exercise in the heat.

Carbohydrate and exercise performance: the role of multiple transportable carbohydrates

PURPOSE OF REVIEW

Carbohydrate feeding has been shown to be ergogenic, but recently substantial advances have been made in optimizing the guidelines for carbohydrate intake during prolonged exercise.

RECENT FINDINGS

It was found that limitations to carbohydrate oxidation were in the absorptive process most likely because of a saturation of carbohydrate transporters. By using a combination of carbohydrates that use different intestinal transporters for absorption it was shown that carbohydrate delivery and oxidation could be increased. Studies demonstrated increases in exogenous carbohydrate oxidation rates of up to 65% of glucose: fructose compared with glucose only. Exogenous carbohydrate oxidation rates reach values of 1.75 g/min whereas previously it was thought that 1 g/min was the absolute maximum. The increased carbohydrate oxidation with multiple transportable carbohydrates was accompanied by increased fluid delivery and improved oxidation efficiency, and thus the likelihood of gastrointestinal distress may be diminished. Studies also demonstrated reduced fatigue and improved exercise performance with multiple transportable carbohydrates compared with a single carbohydrate.

SUMMARY

Multiple transportable carbohydrates, ingested at high rates, can be beneficial during endurance sports in which the duration of exercise is 3 h or more.

Fuel selection and cycling endurance performance with ingestion of [13C]glucose: evidence for a carbohydrate dose response

Endurance performance and fuel selection while ingesting glucose (15, 30, and 60 g/h) was studied in 12 cyclists during a 2-h constant-load ride [∼77% peak O2 uptake] followed by a 20-km time trial. Total fat and carbohydrate (CHO) oxidation and oxidation of exogenous glucose, plasma glucose, glucose released from the liver, and muscle glycogen were computed using indirect respiratory calorimetry and tracer techniques. Relative to placebo (210 ± 36 W), glucose ingestion increased the time trial mean power output (%improvement, 90% confidence limits: 7.4, 1.4 to 13.4 for 15 g/h; 8.3, 1.4 to 15.2 for 30 g/h; and 10.7, 1.8 to 19.6 for 60 g/h glucose ingested; effect size = 0.46). With 60 g/h glucose, mean power was 2.3, 0.4 to 4.2% higher, and 3.1, 0.5 to 5.7% higher than with 30 and 15 g/h, respectively, suggesting a relationship between the dose of glucose ingested and improvements in endurance performance. Exogenous glucose oxidation increased with ingestion rate (0.17 ± 0.04, 0.33 ± 0.04, and 0.52 ± 0.09 g/min for 15, 30, and 60 g/h glucose), but endogenous CHO oxidation was reduced only with 30 and 60 g/h due to the progressive inhibition of glucose released from the liver (probably related to higher plasma insulin concentration) with increasing ingestion rate without evidence for muscle glycogen sparing. Thus ingestion of glucose at low rates improved cycling time trial performance in a dose-dependent manner. This was associated with a small increase in CHO oxidation without any reduction in muscle glycogen utilization.