O’Brien WJ and DS Rowlands. Fructose-maltodextrin ratio in a carbohydrate-electrolyte solution differentially affects exogenous carbohydrate oxidation rate, gut comfort, and performance. Am J Physiol Gastrointest Liver Physiol 300: G181–G189, 2011. Abstract: Solutions containing multiple carbohydrates utilizing different intestinal transporters (glucose and fructose) show enhanced absorption, oxidation, and performance compared with single-carbohydrate solutions, but the impact of the ratio of these carbohydrates on outcomes is unknown. In a randomized double-blind crossover, 10 cyclists rode 150 min at 50% peak power, then performed an incremental test to exhaustion, while ingesting artificially sweetened water or one of three carbohydrate-salt solutions comprising fructose and maltodextrin in the respective following concentrations: 4.5 and 9% (0.5-Ratio), 6 and 7.5% (0.8-Ratio), and 7.5 and 6% (1.25-Ratio). The carbohydrates were ingested at 1.8 g/min and naturally 13C-enriched to permit evaluation of oxidation rate by mass spectrometry and indirect calorimetry. Mean exogenous carbohydrate oxidation rates were 1.04, 1.14, and 1.05 g/min (coefficient of variation 20%) in 0.5-, 0.8-, and 1.25-Ratios, respectively, representing likely small increases in 0.8-Ratio of 11% (90% confidence limits; 4%) and 10% (4%) relative to 0.5- and 1.25-Ratios, respectively. Comparisons of fat and total and endogenous carbohydrate oxidation rates between solutions were unclear. Relative to 0.5-Ratio, there were moderate improvements to peak power with 0.8- (3.6%; 99% confidence limits 3.5%) and 1.25-Ratio (3.0%; 3.7%) but unclear with water (0.4%; 4.4%). Increases in stomach fullness, abdominal cramping, and nausea were lowest with the 0.8- followed by the 1.25-Ratio solution. At high carbohydrate-ingestion rate, greater benefits to endurance performance may result from ingestion of 0.8- to 1.25-Ratio fructose maltodextrin solutions. Small perceptible improvements in gut comfort favor the 0.8-Ratio and provide a clearer suggestion of mechanism than the relationship with exogenous carbohydrate oxidation

Jeukendrup AE. Carbohydrate feeding during exercise. European Journal of Sport Science 8:2, 77-86, 2008. Abstract: Carbohydrate ingestion can improve endurance capacity and performance. Since the 1980s, research has focused on optimizing the delivery strategies of these carbohydrates. The optimal dose of carbohydrate is still subject to debate, but recent evidence suggests that there may be a dose response effect as long as the carbohydrate ingested is also oxidized and does not result in gastrointestinal distress. Oxidation rates of a single type of carbohydrate do not exceed 60 g/h. However, when multiple transportable carbohydrates are ingested (i.e. glucose and fructose), these oxidation rates can be increased significantly (up to 105 g/h). To achieve these high oxidation rates, carbohydrate needs to be ingested at high rates and this has often been associated with poor fluid delivery as well as gastrointestinal distress. However, it has been suggested that using multiple transportable carbohydrates may enhance fluid delivery compared with a single carbohydrate and may cause relatively little gastrointestinal distress. More research is needed to investigate the practical applications of some of the recent findings discussed in this review

Maughan, RJ. Fluid and electrolyte loss and replacement in exercise. J Sports Sci. 1991 Summer; 9 Spec No: 117-42. Abstract: Prolonged exercise leads to a progressive water and electrolyte loss from the body as sweat is secreted to promote heat loss. The rate of sweating depends on many factors and is increased in proportion to the work rate and the environmental temperature and humidity. Sweat rate is highly variable between individuals, and can exceed 21 h-1 for prolonged periods. Since it is established that dehydration will impair exercise capacity and can pose a risk to health, the intake of fluid during exercise to offset sweat loss is important. Fluid intake is also aimed at providing a source of substrate, usually in the form of carbohydrate. The availability of ingested fluids may be limited by gastric emptying or by intestinal absorption. Gastric emptying of liquids is slowed by the addition of carbohydrate in proportion to the carbohydrate concentration and osmolality of the solution. With increasing glucose concentration, the rate of fluid delivery to the small intestine is decreased, but the rate of glucose delivery is increased. Water absorption in the small intestine is a passive process and is stimulated by the active absorption of glucose and sodium. The optimum fluid for rehydration during exercise depends on many factors, particularly the intensity and duration of the exercise, the environmental conditions, and the individual physiology of the athlete. There is no advantage to fluid intake during exercise of less than 30 min duration. The composition of fluids to be used will depend on the relative needs to replace water and to provide substrate. Where rehydration is a priority the solution should contain some glucose and sodium and should not exceed isotonicity: this will require the glucose concentration to be low (20-309 g l-1) or the substitution of glucose polymers, and the sodium content to be high (perhaps as much as 60 mmol l-1). Where substrate provision is more important, a more concentrated solution, incorporating large amounts of glucose polymers in concentrations of 150-200 g l-1, is to be preferred. To minimize the limitation imposed by the rate of gastric emptying, the volume of fluid in the stomach should be kept as high as is comfortable by frequent ingestion of small amounts of fluid. Addition of sodium, and perhaps also of potassium, may be important for rehydration after exercise.

Nielsen FH and HC Lukaski. Update on the relationship between magnesium and exercise. Magnes Res. 2006 Sep; 19 (3): 180-9. Abstract: Magnesium is involved in numerous processes that affect muscle function including oxygen uptake, energy production and electrolyte balance. Thus, the relationship between magnesium status and exercise has received significant research attention. This research has shown that exercise induces a redistribution of magnesium in the body to accommodate metabolic needs. There is evidence that marginal magnesium deficiency impairs exercise performance and amplifies the negative consequences of strenuous exercise (e.g., oxidative stress). Strenuous exercise apparently increases urinary and sweat losses that may increase magnesium requirements by 10-20%. Based on dietary surveys and recent human experiments, a magnesium intake less than 260 mg/day for male and 220 mg/day for female athletes may result in a magnesium-deficient status. Recent surveys also indicate that a significant number of individuals routinely have magnesium intakes that may result in a deficient status. Athletes participating in sports requiring weight control (e.g., wrestling, gymnastics) are apparently especially vulnerable to an inadequate magnesium status. Magnesium supplementation or increased dietary intake of magnesium will have beneficial effects on exercise performance in magnesium-deficient individuals. Magnesium supplementation of physically active individuals with adequate magnesium status has not been shown to enhance physical performance. An activity-linked RNI or RDA based on long-term balance data from well-controlled human experiments should be determined so that physically active individuals can ascertain whether they have a magnesium intake that may affect their performance or enhance their risk to adverse health consequences (e.g., immunosuppression, oxidative damage, arrhythmias)

Imagawa TF, I Hirano, K Utsuki, M Horie, A Naka, K Matsumoto and S Imagawa. Caffeine and taurine enhance endurance performance. Int J Sports Med. 2009 Jul; 30 (7): 4858. Abstract: Caffeine enhances endurance performance; however, its effect on accumulated lactate remains unclear. Conversely, taurine, which also enhances endurance performance, decreases accumulated lactate. In this study, the effect of combination of caffeine and taurine on endurance performance was assessed. Mice ran on a treadmill, and the accumulated lactate was measured. In addition, muscle fibers from the gastrocnemius muscle of the mice were stained with ATPase and analyzed. The use of caffeine and taurine over a 2 week period enhanced endurance performance. Moreover, taurine significantly decreased the accumulated concentration of lactate over long running distances. However, the diameter of the crosssections and ratios of Types I, IIA, and IIB muscle fibers were not affected