Fate of ingested fluids: factors affecting gastric emptying and intestinal absorption of beverages in humans.

The volume of fluid ingested for rehydration is essential in determining the restoration of euhydration because it must be in excess of the water lost since the individual was last euhydrated. The formulation of any ingested beverage is also important as this affects the rate at which the fluid is emptied from the stomach, absorbed in the small intestine, and hence assimilated into the body water pool. This review highlights the essential role of the gastrointestinal tract in the maintenance of hydration status.

The effects of Ramadan intermittent fasting on athletic performance: recommendations for the maintenance of physical fitness.

The behavioural modifications that accompany Ramadan intermittent fasting (RIF) are usually associated with some alterations in the metabolic, physiological, and psychological responses of athletes that may affect sport performance. Muslim athletes who are required to train and/or compete during the month-long, diurnal fast must adopt coping strategies that allow them to maintain physical fitness and motivation if they are to perform at the highest level. This updated review aims to present the current state of knowledge of the effects of RIF on training and performance, focusing on key-factors that contribute to the effects of Ramadan on exercise performance: energy restriction, sleep deprivation, circadian rhythm perturbation, dehydration, and alterations in the training load. The available literature contain few studies that have examined the effects of RIF on physical performance in athletes and, to date, the results are inconclusive, so the effects of RIF on competition outcomes are not at present wholly understood. The diverse findings probably indicate individual differences in the adaptability and self-generated coping strategies of athletes during fasting and training. However, the results of the small number of well-controlled studies that have examined the effects of Ramadan on athletic performance suggest that few aspects of physical fitness are negatively affected, and where decrements are observed these are usually modest. Subjective feelings of fatigue and other mood indicators are often cited as implying additional stress on the athlete throughout Ramadan, but most studies show that these factors may not result in decreases in performance and that perceived exercise intensity is unlikely to increase to any significant degree. Current evidence from good, well-controlled research supports the conclusion that athletes who maintain their total energy and macronutrient intake, training load, body composition, and sleep length and quality are unlikely to suffer any substantial decrements in performance during Ramadan. Further research is required to determine the effect of RIF on the most challenging events or exercise protocols and on elite athletes competing in extreme environments.

Effects of Ramadan intermittent fasting on sports performance and training: a review.

The month-long diurnal Ramadan fast imposes a major challenge to Islamic athletes. Sporting events are programmed throughout the year, with the result that training and competition are often scheduled during Ramadan. The small numbers of well-controlled studies that have examined the effects of Ramadan on athletic performance suggest that few aspects of physical fitness are negatively affected, and only modest decrements are observed. Whereas subjective feelings of fatigue and other mood indicators are often cited as implying additional stress on the athlete throughout Ramadan, most studies show these measures may not be reflected in decreases in performance. The development and early implementation of sensible eating and sleeping strategies can greatly alleviate the disruptions to training and competitiveness, thus allowing the athlete to perform at a high level while undertaking the religious intermittent fast. Nevertheless, further research is required to understand the mechanisms and energy pathways that allow athletes to maintain their performance capacities during Ramadan, and which factors are responsible for the observed decrements in performance of some individuals.

The F-MARC study on Ramadan and football: research design, population, and environmental conditions.

Ramadan is a month of penance during which Muslims take food or drink only after sunset and before the sun rises. This fast can present a considerable challenge to the Muslim athlete. Sports performance in those who observe Ramadan and those who do not has not been formally compared. Four Tunisian junior football squads participated in the study, and it was the individual's choice whether they observed the Ramadan fast. In this study, 64 players fasted while 36 players did not. Players completed daily questionnaires on perception of training difficulty before and during Ramadan. Anthropometric data were recorded 3 weeks before Ramadan, during the second and fourth weeks of Ramadan, and into the third week after Ramadan. Performance tests (sprint, leg power, agility, aerobic endurance, football-specific skills) were also measured on these test days. Nutritional intake was recorded by recall three times during each phase of the study. Haematological and biochemical analyses were performed on a 7-ml blood sample taken from each participant on each of the test days. Sweat samples were collected during a training session in the third week of Ramadan, when heart rate was also measured. The data analyses are presented and discussed elsewhere in this issue.

Influence of Ramadan fasting on physiological and performance variables in football players: summary of the F-MARC 2006 Ramadan fasting study.

The timing of food and liquid intake depends on the times of sunset and sunrise during the month of Ramadan. The current body of knowledge presents contradicting results as to the effect of Ramadan fasting on body mass, body composition and metabolic changes. The main objective of the present investigation was to gain additional information and scientific data in conformity with the philosophical background of Islam to allow optimisation of the daily training and dietary regimen in relation to the mental and physical performance of football players. The four teams, along with their coaches and trainers, attended a residential training camp at training centre 3 weeks before the start of Ramadan and throughout the study. Energy intake was relatively stable in the fasting group, but there was a small, albeit significant, decrease of approximately 0.7 kg in body mass. Water intake increased on average by 1.3 l/day in line with the greater energy intake in the non-fasting group in Ramadan. Daily sodium intake fell during Ramadan in the fasting players but increased slightly in the non-fasting group. Fasting players trained on average 11 h after their last food and drink, and reported that they felt slightly less ready to train during the Ramadan fast. None of the assessed performance variables was negatively affected by fasting while nearly all variables showed significant improvement at the third test session, indicating a training effect. Heart rate measurements in one training session during the third week of Ramadan appeared to suggest that the training load during training was marginally greater for the fasting than for the non-fasting players. However, the overall exercise load measures indicated that there was no biologically significant difference between the fasting and non-fasting groups. In the present study, biochemical, nutritional, subjective well-being and performance variables were not adversely affected in young male football players who followed Ramadan fasting in a controlled training camp environment. Physical performance generally improved, but match performance was not measured. We recommend that players should ensure adequate sleep and good nutrition during Ramadan to preserve football performance and general health.

The influence of Ramadan on physical performance measures in young Muslim footballers.

Ramadan alters the normal patterns of food intake and sleep. The aim of this study was to describe the impact of Ramadan on physical performance in youth Muslim athletes. The members of four Tunisian teams (age 18 years, N = 85) resided at the Tunisian Football Federation training ground. Each player chose either to fast or not fast during the 4-week period of Ramadan. Two teams were randomly chosen for morning testing; the remaining teams were tested in the afternoon. Testing took place 3 weeks before and in the second and fourth weeks of Ramadan. A subgroup of 45 players was tested again 3 weeks after Ramadan. Each player was assessed for speed, power, agility, endurance, and for passing and dribbling skills. No variables were negatively affected by fasting. Almost all variables had improved significantly by the third test session (training effect). A limited number of variables were also significant for time of day or in an interaction with week of testing. Changes in performance were most likely due to the effects of training and familiarity with the test methods. Based on these data, Ramadan had little effect on objective tests of physical performance in this sample of youth players observing Ramadan.

Effect of Ramadan fasting on some biochemical and haematological parameters in Tunisian youth soccer players undertaking their usual training and competition schedule.

Competitive Muslim athletes often have to train and compete during the holy month of Ramadan when they abstain from food and drink from sunrise to sunset. In this study, we investigated the effect of Ramadan fasting on some biochemical and haematological parameters in 78 Tunisian junior male soccer players aged 16-19 years who continued their usual schedule of daily training and weekly competition. The study population was divided into four groups based on the time of day of sampling (am or pm) and on whether they were fasting (48 players: 28 am and 20 pm) or non-fasting (30 players: 14 am and 16 pm). Resting venous blood samples were collected approximately 3 weeks before Ramadan, after 2 and 4 weeks of Ramadan, and 3 weeks after the end of Ramadan. Some small, but statistically significant, modifications were observed in circulating concentrations of haemoglobin, ferritin, transferrin, creatinine and cortisol, but the mean values for all variables were always within the reference ranges. The minor changes observed during Ramadan may be explained by changes in patterns of food consumption, activity patterns and by hypohydration. The results suggest that the combination of the changes in eating time and frequency during Ramadan fasting, together with the continuation of normal training load, has no marked effect on the blood profiles of these adolescent athletes.

Alteration of subjective feelings in football players undertaking their usual training and match schedule during the Ramadan fast.

Eighty-seven players (54 fasting players, 33 non-fasting players) who carried out their club's scheduled training and competitive matches completed the daily questionnaire before and during Ramadan. Fasting players trained on average 11 h after their last food and drink. While fasting players reported that they were slightly less ready to train during the Ramadan fast than in the period before Ramadan, there was no increase in their perceived effort during training or in training difficulty compared with their ratings before Ramadan, or with those of the non-fasting group during Ramadan. The fasting players were marginally more thirsty, hungry and tired, and slightly less able to concentrate before training during Ramadan than in the pre-Ramadan period. Before Ramadan, both groups averaged more than 9 h sleep each night. The non-fasting players recorded that they had about 105 min less sleep per night during the first week of Ramadan, before reverting back to their pre-Ramadan amount of sleep. The fasting group consistently reported having about 1 h less sleep per night throughout Ramadan, but neither group appeared to find sleep quality to have altered. In the first 2 weeks after Ramadan, the modest changes reported by the fasting players reverted back to their pre-Ramadan values.

Intensity of a training session during Ramadan in fasting and non-fasting Tunisian youth football players.

Heart rate was measured in 79 young male soccer players during training in the third week of Ramadan. Forty-eight players were practising Ramadan fasting, while the other 31 players were eating normally. All participants trained for 60-80 min at an ambient temperature of 25-28 degrees C and relative humidity of 50-53%. Heart rate, which was measured throughout the training session, was marginally higher in the fasting (mean 144 beats . min(-1), s = 25) than in the non-fasting (139 beats . min(-1), s = 23) group (P < 0.001). When assessed as the percentage of heart rate reserve utilized, however, the training load was similar for both groups (62%, s = 8). No difference was detected in training intensity for the fasting and non-fasting groups when quantified by either training impulse (253, s = 139 and 253, s = 108, respectively) or training load indicator (222, s = 123 and 179, s = 49, respectively). The overall subjective rating of perceived exertion of the training session reported 20 min after finishing training was similar for the fasting (12, range 6-17) and non-fasting (12, range 7-17) groups, which was comparable (P = 0.16) to the mean value for the entire week (13, range 8-16). A similar finding was observed in the players' subjective appraisal of the difficulty of training of the individual session and for the whole week's training. Overall exercise load measures indicated that there was no biologically significant difference between the fasting and non-fasting groups during training in the third week of Ramadan.

Gastric emptying of fluids during variable-intensity running in the heat.

This study examined gastric emptying, core temperature, and sprint performance during prolonged intermittent shuttle running in 30 degrees C when ingesting a carbohydrate-electrolyte solution (CES) or flavored water (FW). Nine male soccer players performed 60 min of shuttle running, ingesting fluid before exercise and every 15 min during exercise. Gastric emptying was measured using a double-sampling aspiration technique, and intestinal temperature was monitored via ingested capsules. There were no differences between trials in the total fluid volume emptied from the stomach during each exercise period (P = 0.054). The volume emptied every 15 min was 244 +/- 67 mL in the CES trial and 273 +/- 66 mL in the FW trial. Intestinal temperature was higher during exercise in the CES trial (P = 0.004), and cumulative sprint time was shorter (P = 0.037). Sprint performance was enhanced by the ingestion of a CES, which resulted in elevated core temperatures, and the rate of gastric emptying remained similar between solutions.

Errors in the estimation of hydration status from changes in body mass.

Hydration status is not easily measured, but acute changes in hydration status are often estimated from body mass change. Changes in body mass are also often used as a proxy measure for sweat losses. There are, however, several sources of error that may give rise to misleading results, and our aim in this paper is to quantify these potential errors. Respiratory water losses can be substantial during hard work in dry environments. Mass loss also results from substrate oxidation, but this generates water of oxidation which is added to the body water pool, thus dissociating changes in body mass and hydration status: fat oxidation actually results in a net gain in body mass as the mass of carbon dioxide generated is less than the mass of oxygen consumed. Water stored with muscle glycogen is presumed to be made available as endogenous carbohydrate stores are oxidized. Fluid ingestion and sweat loss complicate the picture by altering body water distribution. Loss of hypotonic sweat results in increased osmolality of body fluids. Urine and faecal losses can be measured easily, but changes in the water content of the bladder and the gastrointestinal tract cannot. Body mass change is not always a reliable measure of changes in hydration status and substantial loss of mass may occur without an effective net negative fluid balance.

Serotonin2C receptor blockade and thermoregulation during exercise in the heat.

PURPOSE: The effect of serotonin (5-HT)2C receptor blockade on the thermal response and exercise performance during exercise in a warm environment was examined. METHODS: Seven endurance-trained, but not heat-acclimatized, individuals (six males and one female) performed two 40-km time trials on a static cycle ergometer in a climatic chamber maintained at a mean (SD) ambient temperature of 35.5 (0.4) degrees C. The 5-HT2C receptor antagonist, pizotifen (1.5 mg), or placebo was administered orally on the evening before and again 6 h before exercise began. RESULTS: Resting rectal temperature (Tre) was higher (P=0.03) after pizotifen than placebo administration. Tre increased over time during exercise in both trials and was higher (P<0.05) during exercise in the pizotifen trial compared with the placebo trial from 40 to 60 min of exercise. There was no difference in Tre on completion of the time trial. The median times (range) required to complete the 40-km trials were 75.4 (69.0-82.5) and 76.1 (68.0-82.1) min in the pizotifen and placebo trials, respectively. Despite a trend for speed to be slower in the later stages of exercise in the pizotifen trial, performance was not significantly influenced by administration of pizotifen (P=0.86). Resting serum prolactin (Prl) and cortisol concentrations were not different after pizotifen or placebo administration. In both trials, serum Prl and cortisol values increased over time and were increased relative to resting levels in both trials (P<0.01) but were not different between treatments. CONCLUSION: The present study suggests that 5-HT may influence body temperature via an effect on the 5-HT2C receptors, but this effect was not sufficient to influence performance.

The effect of intermittent high-intensity running on gastric emptying of fluids in man.

PURPOSE: This study examined the effect of variable-intensity shuttle running on gastric emptying of a carbohydrate-free placebo (Plac) drink and of a 6.4% carbohydrate-electrolyte (CHO) sports drink. METHOD: We compared the volume of test drink emptied during two 15-min periods of walking exercise (WE) with that during two 15-min periods of the Loughborough Intermittent Shuttle Test (LIST). Gastric emptying was measured on the four trials using a double-sampling aspiration technique in eight healthy males after ingestion of a 420 +/- 49 mL and a 168 +/- 20 mL bolus of the appropriate test drink at the start of the first and second exercise period, respectively. RESULTS: During the initial 15 min of exercise, the mean (+/-SD) volume of Plac (124 +/- 95 mL) and CHO (71 +/- 43 mL) drink emptied was similar between the two LIST trials, but the volume of Plac (227 +/- 85 mL) and CHO (159 +/- 63 mL) drinks emptied on the WE trials was greater than for the respective test drinks on the LIST trials. Similar volumes of test drinks were emptied on all trials (P = 0.20) during the second 15 min of exercise. Over the 30 min of each trial, the exercise intensity of the LIST reduced the volume of the Plac (211 +/- 108 mL) and CHO (208 +/- 83 mL) drink emptied compared with that on the WE trial for the Plac (396 +/- 74 mL) and CHO (293 +/- 73 mL) drink, respectively. CONCLUSIONS: The exercise intensity of the LIST is sufficient to slow gastric emptying of carbohydrate and noncarbohydrate containing drinks compared with walking. Dilute carbohydrate-electrolyte drinks empty at about the same rate as carbohydrate-free beverages during variable-intensity running.

Comparison of water turnover rates in young swimmers in training and age-matched non-training individuals.

Total body water (TBW) and water turnover rates (WTR) of 8 competitive swimmers (SW) and 6 age-matched non-training individuals (CON) were determined using deuterium oxide dilution and elimination. During the 7-day study, individuals in the SW group trained 9 times, swimming on average 42.4 km, while the CON group did no regular exercise. Water temperature in the swimming pool was between 26 and 29 degrees C during training sessions. Body mass at the beginning and end of the study period remained essentially the same in the SW (67.8+/- 6.3 kg) and CON (61.1 +/- 8.5 kg) groups. Mean +/- SD TBW of the SW (38.7+/- 5.6 L) was similar to that of the CON (37.5 +/- 8.0 L). Mean WTR was faster in the SW (54 +/- 18 ml x kg x day(- 1) than the CON (28+/- 21 ml x kg x day(-1)). Mean daily urine output was similar in the SW (14 +/- 5 ml x kg x day(-1)) and CON (14+/- 3 ml x kg x day(-1)). Calculated non-renal daily water loss was faster in the SW (41 +/- 21 ml x kg x day(-1)) than the CON (13 +/- 20 ml x kg x day(-1)). This study demonstrates that WTR are faster in young swimmers who exercise strenuously in cool water than in non-training individuals and that the difference was due to the approximately 3-times greater non-renal water losses that the exercising group incurred. This suggests that exercise-induced increases in sweat rates are a major factor in water loss in swimmers training in cool water.

Gastric emptying and fluid availability after ingestion of glucose and soy protein hydrolysate solutions in man.

The double sampling gastric aspiration method was used to measure the effect of energy content on the rate of gastric emptying of glucose and soy protein hydrolysate solutions. The net rate of absorption of water from these solutions was assessed using deuterium oxide as a tracer for water. Six healthy male subjects were each studied on four separate occasions using a test drink volume of 600 ml. The half emptying times (t 1/2, median (range)) of the iso-energetic soy protein hydrolysate (6P, 60 g l(-1), 36 (14-39) min) and glucose (7G, 70 g l(-1), 25 (19-29) min) solutions were similar. These two solutions (6P, 7G) delivered energy to the small intestine at similar rates, and resulted in similar rates of accumulation of the deuterium tracer in the circulation. The dilute glucose solution (LG, 23 g l(-1)) was emptied faster (t 1/2 13 (11-19) min) and resulted in a faster rate of tracer accumulation in the circulation than any of the other solutions, including the iso-osmotic soy protein solution (LG 311 +/- 5 mosmol kg(-1), 6P 321 +/- 24 mosmol kg(-1)). The concentrated soy protein hydrolysate solution (12P, 120 g l(-1)) emptied more slowly (t 1/2 80 (44-120) min) than the more dilute solutions. The rate of energy delivery to the small intestine from 12P was similar to that from 6P for the first 50 min after ingestion, and similar to that from 7G at all sample points. These results indicate that the iso-energetic solutions of glucose and soy protein hydrolysate used in this study are emptied from the stomach at similar rates and result in similar rates of fluid availability after ingestion.