Fructose-maltodextrin ratio in a carbohydrate-electrolyte solution differentially affects exogenous carbohydrate oxidation rate, gut comfort, and performance

What is a cycling race simulation anyway: a review on protocols to assess durability in cycling

Physiological resilience or durability is now recognised as a determinant of endurance performance such as road cycling. Reliable, ecologically valid and standardised performance tests in laboratory-based cycling protocols have to be established to investigate mechanisms underpinning, and interventions improving durability. This review aims to provide an overview of available race simulation protocols in the literature and examines its rigour around themes that influence durability including (i) exercise intensity anchoring and (ii) carbohydrate intake whilst also (iii) inspecting reliability and justification of the developed protocols. Using a systematic search approach, 48 articles were identified that met our criteria as a cycling race simulation. Most protocols presented limitations to be recommended as exercise test to investigate durability, such as not appropriately addressing the influence of exercise intensity domains by anchoring exercise intensity as % peak power or % V ˙ O2max. Ten articles provided reliability data, but only one articles under the appropriate conditions. Most studies sufficiently controlled nutrition during trials but not in the days leading to the trials or just before the trials. Thus, there is a paucity in protocols that combine justification and reliability with optimal nutritional support and mimic the true demands of a road-cycling race. This review lists an overview of protocols that researchers could use with caution to select a protocol for future experiments, but encourages further development of improved protocols, including utilisation of virtual software applications.

Self-reported carbohydrate supercompensation and supplementation strategies adopted by Olympic triathlon athletes

The aim of the present study was to describe the use of tapering, carbohydrate (CHO) supercompensation, and supplementation strategies self-reported by athletes in the Olympic triathlon category. A total of 72 triathletes (61 males and 11 females) answered an online questionnaire about their training and performance, supercompensation strategies, carbohydrate supplementation, and use of supplements and other ergogenic substances. The information was summarized and subjected to descriptive analysis. Shapiro-Wilk test was applied to check data normality. The t-test was used to investigate differences in the analyzed variables between sexes. Almost all triathletes reported to have performed tapering (93.05%) and approximately half of them adopted a CHO supercompensation strategy (48.61%); updated CHO supercompensation was the most used strategy (27.77%). Most participants (86.11%) used CHO supplementation during competitions, but in amounts below the 60 g/h recommended for most athletes (96.77%). Thus, since few triathletes performed supercompensation, in addition to the insufficient amount of supplemented carbohydrate taken by them, it could be concluded that triathletes were not sufficiently aware of nutritional recommendations or did not adopt them.

Functional Beverages in the 21st Century

Underlying the dawn of humanity was primarily the search for food and access to drinking water. Over the course of civilization, there has been a significant increase in drinking water quality. By the average of the nutritional standards, the daily water demand is 2.5 L (also including liquid products such as tea, coffee, or soup). However, it is worth noticing that the need is strictly individual for each person and depends on two major factors, namely, epidemiological (sex, age state of health, lifestyle, and diet) and environmental (humidity and air temperature). Currently, our diet is more and more often enriched with isotonic drinks, functional drinks, or drinks bearing the hallmarks of health-promoting products. As a result, manufacturing companies compete to present more interesting beverages with complex compositions. This article will discuss both the composition of functional beverages and their impact on health.

Carbohydrate intake before and during high intensity exercise with reduced muscle glycogen availability affects the speed of muscle reoxygenation and performance

Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr^-1) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS [Formula: see text], HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s^-1) existed in PLA after the 1st (Δ - 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ - 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.

Visceral sensitivity correlates with gastrointestinal symptoms in runners during training but does not negatively impact peri-exercise fueling

OBJECTIVES

This study aimed to evaluate the associations between several psychological factors (stress, anxiety, body vigilance, and visceral sensitivity) and gastrointestinal (GI) symptoms in runners, as well as whether any of these factors impact pre-exercise and during-exercise fueling.

METHODS

A virtual/online observational survey-based study with 82 (43 male and 39 female) runners was conducted. The Perceived Stress Scale (PSS)-14, State-Trait Inventory for Cognitive and Somatic Anxiety (STICSA-Trait), Body Vigilance Scale (BVS), and Visceral Sensitivity Index (VSI) were assessed. GI symptoms during runs over 1 week, as well as nutrient intakes from food and fluid consumed 4 h before and during runs, were recorded. GI problems were quantified as the percentage of runs that a participant reported at least one symptom  ≥ 3 out of 10.

RESULTS

VSI scores significantly correlated with the occurrence of all, upper, and lower GI symptoms during runs (ρ  =  0.32-0.38; p < 0.003), and these associations remained significant in partial correlation analyses. No significant associations were observed between GI symptom occurrence and scores on the BVS, PSS-14, or STICSA-Trait. In a subset of 72 runners with available nutrition data, intakes of energy, macronutrients, fluid, and caffeine before and during runs did not seem to be lower in those who had higher PSS-14, STICSA-Trait, BVS, or VSI scores, which was contrary to what was hypothesized.

CONCLUSIONS

Runners' visceral sensitivity levels associate with GI symptoms during training over a week, but the impact of this and other psychological factors on nutritional intake is uncertain, particularly around competition.

Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h-1 versus 90 g h-1 at different ratios

Purpose

This study aimed to investigate whether carbohydrate ingestion during 3 h long endurance exercise in highly trained cyclists at a rate of 120 g h⁻¹ in 0.8:1 ratio between fructose and glucose-based carbohydrates would result in higher exogenous and lower endogenous carbohydrate oxidation rates as compared to ingestion of 90 g h⁻¹ in 1:2 ratio, which is the currently recommended approach for exercise of this duration.

Methods

Eleven male participants (V̇O_2peak 62.6 ± 7 mL kg⁻¹ min⁻¹, gas exchange threshold (GET) 270 ± 17 W and Respiratory compensation point 328 ± 32 W) completed the study involving 4 experimental visits consisting of 3 h cycling commencing after an overnight fast at an intensity equivalent to 95% GET. During the trials they received carbohydrates at an average rate of 120 or 90 g h⁻¹ in 0.8:1 or 1:2 fructose-maltodextrin ratio, respectively. Carbohydrates were naturally high or low in ¹³C stable isotopes enabling subsequent calculations of exogenous and endogenous carbohydrate oxidation rates.

Results

Exogenous carbohydrate oxidation rates were higher in the 120 g h⁻¹ condition (120–180 min: 1.51 ± 0.22 g min⁻¹) as compared to the 90 g h⁻¹ condition (1.29 ± 0.16 g min⁻¹; p = 0.026). Endogenous carbohydrate oxidation rates did not differ between conditions (2.15 ± 0.30 and 2.20 ± 0.33 g min⁻¹ for 120 and 90 g h⁻¹ conditions, respectively; p = 0.786).

Conclusions

The results suggest that carbohydrate ingestion at 120 g h⁻¹ in 0.8:1 fructose-maltodextrin ratio as compared with 90 g h⁻¹ in 1:2 ratio offers higher exogenous carbohydrate oxidation rates but no additional sparing of endogenous carbohydrates. Further studies should investigate potential performance effects of such carbohydrate ingestion strategies.

13C-glucose-fructose labeling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew, or coingestion

We examined the effects of carbohydrate (CHO) delivery form on exogenous CHO oxidation, gastrointestinal discomfort, and exercise capacity. In a randomized repeated-measures design [after 24 h of high CHO intake (8 g·kg^-1) and preexercise meal (2 g·kg^-1)], nine trained males ingested 120 g CHO·h^-1 from fluid (DRINK), semisolid gel (GEL), solid jelly chew (CHEW), or a coingestion approach (MIX). Participants cycled for 180 min at 95% lactate threshold, followed by an exercise capacity test (150% lactate threshold). Peak rates of exogenous CHO oxidation (DRINK 1.56 ± 0.16, GEL 1.58 ± 0.13, CHEW 1.59 ± 0.08, MIX 1.66 ± 0.02 g·min^-1) and oxidation efficiency (DRINK 72 ± 8%, GEL 72 ± 5%, CHEW 75 ± 5%, MIX, 75 ± 6%) were not different between trials (all P > 0.05). Despite ingesting 120 g·h^-1, participants reported minimal symptoms of gastrointestinal distress across all trials. Exercise capacity was also not significantly different (all P > 0.05) between conditions (DRINK 446 ± 350, GEL 529 ± 396, CHEW 596 ± 416, MIX 469 ± 395 s). Data represent the first time that rates of exogenous CHO oxidation (via stable isotope methodology) have been simultaneously assessed with feeding strategies (i.e., preexercise CHO feeding and the different forms and combinations of CHO during exercise) commonly adopted by elite endurance athletes. We conclude that 120 g·h^-1 CHO (in a 1:0.8 ratio of maltodextrin or glucose to fructose) is a practically tolerable strategy to promote high CHO availability and oxidation during exercise.NEW & NOTEWORTHY We demonstrate comparable rates of exogenous CHO oxidation from fluid, semisolid, solid, or a combination of sources. Considering the sustained high rates of total and exogenous CHO oxidation and relative lack of gastrointestinal symptoms, consuming 120 g CHO·h^-1 appears to be a well-tolerated strategy to promote high CHO availability during exercise. Additionally, this is the first time that rates of exogenous CHO oxidation have been assessed with feeding strategies (e.g., coingestion of multiple CHO forms) typically reported by endurance athletes.

New Horizons in Carbohydrate Research and Application for Endurance Athletes

The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.

The Hydrating Effects of Hypertonic, Isotonic and Hypotonic Sports Drinks and Waters on Central Hydration During Continuous Exercise: A Systematic Meta-Analysis and Perspective

Background

Body-fluid loss during prolonged continuous exercise can impair cardiovascular function, harming performance. Delta percent plasma volume (dPV) represents the change in central and circulatory body-water volume and therefore hydration during exercise; however, the effect of carbohydrate–electrolyte drinks and water on the dPV response is unclear.

Objective

To determine by meta-analysis the effects of ingested hypertonic (> 300 mOsmol kg⁻¹), isotonic (275–300 mOsmol kg⁻¹) and hypotonic (< 275 mOsmol kg⁻¹) drinks containing carbohydrate and electrolyte ([Na⁺] < 50 mmol L⁻¹), and non-carbohydrate drinks/water (< 40 mOsmol kg⁻¹) on dPV during continuous exercise.

Methods

A systematic review produced 28 qualifying studies and 68 drink treatment effects. Random-effects meta-analyses with repeated measures provided estimates of effects and probability of superiority (p₊) during 0–180 min of exercise, adjusted for drink osmolality, ingestion rate, metabolic rate and a weakly informative Bayesian prior.

Results

Mean drink effects on dPV were: hypertonic − 7.4% [90% compatibility limits (CL) − 8.5, − 6.3], isotonic − 8.7% (90% CL − 10.1, − 7.4), hypotonic − 6.3% (90% CL − 7.4, − 5.3) and water − 7.5% (90% CL − 8.5, − 6.4). Posterior contrast estimates relative to the smallest important effect (dPV = 0.75%) were: hypertonic-isotonic 1.2% (90% CL − 0.1, 2.6; p₊ = 0.74), hypotonic-isotonic 2.3% (90% CL 1.1, 3.5; p₊ = 0.984), water-isotonic 1.3% (90% CL 0.0, 2.5; p₊ = 0.76), hypotonic-hypertonic 1.1% (90% CL 0.1, 2.1; p₊ = 0.71), hypertonic-water 0.1% (90% CL − 0.8, 1.0; p₊ = 0.12) and hypotonic-water 1.1% (90% CL 0.1, 2.0; p₊ = 0.72). Thus, hypotonic drinks were very likely superior to isotonic and likely superior to hypertonic and water. Metabolic rate, ingestion rate, carbohydrate characteristics and electrolyte concentration were generally substantial modifiers of dPV.

Conclusion

Hypotonic carbohydrate–electrolyte drinks ingested continuously during exercise provide the greatest benefit to hydration.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-021-01558-y.

Does pain sensitivity correlate with gastrointestinal symptoms in runners? An observational survey study

Objective:

Heightened pain sensitivity is common in functional gut disorders, but no research has examined whether it corresponds to exercise-associated gastrointestinal (GI) symptoms. We sought to explore whether scores on a questionnaire of pain sensitivity would correlate with GI symptoms during running.

Design:

This is a cross-sectional study.

Subjects:

The study involves 290 (137 male, 153 female) distance runners.

Methods:

Runners completed a survey inquiring about demographic, anthropometric and training information and rated GI symptoms at rest and during runs. In addition, the Pain Sensitivity Questionnaire (PSQ) was used to quantify pain sensitivity across all items (PSQ-Total) and on items typically rated as minor (PSQ-Minor). Spearman rho correlations were utilized to assess the associations between pain sensitivity and GI symptoms. Partial correlations were used to evaluate the associations after controlling for age, gender, running experience, body mass index and sleep problems.

Results:

PSQ scores weakly correlated with several GI symptoms at rest (rho = 0.13–0.20; p < 0.05), which remained largely intact in partial correlation analyses (partial rho = 0.12–0.18). PSQ scores weakly correlated with fullness, bloating and gas during runs (rho = 0.12–0.18; p < 0.05); fullness and bloating remained significant in the partial correlation analyses (partial rho = 0.12–0.15). These results were relatively consistent for both the PSQ-Total and PSQ-Minor.

Conclusions:

Although PSQ scores only weakly correlate with certain GI symptoms among runners, the effect sizes are similar to that of other predictors of GI distress. These results suggest a minor possible role of pain sensitivity in the development of certain GI symptoms in runners.

Comparable Exogenous Carbohydrate Oxidation from Lactose or Sucrose during Exercise

PURPOSE

Ingesting readily oxidized carbohydrates (CHO) such as sucrose during exercise can improve endurance performance. Whether lactose can be utilized as a fuel source during exercise is unknown. The purpose of this study was to investigate the metabolic response to lactose ingestion during exercise, compared with sucrose or water.

METHODS

Eleven participants (age, 22 ± 4 yr; V[Combining Dot Above]O2peak, 50.9 ± 4.7 mL·min·kg) cycled at 50% Wmax for 150 min on five occasions. Participants ingested CHO beverages (lactose or sucrose; 48 g·h, 0.8 g·min) or water throughout exercise. Total substrate and exogenous CHO oxidation was estimated using indirect calorimetry and stable isotope techniques (naturally high C-abundance CHO ingestion). Naturally low C-abundance CHO trials were conducted to correct background shifts in breath CO2 production. Venous blood samples were taken to determine plasma glucose, lactate, and nonesterified fatty acid concentrations.

RESULTS

Mean exogenous CHO oxidation rates were comparable with lactose (0.56 ± 0.19 g·min) and sucrose (0.61 ± 0.10 g·min; P = 0.49) ingestion. Endogenous CHO oxidation contributed less to energy expenditure in lactose (38% ± 14%) versus water (50% ± 11%, P = 0.01) and sucrose (50% ± 7%, P ≤ 0.05). Fat oxidation was higher in lactose (42% ± 8%) than in sucrose (28% ± 6%; P ≤ 0.01); CHO conditions were lower than water (50% ± 11%; P ≤ 0.05). Plasma glucose was higher in lactose and sucrose than in water (P ≤ 0.01); plasma lactate was higher in sucrose than in water (P ≤ 0.01); plasma nonesterified fatty acids were higher in water than in sucrose (P ≤ 0.01).

CONCLUSIONS

Lactose and sucrose exhibited similar exogenous CHO oxidation rates during exercise at moderate ingestion rates. Compared with sucrose ingestion, lactose resulted in higher fat and lower endogenous CHO oxidation.

Oral carbohydrate solution cause an inflammatory response when aspirated into the lungs in mice

PURPOSE

Many studies have been published on the beneficial effects of oral carbohydrate solutions (OCS) administered prior to surgery. However, the risk of pulmonary aspiration cannot be excluded in all patients undergoing anesthesia. But, there are few studies on the safety of OCS at lung aspiration.

METHODS

Experiments were conducted with mice (Nine- to ten-week-old male BALB/c mice weighted 23-26 g). Lung aspiration was performed by intratracheal administration of OCS and its major constituents, fructose and maltodextrin. Bronchoalveolar lavage fluid (BALF) was collected 3 and 24 h after lung aspiration. The level of Tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and macrophage inflammatory protein-2 (MIP-2) were measured in BALF. The total white blood cell, neutrophil counts, wet to dry ratio and histological examination were performed in BALF and lung tissue, respectively, at 24 h after aspiration.

RESULTS

The OCS increased the level of TNF-α, IL-6 and MIP-2 at 3 h and the neutrophil count at 24 h in BALFs, compared to a phosphate-buffered saline (PBS) group. The increase in IL-6 level induced by OCS was maintained for 24 h. The OCS also increased the number of white blood cells and the percentage of neutrophils in BALFs. Compared to fructose, maltodextrin significantly increased the production of MIP-2 in BALFs. OCS and maltodextrin also increased neutrophil recruitment in lung tissue.

CONCLUSION

Aspiration of OCS may cause inflammation of the lungs. The preoperative use of OCS may require caution under specific clinical conditions, such as patients at risk of lung aspiration.

Anxiety may be a risk factor for experiencing gastrointestinal symptoms during endurance races: An observational study

Scarce research has examined the links between stress, anxiety, and gastrointestinal (GI) symptoms during competition, despite that they are positively correlated in the general population. A total of 186 endurance athletes completed the Perceived Stress Scale (PSS)-14, Anxiety Sensitivity Index (ASI)-3, and State-Trait Inventory for Cognitive and Somatic Anxiety (STICSA) before races. Afterwards, they reported the severity of in-race GI symptoms. Associations between high levels of stress and anxiety (defined as the top tertile) and GI distress (≥3 on a 0-10 scale) were examined using logistic regression. Athletes with high PSS-14 scores did not have greater odds of GI symptoms, except nausea (odds ratio [OR] = 2.21, 95% confidence interval [CI] 1.02-4.78). High scores on the STICSA-trait were associated with nausea (OR = 3.43, 95% CI 1.57-7.50) and regurgitation/reflux (OR = 3.31, 95% CI 1.26-8.73). Among a sub-sample of 125 participants that completed STICSA-state questionnaires, higher anxiety was associated with nausea (OR = 5.57, 95% CI 1.96-15.83), regurgitation/reflux (OR = 3.75, 95% CI 1.17-12.00), fullness (OR = 2.98, 95% CI 1.05-8.49), and cramping (OR = 3.99, 95% CI 1.36-11.68). The ORs remained relatively stable after adjusting for age, gender, experience, body mass index, type of race, and race duration. ASI-3 scores were not associated with symptoms. Individuals with higher levels of anxiety, especially on the morning of a race, may be prone GI distress, particularly nausea, regurgitation/reflux, and cramping.

Postexercise Glucose–Fructose Coingestion Augments Cycling Capacity During Short-Term and Overnight Recovery From Exhaustive Exercise, Compared With Isocaloric Glucose

During short-term recovery, postexercise glucose–fructose coingestion can accelerate total glycogen repletion and augment recovery of running capacity. It is unknown if this advantage translates to cycling, or to a longer (e.g., overnight) recovery. Using two experiments, the present research investigated if postexercise glucose–fructose coingestion augments exercise capacity following 4-hr (short experiment; n = 8) and 15-hr (overnight experiment; n = 8) recoveries from exhaustive exercise in trained cyclists, compared with isocaloric glucose alone. In each experiment, a glycogen depleting exercise protocol was followed by a 4-hr recovery, with ingestion of 1.5 or 1.2 g·kg−1·hr−1 carbohydrate in the short experiment (double blind) and the overnight experiment (single blind), respectively. Treatments were provided in a randomized order using a crossover design. Four or fifteen hours after the glycogen depletion protocol, participants cycled to exhaustion at 70% Wmax or 65% Wmax in the short experiment and the overnight experiment, respectively. In both experiments there was no difference in substrate oxidation or blood glucose and lactate concentrations between treatments during the exercise capacity test (trial effect, p > .05). Nevertheless, cycling capacity was greater in glucose + fructose versus glucose only in the short experiment (28.0 ± 8.4 vs. 22.8 ± 7.3 min, d = 0.65, p = .039) and the overnight experiment (35.9 ± 10.7 vs. 30.6 ± 9.2 min, d = 0.53, p = .026). This is the first study to demonstrate that postexercise glucose–fructose coingestion enhances cycling capacity following short-term (4 hr) and overnight (15 hr) recovery durations. Therefore, if multistage endurance athletes are ingesting glucose for rapid postexercise recovery then fructose containing carbohydrates may be advisable.

Mutual Interactions among Exercise, Sport Supplements and Microbiota

The adult gut microbiota contains trillions of microorganisms of thousands of different species. Only one third of gut microbiota are common to most people; the rest are specific and contribute to enhancing genetic variation. Gut microorganisms significantly affect host nutrition, metabolic function, immune system, and redox levels, and may be modulated by several environmental conditions, including physical activity and exercise. Microbiota also act like an endocrine organ and is sensitive to the homeostatic and physiological changes associated with training; in turn, exercise has been demonstrated to increase microbiota diversity, consequently improving the metabolic profile and immunological responses. On the other side, adaptation to exercise might be influenced by the individual gut microbiota that regulates the energetic balance and participates to the control of inflammatory, redox, and hydration status. Intense endurance exercise causes physiological and biochemical demands, and requires adequate measures to counteract oxidative stress, intestinal permeability, electrolyte imbalance, glycogen depletion, frequent upper respiratory tract infections, systemic inflammation and immune responses. Microbiota could be an important tool to improve overall general health, performance, and energy availability while controlling inflammation and redox levels in endurance athletes. The relationship among gut microbiota, general health, training adaptation and performance, along with a focus on sport supplements which are known to exert some influence on the microbiota, will be discussed.

'I think I'm gonna hurl': A Narrative Review of the Causes of Nausea and Vomiting in Sport

Exercise-associated gastrointestinal (GI) distress can negatively impact athletic performance and interfere with exercise training. Although there are a few universal underlying causes of GI distress, each symptom often has its own unique triggers and, therefore, its own prevention and management strategies. One of the most troubling GI symptoms an athlete can experience during training and competition is nausea/vomiting. The prevalence of nausea varies with several factors, two of the most important being exercise intensity and duration. Relatively brief, high-intensity exercise (e.g., sprinting, tempo runs) and ultra-endurance exercise are both associated with more frequent and severe nausea. The potential causes of nausea in sport are numerous and can include catecholamine secretion, hypohydration, heat stress, hyponatremia, altitude exposure, excessive fluid/food consumption, hypertonic beverage intake, pre-exercise intake of fatty- or protein-rich foods (especially in close proximity to exercise), prolonged fasting, various supplements (caffeine, sodium bicarbonate, ketones), certain drugs (antibiotics, opioids), GI infections, and competition-related anxiety. Beyond directly addressing these aforementioned causes, antiemetic drugs (e.g., ondansetron) may also be useful for alleviating nausea in some competitive situations. Given the commonness of nausea in sport and its potential impact on exercise performance, athletes and sports medicine practitioners should be aware of the origins of nausea and strategies for dealing with this troublesome gut complaint.

Carbohydrate dose influences liver and muscle glycogen oxidation and performance during prolonged exercise

This study investigated the effect of carbohydrate (CHO) dose and composition on fuel selection during exercise, specifically exogenous and endogenous (liver and muscle) CHO oxidation. Ten trained males cycled in a double‐blind randomized order on 5 occasions at 77% V˙O2max for 2 h, followed by a 30‐min time‐trial (TT) while ingesting either 60 g·h⁻¹ (LG) or 75 g·h⁻¹¹³C‐glucose (HG), 90 g·h⁻¹ (LGF) or 112.5 g·h⁻¹¹³C‐glucose‐¹³C‐fructose ([2:1] HGF) or placebo. CHO doses met or exceed reported intestinal transporter saturation for glucose and fructose. Indirect calorimetry and stable mass isotope [¹³C] tracer techniques were utilized to determine fuel use. TT performance was 93% “likely/probable” to be improved with LGF compared with the other CHO doses. Exogenous CHO oxidation was higher for LGF and HGF compared with LG and HG (ES > 1.34, P < 0.01), with the relative contribution of LGF (24.5 ± 5.3%) moderately higher than HGF (20.6 ± 6.2%, ES = 0.68). Increasing CHO dose beyond intestinal saturation increased absolute (29.2 ± 28.6 g·h⁻¹, ES = 1.28, P = 0.06) and relative muscle glycogen utilization (9.2 ± 6.9%, ES = 1.68, P = 0.014) for glucose‐fructose ingestion. Absolute muscle glycogen oxidation between LG and HG was not significantly different, but was moderately higher for HG (ES = 0.60). Liver glycogen oxidation was not significantly different between conditions, but absolute and relative contributions were moderately attenuated for LGF (19.3 ± 9.4 g·h⁻¹, 6.8 ± 3.1%) compared with HGF (30.5 ± 17.7 g·h⁻¹, 10.1 ± 4.0%, ES = 0.79 & 0.98). Total fat oxidation was suppressed in HGF compared with all other CHO conditions (ES > 0.90, P = 0.024–0.17). In conclusion, there was no linear dose response for CHO ingestion, with 90 g·h⁻¹ of glucose‐fructose being optimal in terms of TT performance and fuel selection.

Safety and performance benefits of arginine supplements for military personnel: a systematic review

CONTEXT

Dietary supplements are widely used by military personnel and civilians for promotion of health.

OBJECTIVE

The objective of this evidence-based review was to examine whether supplementation with l-arginine, in combination with caffeine and/or creatine, is safe and whether it enhances athletic performance or improves recovery from exhaustion for military personnel.

DATA SOURCES

Information from clinical trials and adverse event reports were collected from 17 databases and 5 adverse event report portals.

STUDY SELECTION

Studies and reports were included if they evaluated the safety and the putative outcomes of enhanced performance or improved recovery from exhaustion associated with the intake of arginine alone or in combination with caffeine and/or creatine in healthy adults aged 19 to 50 years.

DATA EXTRACTION

Information related to population, intervention, comparator, and outcomes was abstracted. Of the 2687 articles screened, 62 articles meeting the inclusion criteria were analyzed. Strength of evidence was assessed in terms of risk of bias, consistency, directness, and precision.

RESULTS

Most studies had few participants and suggested risk of bias that could negatively affect the results. l-Arginine supplementation provided little enhancement of athletic performance or improvements in recovery. Short-term supplementation with arginine may result in adverse gastrointestinal and cardiovascular effects. No information about the effects of arginine on the performance of military personnel was available.

CONCLUSIONS

The available information does not support the use of l-arginine, either alone or in combination with caffeine, creatine, or both, to enhance athletic performance or improve recovery from exhaustion. Given the information gaps, an evidence-based review to assess the safety or effectiveness of multi-ingredient dietary supplements was not feasible, and therefore the development of a computational model-based approach to predict the safety of multi-ingredient dietary supplements is recommended.

Timing, Optimal Dose and Intake Duration of Dietary Supplements with Evidence-Based Use in Sports Nutrition

[Purpose]

The aim of the present narrative review was to consider the evidence on the timing, optimal dose and intake duration of the main dietary supplements in sports nutrition, i.e. β-alanine, nitrate, caffeine, creatine, sodium bicarbonate, carbohydrate and protein.

[Methods]

This review article focuses on timing, optimal dose and intake duration of main dietary supplements in sports nutrition.

[Results]

This paper reviewed the evidence to determine the optimal time, efficacy doses and intake duration for sports supplements verified by scientific evidence that report a performance enhancing effect in both situation of laboratory and training settings.

[Conclusion]

Consumption of the supplements are usually suggested into 5 specific times, such as pre-exercise (nitrate, caffeine, sodium bicarbonate, carbohydrate and protein), during exercise (carbohydrate), post-exercise (creatine, carbohydrate, protein), meal time (β-alanine, creatine, sodium bicarbonate, nitrate, carbohydrate and protein), and before sleep (protein). In addition, the recommended dosing protocol for the supplements nitrate and β-alanine are fixed amounts irrespective of body weight, while dosing protocol for sodium bicarbonate, caffeine and creatine supplements are related to corrected body weight (mg/kg bw). Also, intake duration is suggested for creatine and β-alanine, being effective in chronic daily time < 2 weeks while caffeine, sodium bicarbonate are effective in acute daily time (1-3 hours). Plus, ingestion of nitrate supplement is required in both chronic daily time < 28 days and acute daily time (2- 2.5 h) prior exercise.

Effects of glucose-fructose versus glucose ingestion on stride characteristics during prolonged treadmill running

Scarce research has examined the effects of carbohydrate composition on running stride characteristics. On two occasions, 14 males and 6 females completed a 120-min sub-maximal run followed by a 4-mile time trial. Participants consumed glucose (GLU) or glucose-fructose (GLU-FRU) beverages supplying 1.3 g/min carbohydrate. Substrate use, psychological affect [Feeling Scale (FS)], and stride characteristics (stride frequency, stride length, and contact time) were assessed. Effects were expressed as Cohen's d (90% confidence limits [90% CL]). CLs for stride frequency differences at 53 min (90% CL = 0.04-0.21) and 113 min (90% CL = 0.02-0.24) did not cover 0, indicating a positive effect of GLU-FRU. However, effect sizes were small (d = 0.13) and likely-to-very-likely trivial. Energy expenditure differences at sub-maximal end were very likely trivial (d = 0.08; 90% CL = 0.00-0.17), while FS ratings were possibly higher for GLU-FRU at 50 (d = 0.19; 90% CL = -0.10-0.48) and 110 min (d = 0.16; 90% CL = -0.13-0.45). During the time trial, stride length was possibly higher with GLU-FRU (d = 0.13; 90% CL = -0.08-0.33). Glucose-fructose co-ingestion has no significant effect on stride characteristics during constant-velocity running but may result in slightly higher stride length during self-paced running.

Glucose-fructose enhances performance versus isocaloric, but not moderate, glucose

PURPOSE

The effects of glucose-and-fructose (GF) coingestion on cycling time trial (TT) performance and physiological responses to exercise were examined under postprandial conditions.

METHODS

Eight trained male cyclists (age, 25 ± 6 yr; height, 180 ± 4 cm; weight, 77 ± 9 kg; V˙O2max, 62 ± 6 mL·kg·min) completed the study. Subjects ingested either an artificially sweetened placebo (PL), a moderate-glucose beverage (MG, 1.03 g·min), a high-glucose beverage (HG, 1.55 g·min), or a GF beverage (1.55 g·min, 2:1 ratio) during approximately 3 h of exercise, including 2 h of constant-load cycling (55% Wmax, 195 ± 17 W), immediately followed by a computer-simulated 30-km TT. Physiological responses (V˙E, V˙O2, RER, HR, blood glucose level, blood lactate level, and RPE) and incidences of gastrointestinal distress were assessed during early (15-20 min), middle (55-60 min), and late exercise (115-120 min) and during the TT. Magnitude-based qualitative inferences were used to evaluate differences between treatments.

RESULTS

In comparison with that in PL (52.9 ± 3.7 min), TT performances were faster with GF (50.4 ± 2.2 min, "very likely" benefit), MG (51.1 ± 2.4 min, "likely" benefit), and HG (52.0 ± 3.7 min, "possible" benefit). GF resulted in a "likely" improvement versus HG (3.0%) and an "unclear" effect relative to MG (1.2%). MG was "possibly" beneficial versus HG (1.8%). Few incidences of GI distress were reported in any trials.

CONCLUSIONS

GF ingestion seems to enhance performance, relative to PL and HG. However, it is unclear whether GF improves performance versus moderate doses of glucose.

Saccharide Composition of Carbohydrates Consumed during an Ultra-endurance Triathlon

OBJECTIVE

Ingesting a mix of glucose and fructose during exercise increases exogenous carbohydrate oxidation while minimizing gastrointestinal (GI) distress. Several studies have suggested that a glucose-to-fructose ratio of 1.2:1 to 1:1 is optimal. No studies have quantified saccharides consumed during a nonsimulated endurance event. The aim of this investigation was to quantify saccharide sources used during an ultra-endurance triathlon and provide a resource for athletes desiring to manipulate the saccharide content of carbohydrate consumed during training and competition.

METHODS

Participant self-report and direct measurement were used to assess foods and beverages consumed during an ultra-endurance (70.3-mile) triathlon. Manufacturer-supplied information, high-performance liquid chromatography, and the US Department of Agriculture Food Database were used to quantify saccharide profiles of foods and beverages. Participants reported GI distress during the run on a 0-10 scale. A subanalysis examined associations between saccharides and GI distress among participants consuming ≥ 50 g·h(-1) of carbohydrate during the swim and cycle.

RESULTS

Fifty-four participants (43 men) used 80 foods and beverages with a unique saccharide profile. Of total carbohydrate, median proportions as glucose, fructose, and sucrose were 64%, 5%, and 10%, and only 7 foods (8.8%) had a glucose-to-fructose ratio of 1.2:1 to 1:1. The median glucose-to-fructose ratio of carbohydrate ingested was 2.9:1 (2.2:1-5.3:1). Twenty participants consumed ≥ 50 g·h(-1) of carbohydrate during the swim and cycle, and significant correlations with incident GI distress at mile 1 of the run were found for glucose (r = 0.480, p = 0.032) and fructose (r = -0.454, p = 0.044).

CONCLUSIONS

The majority of foods and beverages consumed during an ultra-endurance triathlon did not contain an optimal saccharide profile. Furthermore, glucose intake was associated with greater GI distress among participants consuming a high rate of carbohydrate.

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.

Carbohydrate-dependent, exercise-induced gastrointestinal distress

Gastrointestinal (GI) problems are a common concern of athletes during intense exercise. Ultimately, these symptoms can impair performance and possibly prevent athletes from winning or even finishing a race. The main causes of GI problems during exercise are mechanical, ischemic and nutritional factors. Among the nutritional factors, a high intake of carbohydrate and hyperosmolar solutions increases GI problems. A number of nutritional manipulations have been proposed to minimize gastrointestinal symptoms, including the use of multiple transportable carbohydrates. This type of CHO intake increases the oxidation rates and can prevent the accumulation of carbohydrate in the intestine. Glucose (6%) or glucose plus fructose (8%–10%) beverages are recommended in order to increase CHO intake while avoiding the gastric emptying delay. Training the gut with high intake of CHO may increase absorption capacity and probably prevent GI distress. CHO mouth rinse may be a good strategy to enhance performance without using GI tract in exercises lasting less than an hour. Future strategies should be investigated comparing different CHO types, doses, and concentration in exercises with the same characteristics.

Fructose-maltodextrin ratio governs exogenous and other CHO oxidation and performance

INTRODUCTION

Fructose coingested with glucose in carbohydrate (CHO) drinks increases exogenous-CHO oxidation, gut comfort, and physical performance.

PURPOSE

This study aimed to determine the effect of different fructose-maltodextrin-glucose ratios on CHO oxidation and fluid absorption while controlling for osmolality and caloricity.

METHODS

In a crossover design, 12 male cyclists rode 2 h at 57% peak power then performed 10 sprints while ingesting artificially sweetened water or three equiosmotic 11.25% CHO-salt drinks at 200 mL·15 min, comprising weighed fructose and maltodextrin-glucose in ratios of 0.5:1 (0.5 ratio), 0.8:1 (0.8 ratio), and 1.25:1 (1.25 ratio). Fluid absorption was traced with D2O, whereas C-fructose and C-maltodextrin-glucose permitted fructose and glucose oxidation rate evaluation.

RESULTS

The mean exogenous-fructose and exogenous-glucose oxidation rates were 0.27, 0.39, and 0.46 g·min and 0.65, 0.71, and 0.58 g·min in 0.5, 0.8, and 1.25 ratio drinks, representing mean oxidation efficiencies of 54%, 59%, and 55% and 65%, 85%, and 86% for fructose and glucose, respectively. With the 0.8 ratio drink, total exogenous-CHO oxidation rate was 18% (90% confidence interval, ±5%) and 5.2% (±4.6%) higher relative to 0.5 and 1.25 ratios, respectively, whereas respective differences in total exogenous-CHO oxidation efficiency were 17% (±5%) and 5.3% (±4.8%), associated with 8.6% and 7.8% (±4.2%) higher fructose oxidation efficiency. The effects of CHO ratio on water absorption were inconclusive. Mean sprint power with the 0.8 ratio drink was moderately higher than that with the 0.5 ratio (2.9%; 99% confidence interval, ±2.8%) and 1.25 ratio (3.1%; ±2.7%) drinks, with total- and endogenous-CHO oxidation rate, abdominal cramps, and drink sweetness qualifying as explanatory mechanisms.

CONCLUSIONS

Enhanced high-intensity endurance performance with a 0.8 ratio fructose-maltodextrin-glucose drink is characterized by higher exogenous-CHO oxidation efficiency and reduced endogenous-CHO oxidation. The gut-hepatic or other physiological site responsible requires further research.

Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations

This systematic review examines the efficacy of carbohydrate (CHO) supplementation on exercise performance of varying durations. Included studies utilized an all-out or endurance-based exercise protocol (no team-based performance studies) and featured randomized interventions and placebo (water-only) trial for comparison against exclusively CHO trials (no other ingredients). Of the 61 included published performance studies (n = 679 subjects), 82% showed statistically significant performance benefits (n = 50 studies), with 18% showing no change compared with placebo. There was a significant (p = 0.0036) correlative relationship between increasing total exercise time and the subsequent percent increase in performance with CHO intake versus placebo. While not mutually exclusive, the primary mechanism(s) for performance enhancement likely differs depending on the duration of the exercise. In short duration exercise situations (∼1 h), oral receptor exposure to CHO, via either mouthwash or oral consumption (with enough oral contact time), which then stimulates the pleasure and reward centers of the brain, provide a central nervous system-based mechanism for enhanced performance. Thus, the type and (or) amount of CHO and its ability to be absorbed and oxidized appear completely irrelevant to enhancing performance in short duration exercise situations. For longer duration exercise (>2 h), where muscle glycogen stores are stressed, the primary mechanism by which carbohydrate supplementation enhances performance is via high rates of CHO delivery (>90 g/h), resulting in high rates of CHO oxidation. Use of multiple transportable carbohydrates (glucose:fructose) are beneficial in prolonged exercise, although individual recommendations for athletes should be tailored according to each athlete's individual tolerance.

Assessing a commercially available sports drink on exogenous carbohydrate oxidation, fluid delivery and sustained exercise performance

Background

Whilst exogenous carbohydrate oxidation (CHO_EXO) is influenced by mono- and disaccharide combinations, debate exists whether such beverages enhance fluid delivery and exercise performance. Therefore, this study aimed to ascertain CHO_EXO, fluid delivery and performance times of a commercially available maltodextrin/ fructose beverage in comparison to an isocaloric maltodextrin beverage and placebo.

Methods

Fourteen club level cyclists (age: 31.79 ± 10.02 years; height: 1.79 ± 0.06 m; weight: 73.69 ± 9.24 kg; VO_2max: 60.38 ± 9.36 mL · kg^·-1 min^-1) performed three trials involving 2.5 hours continuous exercise at 50% maximum power output (W_max: 176.71 ± 25.92 W) followed by a 60 km cycling performance test. Throughout each trial, athletes were randomly assigned, in a double-blind manner, either: (1) 1.1 g · min^-1 maltodextrin + 0.6 g · min^-1 fructose (MD + F), (2) 1.7 g · min^-1 of maltodextrin (MD) or (3) flavoured water (P). In addition, the test beverage at 60 minutes contained 5.0 g of deuterium oxide (²H₂O) to assess quantification of fluid delivery. Expired air samples were analysed for CHO_EXO according to the ¹³C/¹²C ratio method using gas chromatography continuous flow isotope ratio mass spectrometry.

Results

Peak CHO_EXO was significantly greater in the final 30 minutes of submaximal exercise with MD + F and MD compared to P (1.45 ± 0.09 g · min^-1, 1.07 ± 0.03 g · min^-1and 0.00 ± 0.01 g · min^-1 respectively, P < 0.0001), and significantly greater for MD + F compared to MD (P = 0.005). The overall appearance of ²H₂O in plasma was significantly greater in both P and MD + F compared to MD (100.27 ± 3.57 ppm, 92.57 ± 2.94 ppm and 78.18 ± 4.07 ppm respectively, P < 0.003). There was no significant difference in fluid delivery between P and MD + F (P = 0.078). Performance times significantly improved with MD + F compared with both MD (by 7 min 22 s ± 1 min 56 s, or 7.2%) and P (by 6 min 35 s ± 2 min 33 s, or 6.5%, P < 0.05) over 60 km.

Conclusions

A commercially available maltodextrin-fructose beverage improves CHO_EXO and fluid delivery, which may benefit individuals during sustained moderate intensity exercise. The greater CHO_EXO observed when consuming a maltodextrin-fructose beverage may support improved performance times.

The ingestion of protein with a maltodextrin and fructose beverage on substrate utilisation and exercise performance

The study investigated the ingestion of maltodextrin, fructose, and protein on exogenous carbohydrate oxidation (CHOEXO) and exercise performance. Seven trained cyclists and (or) triathletes (maximal oxygen consumption, 59.20 ± 9.00 mL·kg−1·min−1) performed 3 exercise trials that consisted of 150 min of cycling at 50% maximal power output (160 ± 11 W), followed by a 60-km time trial. One of 3 beverages were randomly assigned during each trial and consumed at 15-min intervals: (i) 0.84 g·min−1 maltodextrin + 0.52 g·min−1 fructose + 0.34 g·min−1 protein (MD+F+P); (ii) 1.10 g·min−1 maltodextrin + 0.60 g·min−1 fructose (MD+F); or (iii) 1.70 g·min−1 maltodextrin (MD). CHOEXO and fuel utilisation were assessed via measurement of expired air 13C content and indirect calorimetry, respectively. Mean total CHO oxidation (CHOTOT) rates were 2.35 ± 0.18, 2.76 ± 0.08, and 2.61 ± 0.17 g·min−1 with MD, MD+F, and MD+F+P, respectively, although not significantly different. Peak CHOEXO rates with MD+F were significantly greater by 41.4% (p = 0.001) and 45.4% (p = 0.0001) compared with MD+F+P and MD, respectively (1.57 ± 0.22 g·min−1, 1.11 ± 0.08 g·min−1, and 1.08 ± 0.11 g·min−1, respectively). Performance times were 2.2% and 5.0% faster with MD+F compared with MD+F+P and MD, respectively; however, they were not statistically significant. Ingestion of an MD−fructose−protein commercial sports beverage significantly reduced peak and mean CHOEXO rates compared with MD+F, but did not significantly influence CHOTOT. The addition of protein to an MD+F beverage did not enhance performance times.

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.

Composite versus single transportable carbohydrate solution enhances race and laboratory cycling performance

When ingested at high rates (1.8-2.4 g·min(-1)) in concentrated solutions, carbohydrates absorbed by multiple (e.g., fructose and glucose) vs. single intestinal transporters can increase exogenous carbohydrate oxidation and endurance performance, but their effect when ingested at lower, more realistic, rates during intermittent high-intensity endurance competition and trials is unknown. Trained cyclists participated in two independent randomized crossover investigations comprising mountain-bike races (average 141 min; n = 10) and laboratory trials (94-min high-intensity intervals followed by 10 maximal sprints; n = 16). Solutions ingested during exercise contained electrolytes and fructose + maltodextrin or glucose + maltodextrin in 1:2 ratio ingested, on average, at 1.2 g carbohydrate·kg(-1)·h(-1). Exertion, muscle fatigue, and gastrointestinal discomfort were recorded. Data were analysed using mixed models with gastrointestinal discomfort as a mechanism covariate; inferences were made against substantiveness thresholds (1.2% for performance) and standardized difference. The fructose-maltodextrin solution substantially reduced race time (-1.8%; 90% confidence interval = ±1.8%) and abdominal cramps (-8.1 on a 0-100 scale; ±6.6). After accounting for gastrointestinal discomfort, the effect of the fructose-maltodextrin solution on lap time was reduced (-1.1%; ±2.4%), suggesting that gastrointestinal discomfort explained part of the effect of fructose-maltodextrin on performance. In the laboratory, mean sprint power was enhanced (1.4%; ±0.8%) with fructose-maltodextrin, but the effect on peak power was unclear (0.7%; ±1.5%). Adjusting out gastrointestinal discomfort augmented the fructose-maltodextrin effect on mean (2.6%; ±1.9%) and peak (2.5%; ±3.0%) power. Ingestion of multiple transportable vs. single transportable carbohydrates enhanced mountain-bike race and high-intensity laboratory cycling performance, with inconsistent but not irreconcilable effects of gut discomfort as a possible mediating mechanism.

L-Arginine but not L-glutamine likely increases exogenous carbohydrate oxidation during endurance exercise

The addition of L-arginine or L-glutamine to glucose-electrolyte solutions can increase intestinal water, glucose, and sodium absorption in rats and humans. We evaluated the utility of L-arginine and L-glutamine in energy-rehydration beverages through assessment of exogenous glucose oxidation and perceptions of exertion and gastrointestinal distress during endurance exercise. Eight cyclists rode 150 min at 50% of peak power on four occasions while ingesting solutions at a rate of 150 mL 15 min(-1) that contained (13)C-enriched glucose (266 mmol L(-1)) and sodium citrate ([Na(+)] 60 mmol L(-1)), and either: 4.25 mmol L(-1) L-arginine or 45 mmol L(-1) L-glutamine, and as controls glucose only or no glucose. Relative to glucose only, L-arginine invoked a likely 12% increase in exogenous glucose oxidation (90% confidence limits: ± 8%); however, the effect of L-glutamine was possibly trivial (4.5 ± 7.3%). L-Arginine also led to very likely small reductions in endogenous fat oxidation rate relative to glucose (12 ± 4%) and L-glutamine (14 ± 4%), and relative to no glucose, likely reductions in exercise oxygen consumption (2.6 ± 1.5%) and plasma lactate concentration (0.20 ± 0.16 mmol L(-1)). Effects on endogenous and total carbohydrate oxidation were inconsequential. Compared with glucose only, L-arginine and L-glutamine caused likely small-moderate effect size increases in perceptions of stomach fullness, abdominal cramp, exertion, and muscle tiredness during exercise. Addition of L-arginine to a glucose and electrolyte solution increases the oxidation of exogenous glucose and decreases the oxygen cost of exercise, although the mechanisms responsible and impact on endurance performance require further investigation. However, L-arginine also increases subjective feelings of gastrointestinal distress, which may attenuate its other benefits.

Carbohydrate ingestion during endurance exercise improves performance in adults

This study was a systematic review with meta-analysis examining the efficacy of carbohydrate (CHO) ingestion compared with placebo (PLA) on endurance exercise performance in adults. Relevant databases were searched to January 2011. Included studies were PLA-controlled, randomized, crossover designs in which CHO ingestion not exceeding 8% and between 30 and 80 g/h during exercise of ≥1 h was evaluated via time trial (TT) or exercise time to exhaustion (TTE). The between-trial standardized mean differences [effect size (ES)] and pooled estimates of the effect of CHO ingestion were calculated. Of the 41,175 studies from the initial search, 50 were included. The ES for submaximal exercise followed by TT was significant (ES = 0.53; 95% CI = 0.37-0.69; P < 0.001) as was the ES for TT (ES = 0.30; 95% CI = 0.07-0.53; P = 0.011). The weighted mean improvement in exercise performance favored CHO ingestion (7.5 and 2.0%, respectively). TTE (ES = 0.47; 95% CI = 0.32-0.62; P < 0.001) and submaximal exercise followed by TTE (ES = 0.44; 95% CI = 0.08-0.80; P = 0.017) also showed significant effects, with weighted mean improvements of 15.1 and 54.2%, respectively, with CHO ingestion. Similar trends were evident for subanalyses of studies using only male or trained participants, for exercise of 1-3 h duration, and where CHO and PLA beverages were matched for electrolyte content. The data support that ingestion of CHO between 30 and 80 g/h enhances endurance exercise performance in adults.