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Biomedical subjects

R J Maughan

Publications and source records attributed to R J Maughan.

At least 55 records · Page 3Linked to original sources
PubMed1998

Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses.

Sodium and water loss during, and replacement after, exercise-induced volume depletion was investigated in six volunteers volume depleted by 1.89 +/- 0.17% (SD) of body mass by intermittent exercise in a warm, humid environment. Subjects exercised in a large, open plastic bag, allowing collection of all sweat secreted during exercise. For over 60 min beginning 40 min after the end of exercise, subjects ingested drinks containing 0, 25, 50, or 100 mmol/l sodium (trials 0, 25, 50, and 100) in a volume (ml) equivalent to 150% of the mass lost (g) by volume depletion. Body mass loss and sweat electrolyte (Na+, K+, and Cl-) loss were the same on each trial. The measured sweat sodium concentration was 49.2 +/- 18.5 mmol/l, and the total loss (63.9 +/- 38.7 mmol) was greater than that ingested on trials 0 and 25. Urine production over the 6-h recovery period was inversely related to the amount of sodium ingested. Subjects were in whole body negative sodium balance on trials 0 (-104 +/- 48 mmol) and 25 (-65 +/- 30 mmol) and essentially in balance on trial 50 (-13 +/- 29 mmol) but were in positive sodium balance on trial 100 (75 +/- 40 mmol). Only on trial 100 were subjects in positive fluid balance at the end of the study. There was a large urinary loss of potassium over the recovery period on trial 100, despite a negligible intake during volume repletion. These results confirm the importance of replacement of sodium as well as water for volume repletion after sweat loss. The sodium intake on trial 100 was appropriate for acute fluid balance restoration, but its consequences for potassium levels must be considered to be undesirable in terms of whole body electrolyte homeostasis for anything other than the short term.

Adult↗
PubMed1997

Blood and urine acid-base status of premenopausal omnivorous and vegetarian women.

The effect of long-term differences in diet composition on whole-body acid-base status was examined in thirty-three young healthy females. The volunteers were recruited from two separate groups matched approximately for age, height and weight; one group regularly ate meat (omnivores; n 20) and one group did not (vegetarians; n 13). All subjects completed a 7 d weighed intake of food, and from their dietary records, total energy, carbohydrate (CHO), fat and protein content were estimated using computer-based food composition tables. During this week they reported to the laboratory on two occasions, following an overnight fast and separated by at least 48 h. Arterialized venous blood samples were obtained on each visit and these were analysed for blood acid-base status. Haemoglobin and packed cell volume, serum total cholesterol and HDL-cholesterol, serum albumin and total protein were also determined. Two 24 h urine collections were completed; the volume was recorded and samples were analysed for pH, titratable acid and Mg and Ca concentration. Total energy intake of the omnivores was greater (P = 0.0003) than that of the vegetarian group. Dietary intake of CHO (P = 0.024), fat (P = 0.0054) and protein (P = 0.0002) were higher in the omnivorous group than in the vegetarians. There were no differences between the two groups with respect to blood CO2 partial pressure, plasma HCO3- and blood base excess, but blood pH was slightly higher in the omnivores (P = 0.064). Measures of urine acid-base status suggested a lower pH in the omnivore group, but this difference was not statistically significant; a greater titratable acid output was observed with the omnivorous group compared with the vegetarians (48.9 (SE 20.3) v. 35.3 (SE 23.3) mEq/24h; P = 0.018). Although the dietary intake of Ca was not different between the two groups, urinary Ca excretion of the omnivores was significantly higher (3.87 (SD 1.34) v. 3.22 (SD 1.20) mmol/24 h) than that of the vegetarians (P = 0.014). It is suggested that the higher protein intake of the omnivores resulted in an increase in urinary total acid excretion, which may explain the higher rate of Ca excretion.

Acid-Base Equilibrium↗
PubMed1997

Diet composition and the performance of high-intensity exercise.

The crucial role of muscle glycogen as a fuel during prolonged exercise is well established, and the effects of acute changes in dietary carbohydrate intake on muscle glycogen content and on endurance capacity are equally well known. More recently, it has been recognized that diet can also affect the performance of high-intensity exercise of short (2-7 min) duration. If the muscle glycogen content is lowered by prolonged (1-1.5 h) exhausting cycle exercise, and is subsequently kept low for 3-4 days by consumption of a diet deficient in carbohydrate (< 5% of total energy intake), there is a dramatic (approximately 10-30%) reduction in exercise capacity during cycling sustainable for about 5 min. The same effect is observed if exercise is preceded by 3-4 days on a carbohydrate-restricted diet or by a 24 h total fast without prior depletion of the muscle glycogen. Consumption of a diet high in carbohydrate (70% of total energy intake from carbohydrate) for 3-4 days before exercise improves exercise capacity during high-intensity exercise, although this effect is less consistent. The blood lactate concentration is always lower at the point of fatigue after a diet low in carbohydrate and higher after a diet high in carbohydrate than after a normal diet. Even when the duration of the exercise task is kept constant, the blood lactate concentration is higher after exercise on a diet high in carbohydrate than on a diet low in carbohydrate. Consumption of a low-carbohydrate isoenergetic diet is achieved by an increased intake of protein and fat. A high-protein diet, particularly when combined with a low carbohydrate intake, results in metabolic acidosis, which ensues within 24 h and persists for at least 4 days. This appears to be the result of an increase in the circulating concentrations of strong organic acids, particularly free fatty acids and 3-hydroxybutyrate, together with an increase in the total plasma protein concentration. This acidosis, rather than any decrease in the muscle glycogen content, may be responsible for the reduced exercise capacity in high-intensity exercise; this may be due to a reduced rate of efflux of lactate and hydrogen ions from the working muscles. Alternatively, the accumulation of acetyl groups in the carbohydrate-deprived state may reduce substrate flux through the pyruvate dehydrogenase complex, thus reducing aerobic energy supply and accelerating the onset of fatigue.

Acidosis, Lactic↗
PubMed1997

Recovery from prolonged exercise: restoration of water and electrolyte balance.

Rapid and complete restoration of fluid balance after exercise is an important part of the recovery process, especially in hot, humid conditions, when sweat losses may be high. Rehydration after exercise can only be achieved if the electrolytes lost in sweat, as well as the lost water, are replaced. However, the amount of electrolytes lost in sweat is highly variable between individuals and although the optimum drink may be achieved by matching drink electrolyte intake with sweat electrolyte loss, this is virtually impossible in sport settings. The composition of sweat varies considerably not only between individuals, but also with time during exercise and it is further influenced by the state of acclimatization. A moderate excess of salt intake would appear to be beneficial as far as hydration status is concerned, without any detrimental effects on health, provided that fluid intake is in excess of sweat loss and the renal function is not impaired. To achieve effective rehydration following exercise in the heat, the rehydration beverage should contain moderately high levels of sodium (at least 50 mmol l-1), and possibly also some potassium. The addition of substrate is not necessary for rehydration, although a small amount of carbohydrate (< 2%) may improve the rate of intestinal uptake of sodium and water. The volume of beverage consumed should be greater than the volume of sweat lost to provide for the ongoing obligatory urine losses. Therefore, the palatability of the beverage is important. Many individuals may lose substantial amounts of sweat and will therefore have to consume large amounts of replacement fluids and this is more likely to be achieved if the taste is perceived as being pleasant. Water alone is adequate for rehydration purposes when solid food is consumed, as this replaces the electrolytes lost in sweat. However, there are many situations where intake of solid food is not possible or is deliberately avoided and, in these instances, the inclusion of electrolytes in rehydration beverages is essential. Where a second exercise bout has to be performed, replacement of sweat losses is an essential part of the recovery process. Exercise performance will be impaired if complete rehydration is not achieved.

Dietary Carbohydrates↗
PubMed1997

Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man.

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.

Adult↗
PubMed1997

The effect of sodium citrate ingestion on the metabolic response to intense exercise following diet manipulation in man.

Feeding a high-carbohydrate (CHO) diet and administration of alkalinizing agents have both been shown to improve performance in high-intensity exercise. The effect of these treatments in combination was investigated in the present study. Six healthy male subjects exercised to exhaustion on an electrically braked cycle ergometer at a power output equivalent to 100% of their maximum oxygen uptake (VO2,max) on four separate occasions. Each subject consumed either a diet with the same composition as his normal diet (termed the experimental normal (N) diet; 54 +/- 7% CHO, 13 +/- 2% protein, 33 +/- 7% fat) or a high-CHO diet (81 +/- 2% CHO, 13 +/- 2% protein, 6 +/- 1% fat) that had the same energy and protein content for the 3 days prior to the exercise tests. Subjects then ingested either a placebo (CaCO3) or trisodium citrate (0.3 g (kg body mass)-1) 3 h before exercise. Time to fatigue was not different between experimental conditions. Consumption of the high-CHO diet had no effect on blood acid-base status, but the ingestion of sodium citrate induced a mild metabolic alkalosis after both the N diet and the high-CHO diet. This alkalinizing effect was also evident after exercise, since blood pH, plasma bicarbonate and blood base excess were higher (P < 0.05) after the ingestion of sodium citrate than under the placebo conditions. The changes in blood lactate, pyruvate and glucose and plasma glycerol after exercise were similar for all experimental conditions. Blood lactate, glucose and pyruvate and plasma glycerol concentrations increased from resting values (P < 0.01) following exercise but this increase was similar under all experimental conditions. These data demonstrate that when the energy and protein content of the diets is the same, exercise capacity and the metabolic response to intense exercise are similar following consumption either of a high-CHO diet or a more normal diet. Acute ingestion of sodium citrate prior to exercise resulted in a reduction in post-exercise acidosis despite a blood lactate concentration that was similar to that observed after the ingestion of a placebo, but did not affect exercise performance under the conditions of this study.

Acid-Base Equilibrium↗
PubMed1997

Energy and macronutrient intakes of professional football (soccer) players.

OBJECTIVE: To examine the dietary habits of professional soccer players at two Scottish Premier League clubs during the competitive season. METHODS: A study of the dietary intake of 51 professional soccer players with two different clubs was carried out by the seven day weighed intake method. RESULTS: Physical characteristics of the two groups of players were similar, with only small differences in age and body mass but no difference in height and body fat. Mean (SD) daily energy intake for club A was 11.0 (2.6) MJ, and for club B 12.8 (2.2) MJ. The higher energy intake at club B was largely accounted for by a higher (P < 0.005) fat intake (118 v 93 g d-1): there was no difference in the absolute amounts of protein, carbohydrate, or alcohol consumed. When expressed as a fraction of total energy intake, mean protein intake was higher (P < 0.05) and fat intake lower (P < 0.01) at club A. CONCLUSIONS: The mean energy intake of these players was not high compared with athletes in endurance sports. Fractional contribution of the macronutrients to total energy intake was broadly similar to that of the general population.

Adolescent↗
PubMed1997

Factors influencing the restoration of fluid and electrolyte balance after exercise in the heat.

Maintenance of fluid balance is a major concern for all athletes competing in events held in hot climates. This paper reviews recent work relating to optimisation of fluid replacement after sweat loss induced by exercising in the heat. Data are taken from studies undertaken in our laboratory. Issues investigated were drink composition, volume consumed, effects of consuming food with a drink, effects of alcohol in rehydration effectiveness, voluntary intake of fluid, and considerations for women related to the menstrual cycle. The results are presented as a series of summaries of experiments, followed by a discussion of the implications. The focus of this review is urine output after ingestion of a drink; fluid excreted in urine counteracts rehydration. Also included are data on the restoration of plasma volume losses. Ingestion of large volumes of plain water will inhibit thirst and will also promote a diuretic response. If effective rehydration is to be maintained for some hours after fluid ingestion, drinks should contain moderately high levels of sodium (perhaps as much as 50-60 mmol/l) and possibly also some potassium to replace losses in the sweat. To surmount ongoing obligatory urine losses, the volume consumed should be greater than the volume of sweat lost. Palatability of drinks is important in stimulating intake and ensuring adequate volume replacement. Where opportunities allow, the electrolytes required may be ingested as solid food consumed with a drink. There are no special concerns for women related to changes in hormone levels associated with the menstrual cycle. Ingestion of carbohydrate-electrolyte drinks in the post-exercise period restores exercise capacity more effectively than plain water. The effects on performance of an uncorrected fluid deficit should persuade all athletes to attempt to remain fully hydrated at all times, and the aim should be to start each bout of exercise in a fluid replete state. This will only be achieved if a volume of fluid in excess of the sweat loss is ingested together with sufficient electrolytes.

Alcohol Drinking↗
PubMed1997

Whole body sweat collection in humans: an improved method with preliminary data on electrolyte content.

Previous methods used to collect human sweat for electrolyte analysis have been criticized because they involve only regional sampling or because of methodological problems associated with whole body-washdown techniques. An improved method for collection of whole body sweat from exercising subjects is described. It involved construction of a plastic frame that supports a large plastic bag within which the subject exercises. The subject and the equipment are washed with distilled, deionized water before exercise begins. After exercise is completed, the subject and equipment are again washed with water containing a marker not present in sweat (ammonium sulfate). Total sweat loss is calculated from the change in body mass, and the volume of sweat not evaporated is calculated from dilution of the added marker. Recovery of added water was 102 +/- 2% (SD) of the added volume, and recovery of added electrolytes was 99 +/- 2% for sodium, 98 +/- 9% for potassium, and 101 +/- 4% for chloride. Repeated trials (n = 4) on five subjects to establish the reproducibility of the method gave a coefficient of variation of 17 +/- 5% for sodium, 23 +/- 6% for potassium, and 15 +/- 6% for chloride. These values include the biological variability between trials as well as the error within the method. The biological variability thus appears to be far greater than the methodological error. Normal values for the composition of sweat induced by exercise in a hot, humid environment in healthy young men and women were (in mM) 50.8 +/- 16.5 sodium, 4.8 +/- 1.6 potassium, 1.3 +/- 0.9 calcium, 0.5 +/- 0.5 magnesium, and 46.6 +/- 13.1 chloride.

Adult↗
PubMed1997

Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption.

The effect of alcohol consumption on the restoration of fluid and electrolyte balance after exercise-induced dehydration [2.01 +/- 0.10% (SD) of body mass] was investigated. Drinks containing 0, 1, 2, and 4% alcohol were consumed over 60 min beginning 30 min after the end of exercise; a different beverage was consumed in each of four trials. The volume consumed (2,212 +/- 153 ml) was equivalent to 150% of body mass loss. Peak urine flow rate occurred later (P = 0.024) with the 4% beverage. The total volume of urine produced over the 6 h after rehydration, although not different between trials (P = 0.307), tended to increase as the quantity of alcohol ingested increased. The increase in blood (P = 0.013) and plasma (P = 0.050) volume with rehydration was slower when the 4% beverage was consumed and did not increase to values significantly greater than the dehydrated level (P = 0.013 and P = 0.050 for blood volume and plasma volume, respectively); generally, the increase was an inverse function of the quantity of alcohol consumed. These results suggest that alcohol has a negligible diuretic effect when consumed in dilute solution after a moderate level of hypohydration induced by exercise in the heat. There appears to be no difference in recovery from dehydration whether the rehydration beverage is alcohol free or contains up to 2% alcohol, but drinks containing 4% alcohol tend to delay the recovery process.

Adult↗
PubMed1996

The acute reversal of a diet-induced metabolic acidosis does not restore endurance capacity during high-intensity exercise in man.

The present experiment was designed to investigate whether a diet-induced metabolic acidosis was a major factor in the earlier onset of fatigue during high-intensity exercise. Six healthy males cycled to exhaustion at a workload equivalent to 95 percent of maximum oxygen uptake on four separate occasions. Exercise tests were performed after an overnight fast and each test was preceded by one of four experimental conditions. Two experimental diets were designed, either to replicate each subject's own normal diet [N diet, mean (SD) daily energy intake (E) = 13 (0.7) MJ, 14.5 (0.8) percent protein (Pro), 37.5 (2.2) percent fat (Fat) and 47.5 (2.1) percent carbohydrate (CHO)], or a low-carbohydrate diet [E = 12.6 (0.8) MJ, 33.6 (1.3) percent Pro, 64.4 (1.5) percent Fat and 2.2 (0.4) percent CHO]. These diets were prepared and consumed within the department over a 3-day period. Over a 3-period prior to the exercise trial subjects ingested either NaHCO(3) or CaCO(3) (3.6 and 3.0 mmol*kg body mass), thus giving four experimental conditions: N diet and treatment, N diet and placebo, low-CHO diet and treatment and low-CHO diet and placebo. Treatments were assigned using a randomised protocol. Arterialised venous blood samples were taken for the determination of acid-base status and metabolite concentrations at rest prior to exercise and at intervals for 30 min following exhaustion. Consumption of the low-CHO diet induced a mild metabolic acidosis which was reversed by the ingestion of NaHCO(3). Blood pH, bicarbonate (HCO-(3)) and base excess (BE) were higher following NaHCO(3) ingestion after the normal diet than all of the other experimental conditions (P <0.01). Exercise time following the low-CHO diet was less than on the normal diet conditions (P <0.05): bicarbonate ingestion had no effect on exercise time on either of the diet conditions. Post-exercise blood pH, HCO-(3); and BE were higher following the ingestion of NaHCO(3) irrespective of the pre-exercise diet (P <0.05). Blood lactate concentration was higher 2 min after exercise following the N diet with NaHCO(3) when compared to the low-CHO diets with either NaHCO(3) or placebo (P <0.05). Plasma ammonia accumulation was not significantly different between experimental conditions. These data confirm previous data showing that the ingestion of a low-CHO diet reduces the capacity to perform high-intensity exercise, but it appears that the metabolic acidosis induced by the low-CHO diet is not the cause of the reduced exercise capacity observed during high-intensity exercise under these conditions.

Acid-Base Equilibrium↗
PubMed1996

The effects of induced alkalosis on the metabolic response to prolonged exercise in humans.

To examine the effects of alkalosis on the metabolic response to prolonged exercise, seven healthy males cycled for 1 h at approximately 70% of maximum oxygen uptake on two occasions, 1-week apart. Starting 3 h prior to exercise, subjects consumed either CaCO3 (placebo) or NaHCO3 (0.3 g.kg-1 body mass) over a 2-h period. Arterialised-venous blood samples were drawn before and during exercise for the determination of acid-base status and blood metabolites (lactate, glucose, glycerol and plasma free fatty acids). Expired gas was collected during exercise for determination of oxygen uptake (VO2) and respiratory exchange ratio to estimate fuel oxidation rates. Ratings of perceived exertion (RPE) and heart rates were also recorded. A significant (P < 0.01) alkalosis was observed at all times following bicarbonate ingestion. Blood lactate was significantly (P < 0.05) higher at all sample times throughout exercise following bicarbonate ingestion. Blood lactate concentration [mean (SEM)] reached peak values of 2.90 (0.16) and 4.24 (0.45) mmol.l-1 following 20 min of exercise following placebo and bicarbonate, respectively. No differences between treatments were noted at any time for the other metabolites. VO2 and RPE were significantly higher (P < 0.01) with the bicarbonate trial. At a constant power output increases in VO2 are generally associated with increases in fat oxidation, however, no evidence for an altered fuel oxidation was obtained in the present study. The differences in blood lactate indicate that induced alkalosis increased lactate efflux from muscle, but it cannot be confirmed whether this represents an increased rate of glycolysis within the muscle.

Adult↗
PubMed1996

Restoration of fluid balance after exercise-induced dehydration: effects of food and fluid intake.

This study investigated the effects of post-exercise rehydration with fluid alone or with a meal plus fluid. Eight healthy volunteers (five men, three women) were dehydrated by a mean of 2.1 (SEM 0.0)% of body mass by intermittent cycle exercise in a warm [34 (SEM 0) degrees C], humid [55 (SEM 1)% relative humidity] environment. Over 60 min beginning 30 min after exercise, the subjects ingested a commercially-available sports drink (21 mmol.l-1 Na+, 3.4 mmol.l-1 K+, 12 mmol.l-1 Cl-) on trials A and B: on trial C a standard meal [63 kJ.kg-1 body mass (53% CHO, 28% fat, 19% protein; 0.118 mmol.kJ-1 Na+, 0.061 mmol.kJ-1 K+)] plus drink (1 mmol.l-1 Na+, 0.4 mmol.l-1 K+, 1 mmol.l-1 Cl-) were consumed. Water intake (in millilitres) was 150% of the mass loss (in grams). The trials took place after an overnight fast and were separated by 7 days. Blood and urine samples were collected at intervals throughout the study. Blood was analysed for haematocrit, haemoglobin concentration, serum osmolality, Na+, K+ and Cl- concentrations and plasma angiotensin II concentration. Urine volume, osmolality and electrolyte concentrations were measured. Dehydration resulted in a mean 5.2 (SEM 1.3)% reduction in plasma volume. With the exception of serum osmolality, which was higher on trial B than A at the end of the rehydration period, no differences were recorded for any of the measured parameters between trials A and B. Cumulative urine output following rehydration was lower (P < 0.01) on trial C [median 665 (range 396-1190)ml] than on trial B [median 934 (range 550-1403)ml] which was not different (P = 0.44) from trial A [median 954 (range 474-1501)ml]. Less urine was produced over the 1-h period ending 2 h after rehydration on trial C than on B (P = 0.01). On trials A and B the subjects were in net negative fluid balance by 337 (range 779-minus 306) ml and 373 (range 680-minus 173)ml, respectively (P < 0.01): on trial C the subjects were no different from their initial euhydrated state [median minus 29 (range minus 421-137)ml] 6 h after the end of rehydration (P = 1.00). A larger fraction of total water intake was retained when the standard meal plus drink was consumed. This may have been due to the larger quantities of Na+ and K+ ingested with the meal [mean 63 (SEM 4) mmol Na+, 21.3 (SEM 1.3)mmol K+] than with the drink [mean 42(SEM 2)mmol Na+, 6.8 (SEM 0.4)mmol K+]. There was no difference between trials B and C in any of the measured blood parameters, but urinary Na+ and K+ excretion were both higher on trial C and B. These results suggest that post-exercise fluid replacement can be achieved by ingestion of water if consumed in sufficient volume together with a meal providing significant amounts of electrolytes.

Adult↗
PubMed1996

Post-exercise rehydration in man: effects of volume consumed and drink sodium content.

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.

Adult↗
PubMed1996

Effects of ingested fluids on exercise capacity and on cardiovascular and metabolic responses to prolonged exercise in man.

It is well established that the ingestion of carbohydrate-containing drinks can improve the performance of prolonged exercise. The present study examined the effects of ingestion of water and two dilute glucose-electrolyte drinks on exercise performance and on cardiovascular and metabolic responses to exercise. Twelve subjects exercised to exhaustion on a cycle ergometer at a workload corresponding to 70% of maximum oxygen uptake (VO2,max) on five occasions each separated by 1 week. The first trial served to accustom subjects to experimental conditions. On one trial, no drinks were given and on the others subjects drank 100 ml every 10 min. Drinks consisted of water, an isotonic glucose-electrolyte solution (I: 200 mmol/l glucose; 35 mmol/l NA2; 310 mosmol/kg) and a hypotonic glucose-electrolyte solution (H: 90 mmol/l glucose; 60 mmol/l Na+; 240 mosmol/kg). Treatment order was randomized. Blood and expired air samples were taken and heart rate and rectal temperature measured at intervals during exercise. Median exercise time was greatest for treatment H (110.3 min) followed by treatment I (107.3 min), water (93.1) and no drink (80.7). Endurance times differed significantly overall, and for pairwise comparisons (P < 0.01) between the no-drink trial and both treatments H and I: a difference between water and no drink was seen at the 5% level. At exhaustion, a significant treatment difference was found for the change in plasma volume, with the greatest decrease (6.7%) on the no-drink trial and the smallest decrease (0.5%) on treatment H. Significant treatment effects were also observed for heart rate, rectal temperature and serum osmolality. The results suggest that the ingestion of glucose-electrolyte drinks can improve exercise performance even when the amount of added glucose is small, and that performance may also be enhanced, albeit to a lesser degree, by ingestion of water.

Adult↗
PubMed1996

Water turnover rates in sedentary and exercising middle aged men.

OBJECTIVE: To assess the effect of exercise on water turnover in endurance trained middle aged men. METHODS: Water turnover was assessed using 2H2O as a tracer for water in six exercising and six sedentary middle aged men over seven consecutive days. The exercising subjects ran on average 14.8 km per day, while the sedentary group did not take part in any regular physical activity. RESULTS: The average median (range) rate of water turnover (ml.d-1) was higher in the exercising group [4673 (4320 to 9606)] than in the sedentary group [3256 (2055 to 4185); P = 0.001]. Although there was a tendency for non-renal water losses (ml.d-1) to be greater in the exercising group [1746 (1241 to 5196)] than in the sedentary group [1223 (1021 to 1950); P = 0.08], the major difference in water loss between the groups was the greater urine output (ml.d-1) in those who exercised [3021 (2484 to 4225)] compared to those who were sedentary [(1883 (925 to 2266); P = 0.001]. CONCLUSIONS: The results suggest that fluid intake in middle aged men who exercise regularly must be greater than that of sedentary individuals of the same age group, and that the difference in volume is in excess of that required to replace exercise induced sweat and respiratory water losses.

Adult↗
PubMed1996

Influence of menstrual status on fluid replacement after exercise induced dehydration in healthy young women.

OBJECTIVE: To determine whether fluid replacement after exercise induced dehydration varies over the normal menstrual cycle. METHODS: Five subjects, with a regular menstrual cycle lasting 28 (SEM 2) d, were dehydrated by 1.8(0.1)% of their pre-exercise mass by cycle exercise in the heat. Trials were undertaken 2 d before (trial -2) and 5 and 19 d after the onset of menses (trials 6 and 20 respectively). After exercise, subjects ingested a fixed volume, equivalent to 150% of mass loss, of a commercially available sports drink over a 60 min period. RESULTS: Cumulative urine output [median (range)] over the 6 h following ingestion was the same on all trials: 714(469-750) ml on trial -2; 476(433-639) ml on trial 6; 534(195-852) ml on trial 20. There was no menstrual cycle effect on urinary electrolyte (Na+, K+, Cl-) excretion or serum electrolyte (Na+, K+, Cl-) concentrations. Plasma volume increased by 8-12% of the postexercise value following rehydration. The percentage of ingested fluid retained did not differ between trials at any time. Six hours after drink ingestion, net fluid balance was not different from the initial value on any of the trials. CONCLUSIONS: Acute replacement of exercise induced fluid losses is not affected by the normal menstrual cycle.

Adult↗