Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance

A key goal of pre-exercise nutritional strategies is to maximize carbohydrate stores, thereby minimizing the ergolytic effects of carbohydrate depletion. Increased dietary carbohydrate intake in the days before competition increases muscle glycogen levels and enhances exercise performance in endurance events lasting 90 min or more. Ingestion of carbohydrate 3-4 h before exercise increases liver and muscle glycogen and enhances subsequent endurance exercise performance. The effects of carbohydrate ingestion on blood glucose and free fatty acid concentrations and carbohydrate oxidation during exercise persist for at least 6 h. Although an increase in plasma insulin following carbohydrate ingestion in the hour before exercise inhibits lipolysis and liver glucose output, and can lead to transient hypoglycaemia during subsequent exercise in susceptible individuals, there is no convincing evidence that this is always associated with impaired exercise performance. However, individual experience should inform individual practice. Interventions to increase fat availability before exercise have been shown to reduce carbohydrate utilization during exercise, but do not appear to have ergogenic benefits.     

Optimization of insulin-mediated creatine retention during creatine feeding in humans

Abstract

The aim of this study was to determine whether creatine ingested in combination with relatively small quantities of essential amino acids, simple sugars, and protein would stimulate insulin release and augment whole-body creatine retention to the same extent as a large bolus of simple sugars. Seven young, healthy males underwent three randomized, 3-day experimental trials. Each day, 24-h urine collections were made, and on the second day participants received 5 g creatine + water (creatine trial), 5 g creatine + ～95 g dextrose (creatine + carbohydrate) or 5 g creatine + 14 g protein hydrolysate, 7 g leucine, 7 g phenylalanine, and 57 g dextrose (creatine + protein, amino acids, and carbohydrate) via naso-gastric tube at three equally spaced intervals. Blood samples were collected at predetermined intervals after the first and third naso-gastric bolus. After administration of the first and third bolus, serum insulin concentration was increased by 15 min (P < 0.05) in the creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate trials compared with creatine alone, and plasma creatine increased more following creatine alone (15 min, P < 0.05) than in the creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate trials. Urinary creatine excretion was greater with creatine alone (P < 0.05) than with creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate. Administration of creatine + protein, amino acids, and carbohydrate can stimulate insulin release and augment whole-body creatine retention to the same extent as when larger quantities of simple sugars are ingested.     

Influence of pre-exercise glucose ingestion of two concentrations on paraplegic athletes

In this study, we assessed the influence that pre-exercise glucose ingestion of two concentrations has on the physiological responses of paraplegic athletes. Eight men with paraplegia ingested a drink containing 4% (low) or 11% (high) carbohydrate in a randomized double-blind crossover design, 20 min before exercise. The participants performed wheelchair exercise at 65% of peak oxygen uptake for 1 h followed by a 20 min performance test. During both trials, the physiological responses were similar and indicated steady-state exercise. At the onset of exercise, blood glucose concentrations in both trials increased after carbohydrate ingestion (P < 0.05) before returning to resting values after 20 min of exercise and there were no differences between trials. Free fatty acid concentrations increased from rest to 1 h of exercise in both trials, with a greater increase during the low carbohydrate trial that led to a difference in free fatty acids between trials at the end of the 1 h tests (P < 0.05). There was a tendency for the performance distances and power outputs achieved during the high carbohydrate trial to be greater than those achieved during the low carbohydrate trial (P= 0.08). In conclusion, when paraplegic athletes ingested low and high carbohydrate drinks before exercise, the decline in blood glucose concentrations was similar. The tendency for higher blood glucose concentrations, respiratory exchange ratios and power outputs and lower free fatty acid concentrations (P < 0.05) during the high carbohydrate trial suggests that a higher concentration of carbohydrate in a sports drink might be a better choice for paraplegic athletes.     

Carbohydrate ingestion improves endurance performance during a 1h simulated cycling time trial

This study examined the effect of carbohydrate ingestion on metabolic and performance-related responses during and after a simulated 1h cycling time trial. Eight trained male cyclists (VO 2 peak = 66.5ml kg -1 min -1 ) rode their own bicycles mounted on a windload simulator to imitate real riding conditions. At a self-selected maximal pace, the cyclists performed two 1h rides (separated by 7 days) and were fed either an 8% carbohydrate or placebo solution. The beverages were administered 25 min before (4.5ml kg -1 ) and at the end (4.5ml kg -1 ) of the ride. With carbohydrate feeding, plasma glucose tended (P = 0.21) to rise before the time trial. Compared with rest, the plasma glucose concentration decreased significantly (P < 0.05) at the end of both rides, with no statistically significant difference being observed between treatments. Thereafter, plasma glucose increased significantly (P < 0.05) at 15 and 30 min into recovery, and was significantly higher at 30 min during the carbohydrate trial compared with the placebo trial. No significant changes in plasma free fatty acids were observed during the ride. However, a significant increase (P < 0.05) in free fatty acids was found at 15 and 30 min into recovery, with no difference between trials. Mean power output was significantly (P < 0.05) greater during the carbohydrate compared with the placebo trial (mean - S.E.: 277-3 and 269-3W, respectively). The greater distance covered in the carbohydrate compared with the placebo trial (41.5-1.06 and 41.0–1.06km, respectively; P < 0.05) was equivalent to a 44s improvement. We conclude that pre-exercise carbohydrate ingestion significantly increases endurance performance in trained cyclists during a 1h simulated time trial. Although the mechanism for this enhancement in performance with carbohydrate ingestion cannot be surmised from the present results, it could be related to a higher rate of carbohydrate oxidation, or to favourable effects of carbohydrate ingestion on the central component of fatigue.     

Skeletal muscle glycogen concentration and metabolic responses following a high glycaemic carbohydrate breakfast

The purpose of this study was to examine the influence of a carbohydrate-rich meal on post-prandial metabolic responses and skeletal muscle glycogen concentration. After an overnight fast, eight male recreational/club endurance runners ingested a carbohydrate (CHO) meal (2.5 g CHO x kg(-1) body mass) and biopsies were obtained from the vastus lateralis muscle before and 3 h after the meal. Ingestion of the meal resulted in a 10.6 +/- 2.5% (P < 0.05) increase in muscle glycogen concentration (pre-meal vs post-meal: 314.0 +/- 33.9 vs 347.3 +/- 31.3 mmol x kg(-1) dry weight). Three hours after ingestion, mean serum insulin concentrations had not returned to pre-feeding values (0 min vs 180 min: 45 +/- 4 vs 143 +/- 21 pmol x l(-1)). On a separate occasion, six similar individuals ingested the meal or fasted for a further 3 h during which time expired air samples were collected to estimate the amount of carbohydrate oxidized over the 3 h post-prandial period. It was estimated that about 20% of the carbohydrate consumed was converted into muscle glycogen, and about 12 % was oxidized. We conclude that a meal providing 2.5 g CHO x kg(-1) body mass can increase muscle glycogen stores 3 h after ingestion. However, an estimated 67% of the carbohydrate ingested was unaccounted for and this may have been stored as liver glycogen and/or still be in the gastrointestinal tract.     

Nutritional needs of elite endurance athletes. Part I: Carbohydrate and fluid requirements

Abstract

Both carbohydrate depletion and dehydration have been shown to decrease performance whilst severe dehydration can also cause adverse health effects. Therefore carbohydrate and fluid requirements are increased with exercise. Ingestion of 200–300?g of CHO 3–4?h prior to exercise is an effective strategy in order to meet daily CHO demands and increase CHO availability during the subsequent exercise period. There is little evidence that CHO during the hour immediately prior to exercise has adverse effects such as rebound hypoglycaemia. CHO ingestion during exercise has been shown to improve performance as measured by enhanced work output or decreased exercise time to complete a fixed amount of work. Recent studies have demonstrated that exogenous CHO oxidation rates can be increased by ingesting combinations of CHO that use different intestinal CHO transporters. After exercise maximal muscle glycogen re-synthesis rates can be achieved by ingesting CHO at a rate of ～1.2?g/kg/h, in relatively frequent (e.g., 15–30?min) intervals for up to 5?h following exercise. Protein amino acid mixtures may increase glycogen synthesis further but only if relatively small amounts of CHO are ingested.

Hypohydration and hyperthermia alone have negative effects on performance but their combination is particularly serious, both in terms of performance and health. Dehydration can be prevented by fluid ingestion pre exercise and during exercise. Because of large individual differences it is difficult to individualise the advice. Perhaps the best guidance for athletes is to weigh themselves to assess fluid losses during training and racing and limit weight losses to 1% during exercise lasting longer than 1.5?h. Excessive fluid intake has been associated with hyponatremia. Post exercise the volume of fluid ingested and sodium intake are important determinants of rehydration.     

Cow's milk as a post-exercise recovery drink: implications for performance and health

Abstract

Post-exercise recovery is a multi-facetted process that will vary depending on the nature of the exercise, the time between exercise sessions and the goals of the exerciser. From a nutritional perspective, the main considerations are: (1) optimisation of muscle protein turnover; (2) glycogen resynthesis; (3) rehydration; (4) management of muscle soreness; (5) appropriate management of energy balance. Milk is approximately isotonic (osmolality of 280–290?mosmol/kg), and the mixture of high quality protein, carbohydrate, water and micronutrients (particularly sodium) make it uniquely suitable as a post-exercise recovery drink in many exercise scenarios. Research has shown that ingestion of milk post-exercise has the potential to beneficially impact both acute recovery and chronic training adaptation. Milk augments post-exercise muscle protein synthesis and rehydration, can contribute to post-exercise glycogen resynthesis, and attenuates post-exercise muscle soreness/function losses. For these aspects of recovery, milk is at least comparable and often out performs most commercially available recovery drinks, but is available at a fraction of the cost, making it a cheap and easy option to facilitate post-exercise recovery. Milk ingestion post-exercise has also been shown to attenuate subsequent energy intake and may lead to more favourable body composition changes with exercise training. This means that those exercising for weight management purposes might be able to beneficially influence post-exercise recovery, whilst maintaining the energy deficit created by exercise.     

Nutritional needs of elite endurance athletes. Part II: Dietary protein and the potential role of caffeine and creatine

Abstract

Amino acids contribute between 2–8% of the energy needs during endurance exercise. Endurance exercise training leads to an adaptive reduction in the oxidation of amino acids at the same absolute exercise intensity, however, the capacity to oxidize amino acids goes up due to the increase in the total amount of the rate limiting enzyme, branched chain 2-oxo-acid dehydrogenase. There appears to be a modest increase (range?=?12–95%) in protein requirements only for very well trained athletes who are actively training. Although the majority of athletes will have ample dietary protein to meet any increased need, those on a hypoenergetic diet or during extreme periods of physical stress may need dietary manipulation to accommodate the need. Caffeine is a trimethylxanthine derivative that is common in many foods and beverages. The consumption of caffeine (3–7 mg/kg) prior to endurance exercise improves performance for habitual and non-habitual consumers. The ergogenic effect is likely due to a direct effect on muscle contractility and not via an enhancement of fatty acid oxidation. Creatine is important in intra-cellular energy shuttling and in cellular fluid regulation. Creatine monohydrate supplementation (20 g/d X 3–5 days) increases fat-free mass, improves muscle strength during repetitive high intensity contractions and increases fat-free mass accumulation and strength during a period of weight training. Given the increase in weight, there are likely neutral or even performance reducing effects in sports that are influenced by body mass (i.e., running, hill climbing cycling).     

A combined insulin reduction and carbohydrate feeding strategy 30 min before running best preserves blood glucose concentration after exercise through improved fuel oxidation in type 1 diabetes mellitus

In this study, we examined the glycaemic and fuel oxidation responses to alterations in the timing of a low glycaemic index carbohydrate and 75% reduced insulin dose, prior to running, in type 1 diabetes individuals. After carbohydrate (75 g isomaltulose) and insulin administration, the seven participants rested for 30 min, 60 min, 90 min or 120 min (conditions 30MIN, 60MIN, 90MIN, and 120MIN, respectively) before completing 45 min of running at 70% peak oxygen uptake. Carbohydrate and lipid oxidation rates were monitored during exercise and blood glucose and insulin were measured before and for 3 h after exercise. Data were analysed using repeated-measures analysis of variance. Pre-exercise blood glucose concentrations were lower for 30MIN compared with 120MIN (P < 0.05), but insulin concentrations were similar. Exercising carbohydrate and lipid oxidation rates were lower and greater, respectively, for 30MIN compared with 120MIN (P < 0.05). The drop in blood glucose during exercise was less for 30MIN (3.7 mmol · l(-1), s(x) = 0.4) compared with 120MIN (6.4 mmol · l(-1), s(x) = 0.3) (P = 0.02). For 60 min post-exercise, blood glucose concentrations were higher for 30MIN compared with 120MIN (P < 0.05). There were no cases of hypoglycaemia in the 30MIN condition, one case in the 60MIN condition, two in the 90MIN condition, and five in the 120MIN condition. In conclusion, a low glycaemic index carbohydrate and reduced insulin dose administered 30 min before running improves pre- and post-exercise blood glucose responses in type 1 diabetes.     

The influence of carbohydrate and protein ingestion during recovery from prolonged exercise on subsequent endurance performance

Ingesting carbohydrate plus protein following prolonged exercise may restore exercise capacity more effectively than ingestion of carbohydrate alone. The objective of the present study was to determine whether this potential benefit is a consequence of the protein fraction per se or simply due to the additional energy it provides. Six active males participated in three trials, each involving a 90-min treadmill run at 70% maximal oxygen uptake (run 1) followed by a 4-h recovery. At 30-min intervals during recovery, participants ingested solutions containing: (1) 0.8 g carbohydrate x kg body mass (BM)(-1) h(-1) plus 0.3 g kg(-1) h(-1) of whey protein isolate (CHO-PRO); (2) 0.8 g carbohydrate x kg BM(-1) h(-1) (CHO); or (3) 1.1 g carbohydrate x kg BM(-1) h(-1) (CHO-CHO). The latter two solutions matched the CHO-PRO solution for carbohydrate and for energy, respectively. Following recovery, participants ran to exhaustion at 70% maximal oxygen uptake (run 2). Exercise capacity during run 2 was greater following ingestion of CHO-PRO and CHO-CHO than following ingestion of CHO (P< or = 0.05) with no significant difference between the CHO-PRO and CHO-CHO treatments. In conclusion, increasing the energy content of these recovery solutions extended run time to exhaustion, irrespective of whether the additional energy originated from sucrose or whey protein isolate.     

Fluid and fuel intake during exercise

The amounts of water, carbohydrate and salt that athletes are advised to ingest during exercise are based upon their effectiveness in attenuating both fatigue as well as illness due to hyperthermia, dehydration or hyperhydration. When possible, fluid should be ingested at rates that most closely match sweating rate. When that is not possible or practical or sufficiently ergogenic, some athletes might tolerate body water losses amounting to 2% of body weight without significant risk to physical well-being or performance when the environment is cold (e.g. 5-10 degrees C) or temperate (e.g. 21-22 degrees C). However, when exercising in a hot environment ( > 30 degrees C), dehydration by 2% of body weight impairs absolute power production and predisposes individuals to heat injury. Fluid should not be ingested at rates in excess of sweating rate and thus body water and weight should not increase during exercise. Fatigue can be reduced by adding carbohydrate to the fluids consumed so that 30-60 g of rapidly absorbed carbohydrate are ingested throughout each hour of an athletic event. Furthermore, sodium should be included in fluids consumed during exercise lasting longer than 2 h or by individuals during any event that stimulates heavy sodium loss (more than 3-4 g of sodium). Athletes do not benefit by ingesting glycerol, amino acids or alleged precursors of neurotransmitter. Ingestion of other substances during exercise, with the possible exception of caffeine, is discouraged. Athletes will benefit the most by tailoring their individual needs for water, carbohydrate and salt to the specific challenges of their sport, especially considering the environment's impact on sweating and heat stress.     

The addition of whey protein to a carbohydrate–electrolyte drink does not influence post-exercise rehydration

The addition of whey protein to a carbohydrate–electrolyte drink has been shown to enhance post-exercise rehydration when a volume below that recommended for full fluid balance restoration is provided. We investigated if this held true when volumes sufficient to restore fluid balance were consumed and if differences might be explained by changes in plasma albumin content. Sixteen participants lost ~1.9% of their pre-exercise body mass by cycling in the heat and rehydrated with 150% of body mass lost with either a 60 g · L^?1 carbohydrate drink (CHO) or a 60 g · L^?1 carbohydrate, 20 g · L^?1 whey protein isolate drink (CHO-P). Urine and blood samples were collected pre-exercise, post-exercise, post-rehydration and every hour for 4 h post-rehydration. There was no difference between trials for total urine production (CHO 1057 ± 319 mL; CHO-P 970 ± 334 mL; P = 0.209), drink retention (CHO 51 ± 12%; CHO-P 55 ± 15%; P = 0.195) or net fluid balance (CHO ?393 ± 272 mL; CHO-P ?307 ± 331 mL; P = 0.284). Plasma albumin content relative to pre-exercise was increased from 2 to 4 h during CHO-P only. These results demonstrate that the addition of whey protein isolate to a carbohydrate–electrolyte drink neither enhances nor inhibits rehydration. Therefore, where post-exercise protein ingestion might benefit recovery, this can be consumed without effecting rehydration.     

Post-exercise ingestion of a unique, high molecular weight glucose polymer solution improves performance during a subsequent bout of cycling exercise

The aim of the present study was to determine the effect of post-exercise ingestion of a unique, high molecular weight glucose polymer solution, known to augment gastric emptying and post-exercise muscle glycogen re-synthesis, on performance during a subsequent bout of intense exercise. On three randomized visits, eight healthy men cycled to exhaustion at 73.0% (s = 1.3) maximal oxygen uptake (90 min, s = 15). Immediately after this, participants consumed a one-litre solution containing sugar-free flavoured water (control), 100 g of a low molecular weight glucose polymer or 100 g of a very high molecular weight glucose polymer, and rested on a bed for 2 h. After recovery, a 15-min time-trial was performed on a cycle ergometer, during which work output was determined. Post-exercise ingestion of the very high molecular weight glucose polymer solution resulted in faster and greater increases in blood glucose (P < 0.001) and serum insulin (P < 0.01) concentrations than the low molecular weight glucose polymer solution, and greater work output during the 15-min time-trial (164.1 kJ, s = 21.1) than both the sugar-free flavoured water (137.5 kJ, s = 24.2; P < 0.05) and the low molecular weight glucose polymer (149.4 kJ, s = 21.8; P < 0.05) solutions. These findings could be of practical importance for athletes wishing to optimize performance by facilitating rapid re-synthesis of the muscle glycogen store during recovery following prolonged sub-maximal exercise.     

Influence of ingesting a carbohydrate‐electrolyte solution on endurance capacity during intermittent,high‐intensity shuttle running

The aim of this study was to examine the effects of ingesting a carbohydrate‐electrolyte solution on endurance capacity during a prolonged intermittent, high‐intensity shuttle running test (PIHSRT). Nine trained male games players performed two exercise trials, 7 days apart. On each occasion, they completed 75 min exercise, comprising of five 15‐min periods of intermittent running, consisting of sprinting, interspersed with periods of jogging and walking (Part A), followed by intermittent running to fatigue (Part B). The subjects were randomly allocated either a 6.9% carbohydrate‐electrolyte solution (CHO) or a non‐carbohydrate placebo (CON) immediately prior to exercise (5 ml kg^‐1 body mass) and every 15 min thereafter (2 ml kg^‐1 body mass). Venous blood samples were obtained at rest, during and after each PIHSRT for the determination of glucose, lactate, plasma free fatty acid, glycerol, ammonia, and serum insulin and electrolyte concentrations. During Part B, the subjects were able to continue running longer when fed CHO (CHO = 8.9 ± 1.5 min vs CON = 6.7 ± 1.0 min; P < 0.05) (mean ± s.e.m.). These results show that drinking a carbohydrate‐electrolyte solution improves endurance running capacity during prolonged intermittent exercise.     

Implicit overcompensation: The influence of negative self-instructions on performance of a self-paced motor task

Abstract

This study sought to compare the time course changes in oxidative state and glycemic behavior when glucose or glucose plus fructose are consumed before endurance and strength exercise. After two weeks on a controlled diet, 20 physically trained males ingested an oral dose of glucose or glucose plus fructose, 15 min before starting a moderate-intensity 30-min session of endurance or strength exercise. The combination resulted in four randomized interventions: glucose or glucose plus fructose + endurance exercise and glucose or glucose plus fructose + strength exercise, which were implemented consecutively in random order at 1-week intervals. Plasma concentration of lipoperoxides, oxidized LDL, reduced glutathione, catalase and glycemia were determined at baseline, during exercise and acute recovery. Following the ingestion of glucose plus fructose, lipoperoxides, catalase and reduced glutathione depletion were significantly higher than following consumption of glucose, for both endurance and strength exercise (P < 0.05). Oxidized LDL-c was higher after glucose plus fructose than after glucose alone in endurance exercise (P < 0.05). There was no difference in the glycemic peak between glucose plus fructose and glucose ingestion in endurance exercise trials. In strength exercise, the post-absorptive glycemic peak was less when the participants ingested glucose plus fructose than glucose (P < 0.05), and a second peak was found in the recovery phase of this group (P < 0.05). In conclusion, the addition of fructose to a pre-exercise glucose supplement triggers oxidative stress.     

Skeletal muscle glycogen concentration and metabolic responses following a high glycaemic carbohydrate breakfast

The purpose of this study was to examine the influence of a carbohydrate-rich meal on post-prandial metabolic responses and skeletal muscle glycogen concentration. After an overnight fast, eight male recreational/club endurance runners ingested a carbohydrate (CHO) meal (2.5 g CHO?·?kg^?1 body mass) and biopsies were obtained from the vastus lateralis muscle before and 3 h after the meal. Ingestion of the meal resulted in a 10.6?±?2.5% (P?<?0.05) increase in muscle glycogen concentration (pre-meal vs post-meal: 314.0?±?33.9 vs 347.3?±?31.3 mmol?·?kg^?1 dry weight). Three hours after ingestion, mean serum insulin concentrations had not returned to pre-feeding values (0 min vs 180 min: 45?±?4 vs 143?±?21 pmol?·?l^?1). On a separate occasion, six similar individuals ingested the meal or fasted for a further 3 h during which time expired air samples were collected to estimate the amount of carbohydrate oxidized over the 3 h post-prandial period. It was estimated that about 20% of the carbohydrate consumed was converted into muscle glycogen, and about 12 % was oxidized. We conclude that a meal providing 2.5 g CHO?·?kg^?1 body mass can increase muscle glycogen stores 3 h after ingestion. However, an estimated 67% of the carbohydrate ingested was unaccounted for and this may have been stored as liver glycogen and/or still be in the gastrointestinal tract.     

Carbohydrate and carbohydrate + protein for cycling time-trial performance

Carbohydrate intake during endurance exercise delays the onset of fatigue and improves performance. Two recent cycling studies have reported increased time to exhaustion when protein is ingested together with carbohydrate. The purpose of the present study was to test the hypothesis that ingestion of a carbohydrate + protein beverage will lead to significant improvements in cycling time-trial performance relative to placebo and carbohydrate alone. Thirteen cyclists completed 120 min of constant-load ergometer cycling. Thereafter, participants performed a time-trial in which they completed a set amount of work (7 kJ kg(-1)) as quickly as possible. Participants completed four experimental trials, the first for familiarization and then three randomized, double-blind treatments consisting of a placebo, carbohydrate, and carbohydrate + protein. Participants received 250 ml of beverage every 15 min during the constant-load ride. Time-trial performance for carbohydrate (37.1 min, s = 3.8) was significantly (P < 0.05) faster than placebo (39.7 min, s = 4.6). Time-trial performance for carbohydrate + protein (38.8 min, s = 5.5) was not significantly different from either placebo or carbohydrate. Ingestion of a carbohydrate beverage during two hours of constant-load cycling significantly enhanced subsequent time-trial performance compared with placebo. The carbohydrate + protein beverage provided no additional performance benefit.     

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 gel ingestion during running in the heat on markers of gastrointestinal distress

The purpose of this study is to measure the effects of carbohydrate ingestion during exercise in the heat by measuring markers of gastrointestinal damage and inflammation. Methods: Active subjects (n?=?7) completed two 60-min running trials in a heated environment (70% VO₂max, 30°C). At minute 20 of exercise, subjects consumed a carbohydrate gel (Cho) (27?g), or a non-carbohydrate placebo (nCho). Plasma endotoxin, I-FABP, TNF-α, IL-6, IL-1β, IL-10, and MCP-1 were measured pre-exercise, 20-min post-exercise, and again 2-h, and 4-h post-exercise. Results: Endotoxin increased 20-min post-exercise compared to pre in the Cho trial only (p?=?.03). I-FABP levels increased 20-min post-exercise in the Cho trial only compared to pre-exercise (p?=?.003). I-FABP levels were also increased in Cho trial 20-min post-exercise when compared to same time point in the nCho trial (p?=?.032). TNF-α increased 20-min post-exercise in the Cho trial only compared to pre (p?=?.03). Plasma IL-6 concentration increased 20-min post-exercise when compared to pre in both the Cho (p?=?.002) and nCho (p?=?.009), but remained elevated at the 2-h time point in the nCho trial (p?=?.03). I-FABP and several plasma cytokines (TNF-α, MCP-1, Il-6) returned to baseline sooner in the Cho trial. Conclusions: Ingestion of carbohydrate gel during exercise in the heat enhances markers of gastrointestinal wall damage.     

Effect of water ingestion on endurance capacity during prolonged running

This study examined the influence of water ingestion on endurance capacity during submaximal treadmill running. Four men and four women with a mean (± S.E.) age of 21.4 ± 0.7 years, height of 169 + 2 cm, body mass of 63.1 ± 2.9 kg and VO ₂ max of 51.1 ± 1.8 ml kg^?1 min^?1, performed two randomly assigned treadmill runs at 70% VO ₂ max to exhaustion. No fluid was ingested during one trial (NF‐trial), whereas a single water bolus of 3.0 ml kg^?1 body mass was ingested immediately pre‐exercise and serial feedings of 2.0 ml kg^?1 body mass were ingested every 15 min during exercise in a fluid replacement trial (FR‐trial). Run time for the NF‐trial was 77.7 ± 7.7 min, compared to 103 ± 12.4 min for the FR‐trial (P<0.01). Body mass (corrected for water ingestion) decreased by 2.0 ± 0.2% in the NF‐trial and 2.7 ± 0.2% in the FR‐trial (P<0.01), while plasma volume decreased by 1.1 ± 1.1% and 3.5 ± 1.1% in the two trials respectively (N.S.). However, these apparent differences in circulatory volume were not associated with differences in rectal temperature. Respiratory exchange ratios indicated increased carbohydrate metabolism (73% vs 64% of total energy expenditure) and suppressed fat metabolism after 75 min of exercise in the NF‐trial compared with the FR‐trial (NF‐trial, 0.90 ± 0.01; FR‐trial, 0.86 ± 0.03; P<0.01). Blood glucose concentrations were similar in both trials, while blood lactate concentrations were higher in the NF‐trial at the end of exercise (4.83 ± 0.34 vs 4.18 ± 0.38 mM; P<0.05). In summary, water ingestion during prolonged running improved endurance capacity.