International journal of sport nutrition最新文献

The effects of preexercise feeding on responses to endurance exercise and performance were investigated. Untrained adolescent boys (N = 13, age 14.9 +/- 0.5 years) completed three endurance test sessions separated by a minimum of 72 hr. Each session consisted of 75 min of cycling at 60% of VO2 max followed by a high-intensity performance test. Dietary conditions were a candy bar (C1: 280 kcal, 36 g CHO), fat-free fig bars (C2: 200 kcal, 44 g CHO), and a nonnutritive sweetened drink (C3: placebo), ingested 10 min prior to exercise. Respiratory gases, heart rate, blood glucose, and lactate concentrations were measured throughout the test. ANOVA results revealed significant time effects for all variables; however, no differences were seen among the conditions. Performance times, 311.9 +/- 38.5 s in C1, 316.2 +/- 37.3 s in C2, and 328.1 +/- 46.4 s in C3, were not significantly different among conditions. Thus, preexercise feeding did not affect responses to endurance exercise or performance in adolescent boys.

Training (T) and prerace (PR) dietary intakes of male and female athletes participating in a 90-km ultramarathon and the usual diets of matched, sedentary controls were investigated using 24-hr dietary records. Supplement use, mean weekly training distance, and race performance times were recorded. Macro- and micronutrient intakes were analyzed using computerized nutritional analysis programs. Total mean energy intake in the T and PR diets of the runners was 10.1 and 12.8 MJ in the men (n = 150) and 7.5 and 9.1 MJ in the women (n = 23). Mean relative contribution of CHO to the runners' total kilojoule intake increased from 50.0 and 49.5% in the T diets to 57.7 (p < .05; n = 153) and 56.4% (p < .05; n = 23) in the PR diets of male and female runners, respectively, and energy-boosting supplements were included in the PR diets of 48% of female and 59% of male runners. Seventy-eight percent of female and 62% of male runners used vitamin and mineral supplements in their T diets as opposed to 39% of female and 28% of male controls. No statistically significant relationship was found between total kilojoule, CHO, fat, protein, and selected micronutrient intake during the 3 days before the race and performance in the 90-km event in runners of homogenous training status and gender.

This study investigated the hypothesis that addition of Na+ to a rehydration beverage would stimulate drinking and augment restoration of body water in individuals dehydrated during 90 min of continuous treadmill exercise in the heat. Following a 3.0 +/- 0.2% decrease in body weight (BW), 6 subjects sat in a thermoneutral environment for 30 min to allow body fluid compartments to stabilize. Over the next 3 hr, subjects rehydrated ad libitum using either flavored/artificially sweetened water (H2O-R) or a flavored, 6% sucrose drink containing either 25 (LNa(+)-R) or 50 (HNa(+)-R) mmol/L NaCl. Results demonstrated that rapid removal of the osmotic stimulus, during H2O-R, and the volume-dependent dipsogenic stimuli, during HNa(+)-R, are important factors in limiting fluid intake during rehydration, compared to LNa(+)-R. It was also found that the pattern of fluid replacement and restoration of fluid balance following dehydration is influenced by the dehydration protocol used to induce the loss in total body water and the sodium content of the rehydration beverage.

This investigation was undertaken to determine whether consuming several small feedings of preexercise carbohydrate (CHO), rather than a single bolus, would affect blood glucose and insulin responses during rest and exercise. Eight trained cyclists ingested 22.5, 45, or 75 total g maltodextrin and dextrose dissolved in 473 ml of water or an equal volume of placebo (PL). Drinks were divided into four portions and consumed at 15-min intervals in the hour before a 120-min ride at 66% VO2max. Serum glucose values were elevated by the CHO feedings at rest and fell significantly below baseline and PL at 15 min of exercise. However, glucose concentrations were similar in each of the CHO trials. Insulin concentrations also increased rapidly during rest, then fell sharply at the onset of exercise. The findings demonstrate that CHO consumed within an hour before exercise, even when taken in several small feedings, can produce transient hypoglycemia near the onset of exercise. Additionally, the magnitude of the response appears to be unrelated to either the amount of CHO ingested or the insulin response.

The purpose of this study was to compare the gastric emptying rates (GER) of water, a 6% carbohydrate (CHO) beverage, and a 20% CHO beverage and to contrast those rates against the rate at which deuterium oxide in the drinks accumulated in plasma (DAR) following beverage ingestion. Ten subjects (8 males, 2 females) cycled at 60% VO2max for 70 min; at 13 min, the subjects ingested 400 ml of one of the beverages. The GER and DAR of water and 6% CHO were similar, while GER and DAR were both significantly slowed by ingestion of 20% CHO. Although there was a significant correlation (r = .63, p < .05) between GER and DAR, only 40% of the variation in DAR could be accounted for by variation in GER. These data support the contention that DAR is partially determined by GER, with differences in the rate of fluid absorption across the intestine and other factors accounting for the remaining variation in DAR.

The oxidation of 13C-labeled glucose and fructose ingested as a preexercise meal between 180 and 90 min before exercise was measured on 6 subjects when either a placebo or sucrose was ingested during the exercise period. Labeled hexose oxidation, which occurred mainly during the first hour of exercise, was not significantly modified when sucrose was ingested, but exogenous glucose oxidation was significantly higher than exogenous fructose oxidation in both situations. The results suggest that the absorption rate of exogenous hexoses was high when exercise was initiated but diminished thereafter, and that glucose and fructose released from sucrose ingested during exercise did not compete with glucose or fructose ingested before exercise for intestinal absorption, for conversion into glucose in the liver (for fructose), or for uptake and oxidation of glucose in peripheral tissues. However, as already shown, in terms of availability for oxidation of carbohydrates provided by the preexercise meal, glucose should be favored over fructose.

The purpose of this study was to investigate the effect of oral allithiamine administration on isokinetic parameters of muscle performance and lactate accumulation prior to, during and in recovery from isokinetic exercise. A double-blind, counterbalanced, crossover experimental design utilizing a Biodex System 2 Isokinetic Dynamometer was used to test 15 healthy college students. Subjects orally ingested either 1 g. day-1 of a thiamin derivative, allithiamine, or placebo for 5 days and then performed six exercise sets of knee extension and flexion. ANOVA revealed no significant differences between treatment conditions in peak torque, mean peak torque, average power, or total work performed (p > .05). Likewise, lactate accumulation was not significantly different between treatment conditions at any measurement point (p > .05). The absence of significant differences suggests that oral allithiamine administration does not enhance isokinetic parameters of muscle performance or lactate accumulation prior to, during, and following isokinetic exercise.