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Purpose: To investigate the effect on gastric emptying of intermittent exercise at varying intensities such as occurs during a soccer match., Methods: We compared the emptying rate of a carbohydrate-electrolyte (CE) drink during two 15-min periods of a competitive 5-a-side indoor soccer match separated by 10 min and during two 15-min periods of low-intensity walking exercise. Seven healthy male subjects, all of whom regularly played soccer, completed the study. Exercise intensity on each trial was calculated from heart rate recordings. Subjects ingested 500 mL of the CE drink immediately before starting each exercise period. Before and after completing each 15-min exercise period, the gastric contents were aspirated and the volume recorded. Ambient room temperature ranged from 16-22 degrees C and humidity ranged from 57-72% on both trials., Results: Mean +/- SD heart rate was higher during the Soccer trial than during the Walking trial at all time points. Exercise intensity was calculated to be 54 +/- 23% and 63 +/- 20% VO2max, respectively, for the first and second periods of exercise on the Soccer trial and 13 +/- 9% and 12 +/- 11% VO2max, respectively, for the first and second periods of exercise on the Walking trial. During the first 15-min period of exercise, a greater (median (range)) volume of the CE drink was emptied from the stomach on the Walking trial (247 mL (102-361 mL)) than on the Soccer trial (84 mL (17-230 mL); P = 0.022). In the second exercise period, however, gastric emptying rates were not different (P = 0.16) between the Walking trial (247 mL (104-363 mL)) and Soccer trial (148 mL (17-293 mL))., Conclusion: As indicated by heart rate, the overall exercise intensity of an indoor soccer match appears to be moderate. The pattern of activity during a match is intermittent with periods of low level activity punctuated by short bursts of high-intensity sprinting. The present study demonstrates that the intensity of activity during this type of exercise is sufficient to slow gastric emptying.

Purpose: The effect on gastric emptying of brief intermittent high-intensity sprints and a moderate-intensity steady-state cycle exercise was studied., Methods: Eight healthy male subjects were each studied at rest (R), during steady-state exercise at a constant power output corresponding to 66% of their VO(2max) (C66), during intermittent high-intensity exercise at a power output averaging 66% of their VO(2max) (I66), and during intermittent high-intensity exercise at a power output averaging 75% of their VO(2max) (I75). Gastric emptying was measured using the double-sampling gastric aspiration technique. Subjects ingested 600 mL of a 6% carbohydrate-electrolyte solution immediately before exercise or seated rest., Results: The volume of test solution in the stomach was less at all time points on trial I66 than on trial I75 (P = 0.023). The rate of gastric emptying, expressed as the median (range) time (minutes) taken to empty half the test meal volume (t(1/2)), was not different on trials R (20 (7--30)) and C66 (21 (7--49)), and was faster than on trial I75 (62 (27--100); P = 0.003 and P = 0.005, respectively). Median t(1/2) was faster on trial R than on trial I66 (30 (15--74) min; P = 0.019), but no difference was detected between C66 and I66 or between I66 and I75. However, over the initial 30 min period after ingestion, the median (range) volume of test drink delivered to the duodenum was faster (P < 0.01) on trials R (387 (296--541) mL) and C66 (389 (165--584) mL) than on trials I66 (331 (191--494) mL) or I75 (249 (79-335) mL)., Conclusion: The data demonstrate that gastric emptying of liquids is slowed during brief intermittent high-intensity exercise compared with rest or steady-state moderate exercise.

Restoration of fluid balance after exercise-induced hypohydration avoids the detrimental effects of a body water deficit on subsequent exercise performance and physiological function. Key issues in restoring fluid balance are consumption of a volume of fluid greater than that lost in sweat and replacement of electrolyte losses, particularly sodium.

Methods: After a familiarization period, six well-trained males participated in a diet and exercise regimen lasting 9 d and comprising three cycling tests to exhaustion. A work rate was selected during the familiarization period that would result in fatigue after approximately 90-100 min at an ambient temperature of 10 degrees C (i.e., approximately 75% of VO2max). The first exercise test was a depletion trial and was preceded by a period during which the subjects' normal diet was consumed. A prescribed 70% carbohydrate (CHO) diet was then consumed for 3.5 d. After this diet, a second exercise test was performed; one of two isoenergetic experimental meals was consumed 4 h before this test (70% CHO meal, CHO trial; or 90% fat meal, fat trial). The second exercise test was followed by a further 3.5-d period on the high CHO diet. Four hours before the third test, subjects consumed the other meal. Heparin was administered intravenously 30 min (1000 U), 15 min (500 U), and 0 min (500 U) before exercise on the fat trial. Subjects were assigned to the two meals in randomized order., Results: Time to exhaustion increased from 118.2 (12.4) min on the CHO trial to 127.9 (12.1) min on the fat trial (P = 0.001). Although no difference in VO2, RER, HR or RPE was found between trials, there was an earlier reduction in RER and an earlier rise in RPE on the fat trial. No difference in total CHO oxidation was found between trials (383 +/- 70 g on the CHO trial and 362 +/- 59 g on the fat trial)., Conclusions: These results suggest that increasing fat availability immediately before exercise by acute fat feeding and heparin infusion can improve endurance exercise in a cool environment in well-trained individuals. This study was not intended to have immediate application to the sports performance field but rather to contribute to our understanding of the factors that may limit endurance performance. Heparin injection to elevate plasma fatty acid concentration would not represent sound medical practice.

Purpose: The purpose of the present study was to examine the responsiveness of serotonergic receptors in endurance trained and sedentary men., Methods: The serum prolactin and cortisol responses to the oral administration of 30 mg of the serotonin releaser and reuptake inhibitor d-fenfluramine were determined in eight male endurance-trained subjects and seven male sedentary controls., Results: A Friedman's repeated-measures test for both the endurance-trained (P = 0.006) and sedentary (P = 0.018) prolactin results demonstrated a change in the mean prolactin concentration over time, but no difference in prolactin response was observed between the subject groups (P = 0.81). In both subject groups, the serum cortisol concentration remained unchanged. However, the mean serum concentration of cortisol for the endurance-trained subjects at each time point tended to be lower than at the corresponding time point for the sedentary subject group and was significantly lower at 180 min (P = 0.04)., Conclusion: The present study suggests that, in contrast to an earlier report of down-regulation of 5-HT1A receptor function in endurance-trained subjects in response to a nonspecific challenge, postsynaptic 5-HT2 function as determined by the d-fenfluramine-evoked alteration in the plasma concentration of prolactin is not altered by endurance training.

Purpose: The purpose of this study was to determine a quick and easy method for assessment of day-to-day hydration status in athletes in the heat., Methods: Measurement of the osmolality of the first urine sample of the day collected after wakening but before breakfast established a standardized collection procedure to allow day-to-day comparisons of individuals., Results: Laboratory measurements established that a difference in osmolality is found when individuals are dehydrated by a moderate extent in comparison with an euhydrated situation: the osmolality of the first morning urine sample of control subjects (N = 11) averaged over 5 d was 675 (+/- 232) mosmol.kg-1 (mean +/- SD). For subjects who were hypohydrated by exercise followed by fluid restriction, morning urine osmolality was 924 (+/- 99) mosmol.kg-1 (P < 0.001, N = 11, averaged over 7 d). Field measurements from 29 athletes undertaking warm weather training indicated that the athletes could, with appropriate feedback, maintain a satisfactory hydration status. Athletes in weight category sports tended to record a higher morning urine osmolality, reflecting their attempts to dehydrate: recorded values were 627 (+/- 186) mosmol.kg-1 (nonweight category sports, N = 8), 775 (+/- 263) mosmol.kg-1 (boxers, N = 15) and 777 (+/- 254) mosmol.kg-1 (wrestlers, N = 6). Results obtained with a hand-held portable conductivity were compared with those from measured osmolality., Conclusions: The findings suggest that such an instrument could provide athletes with reliable information as to their hydration status from measurement of the first morning urine of the day and therefore provide a quick and easy method for achieving an approximation of hydration status from day-to-day.

Eight healthy males performed four rides to exhaustion at approximately 70% of their VO2max obtained in a neutral environment. Subjects cycled at ambient temperatures (Ta) of 3.6 +/- 0.3 (SD), 10.5 +/- 0.5, 20.6 +/- 0.2, and 30.5 +/- 0.2 degrees C with a relative humidity of 70 +/- 2% and an air velocity of approximately 0.7 m.s-1. Weighted mean skin temperature (Tsk), rectal temperature (Tre), and heart rate (HR) were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of hemoglobin, hematocrit, blood metabolites, and serum electrolytes and osmolality. Expired air was collected for calculation of VO2 and R which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Time to exhaustion was significantly influenced by Ta (P = 0.001): exercise duration was shortest at 30.5 degrees C (51.6 +/- 3.7 min) and longest at 10.5 degrees C (93.5 +/- 6.2 min). Significant effects of Ta were also observed on VE, VO2, R, estimated fuel oxidation, HR, Tre, Tsk, sweat rate, and RPE. This study demonstrates that there is a clear effect of temperature on exercise capacity which appears to follow an inverted U relationship.

The interaction between the volume and composition of fluids ingested was investigated in terms of rehydration effectiveness. Twelve male volunteers, dehydrated by 2.06 +/- 0.02% (mean +/- SE) of body mass by intermittent cycle exercise, consumed a different drink volume on four separate weeks; six subjects received drink L (23 mmol.l-1 Na+) in each trial and six were given drink H (61 mmol.l-1 Na+). Volumes consumed were equivalent to 50%, 100%, 150%, and 200% of body mass loss (trials A, B, C, and D, respectively). Blood and urine samples were obtained before exercise and for 7.5 h after exercise. Less urine was excreted following rehydration in trial A than in all other trials. Cumulative urine output (median ml) was less in trial B (493, range 181-731) than D (1361, range 1014-1984), which was not different from trial C (867, range 263-1191) in group L. In group H, the volume excreted in trial B (260, range 137-376) was less than trials C (602, range 350-994) and D (1001, range 714-1425), and the volume in trial C was less than in trial D. These results suggest that both sodium concentration and fluid volume consumed interact to affect the rehydration process. A drink volume greater than sweat loss during exercise must be ingested to restore fluid balance, but unless the sodium content of the beverage is sufficiently high this will merely result in an increased urinary output.

The purpose of this study was to compare the rate of gastric emptying of 20 g.l-1 (2G), 40 g.l-1 (4G), and 60 g.l-1 (6G) glucose solutions with that of water (W). On separate occasions in randomized order, a 600-ml test solution was instilled into the stomach of each of six healthy male volunteers. Gastric emptying was measured at 10-min intervals for 1 h by a double sampling gastric aspiration method that allowed the volume of test drink and of the gastric secretion present in the stomach to be measured at each time point. All solutions emptied rapidly and followed an exponential emptying pattern. The 20 g.l-1 glucose solution was emptied at the same rate as water. After the first 10 min of rapid emptying, 4G and 6G were emptied slower (P < 0.05) than water. 6G delivered more (P < 0.05) glucose to the small intestine than 4G, and 4G delivered more glucose than 2G. The results indicate that a 20 g.l-1 glucose solution has no effect on gastric emptying compared with water, but that after the first 10 min of rapid emptying, glucose solutions at a concentration of 40 g.l-1 or more delay gastric emptying.

Formulation of oral rehydration solutions (ORS) is reviewed in the context of methods for measuring absorption of water and component substrates, transport mechanisms of substrates and water, requirements of the athlete, and effects of exercise on absorption. The triple lumen tube intubation perfusion method is the optimal technique for obtaining absorption data from the human small intestine during rest and exercise. Factors that must be considered when interpreting absorption data obtained by this technique include the role of the mixing segment in altering composition of the infused solution, defining optimal segment length, effects of ORS osmolality, and absorption of "nonabsorbed" indicators. Absorption data are applicable only to the test segment and may lack relevance to ORS transport proximal and distal to the test segment. Absorption rate of an ORS measured by perfusion may not correlate with absorption rate following ingestion. Transport of water, electrolytes, carbohydrates, and other solutes including glutamine and amino acids is considered in relation to ORS formulation. Factors affecting absorption of an ORS including the unstirred layer, motility, intestinal blood flow, and maximal absorptive capacity of the alimentary tract are considered. Exercise per se at 30-70% VO2max for 60-90 min probably has minimal effects in limiting absorption of an ORS. Consideration relevant to supplying needs of the athlete during prolonged exercise in relation for ORS formulation are discussed.

There is now substantive evidence that the provision of exogenous carbohydrate at high rates (1-2 g. min-1) can enhance performance during prolonged exercise. This finding has revived research into the factors determining the rate of exogenous carbohydrate delivery during exercise. While the rate of muscle oxidation of exogenous carbohydrate could be determined by the rate of gastric emptying or of intestinal carbohydrate absorption or of muscle glucose uptake and oxidation, most physiologists seem to have assumed that gastric emptying is the factor that limits the rate of exogenous carbohydrate delivery during exercise. Furthermore, studies of gastric emptying have suggested that the carbohydrate content of the ingested solution is an important factor determining its rate of gastric emptying. However, the findings of recent studies employing a repeated drinking design suggest that the gastric volume and therefore the pattern of drinking during exercise will have a significant, possibly major, influence on the rate of both carbohydrate and water delivery from any solution. This review considers this evidence and its practical implications for athletes who wish to ingest carbohydrate during exercise and for exercise physiologists designing studies to optimize carbohydrate delivery to muscle during exercise. It is proposed that, if gastric volume is an important determinant of the rate of gastric emptying, a more standardized method for reporting the rates of gastric emptying of different solutions should be adopted.