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Catecholamine reuptake inhibition improves the performance of male volunteers exercising in warm conditions, but sex differences in thermoregulation, circulating hormones, and central neurotransmission may alter this response. With local ethics committee approval, nine physically active women (mean ± SD age 21 ± 2 years; height 1.68 ± 0.08 m; body mass 64.1 ± 6.0 kg; VO 2peak 51 ± 7 mL/kg/min) were recruited to examine the effect of pre-exercise administration of Bupropion (BUP; 4 × 150 mg) on prolonged exercise performance in a warm environment. Participants completed a VO 2peak test, two familiarization trials, and two randomized, double-blind experimental trials. All trials took place during the first 10 days of the follicular phase of the menstrual cycle. Participants cycled for 1 h at 60% VO 2peak followed by a 30-min performance test. Total work done was greater during the BUP trial (291 ± 48 kJ) than the placebo trial (269 ± 46 kJ, P = 0.042, d = 0.497). At the end of the performance test, core temperature was higher on the BUP trial (39.5 ± 0.4 °C) than on the placebo trial (39.2 ± 0.6 °C, P = 0.021; d = 0.588), as was heart rate (185 ± 9 vs 179 ± 13, P = 0.043; d = 0.537). The results indicate that during the follicular phase of the menstrual cycle, an acute dosing protocol of BUP can improve self-regulated performance in warm conditions., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Hydration status has profound effects on both physical and mental performance, and sports performance is thus critically affected. Both overhydration and underhydration - if sufficiently severe - will impair performance and pose a risk to health. Athletes may begin exercise in a hypohydrated state as a result of incomplete recovery from water loss induced in order to achieve a specific body mass target or due to incomplete recovery from a previous competition or training session. Dehydration will also develop in endurance exercise where fluid intake does not match water loss. The focus has generally been on training rather than on competition, but sweat loss and fluid replacement in training may have important implications. Hypohydration may impair training quality and may also increase stress levels. It is unclear whether this will have negative effects (reduced training quality, impaired immunity) or whether it will promote a greater adaptive response. Hypohydration and the consequent hyperthermia, however, can enhance the effectiveness of a heat acclimation program, resulting in improved endurance performance in warm and temperate environments. Drinking in training may be important in enhancing tolerance of the gut when athletes plan to drink in competition. The distribution of water between body water compartments may also be important in the initiation and promotion of cellular adaptations to the training stimulus., (Copyright © 2013 Nestec Ltd., Vevey/S. Karger AG, Basel.)

The elite athlete represents the extreme of the human gene pool, where genetic endowment is developed by an intensive training programme. Sport encompasses many different activities, calling for different physical and mental attributes. Understanding the physiology of exercise provides insights into normal physiological function.

For each individual, there is a limit to the capacity to perform exercise. The limitation, however, depends on the nature of the task and is also influenced by a number of other factors. Muscle strength is determined largely by muscle mass, specifically muscle cross-sectional area, but is also influenced by neural drive and biomechanical factors. Endurance performance depends on both cardiovascular capacity and the metabolic characteristics of the skeletal muscles. These factors are determined in part by genetic endowment: the elite sprinter has a high proportion of Type 2 muscle fibres while the leg muscles of the successful marathon runner are composes mainly of Type 1 fibres. Whatever the genetic potential, expression of this depends on the intensity, duration and frequency of the applied training stimulus, diet and other factors. The limitation may also depend on environmental factors, such as altitude and temperature.

The purpose of the experiment was to examine whether selective serotonin (5-HT) re-uptake transporter blockade by paroxetine has any effect on perceived effort (RPE) during exercise or the time to reach volitional fatigue and on the prolactin and cortisol responses during prolonged exercise performed in a warm environment. Eight healthy males performed two cycle rides to exhaustion in a warm (32 degrees C) environment at 60% of maximum oxygen uptake. Paroxetine (20 mg) or placebo was administered 5 h before exercise trials in a randomised double blind fashion. Time to exhaustion was not significantly influenced by administration of paroxetine: median (range) time to exhaustion was 93.3 (76.2-175.0) min on the placebo trial and 92.5 (66.0-151.0) min on the paroxetine trial. Rectal temperature was higher at rest and throughout exercise on the paroxetine trial. The serum concentrations of prolactin and cortisol were determined throughout exercise as peripheral markers of central 5-HT activity. RPE increased over time but was not influenced by paroxetine administration. Prolactin and cortisol levels increased over time but paroxetine administration did not influence the hormone responses during exercise. In conclusion, acute administration of paroxetine failed to alter RPE, exercise capacity or the response of the determined peripheral hormone markers of central 5-HT activity during prolonged exercise in a warm environment.

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.

1. This study examined the effects of exercise and diet manipulation intended to alter initial muscle glycogen levels on the capacity to perform prolonged exercise at two ambient temperatures. 2. Six well-trained cyclists participated in randomized order in two diet and exercise regimens each lasting 8 days and comprising four cycle tests to exhaustion at 70 % of maximum oxygen uptake. On days 1 and 5, subjects exercised to exhaustion to deplete muscle glycogen. Three days after each depletion trial a diet providing 10 % (low carbohydrate (CHO)) or 80 % (high CHO) of energy as CHO was consumed, and each diet was followed by a performance trial at the same ambient temperature, either 10 or 30 C (days 4 and 8). This schedule was repeated after a week, but performance trials were carried out at the other ambient temperature. 3. In the cold, cycling time increased (median (range)) from 89.2 min (78.0-129.5 min) on the low CHO trial to 158.2 min (116.9-165.6 min) on the high CHO trial (P < 0.01). In the heat, cycling time increased from 44.0 min (31.8-51.4 min) on the low CHO trial to 53.2 min (50.2-82.2 min) on the high CHO trial (P = 0.02). Total CHO oxidized during exercise in the cold after the low CHO diet was higher than in the heat after either diet suggesting that exercise in the heat was terminated before all available CHO stores had been emptied.

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.

The present study examined the hypothesis that creatine (Cr) supplementation can increase the performance of isometric exercise in subjects engaged in a strength training program. Ten male subjects were tested in three experimental trials 7 days apart (days 1, 8 and 15). In each trial the subjects' maximum voluntary force of contraction (MVC) was measured in both legs and isometric endurance capacity at 80, 60, 40 and 20% of MVC of their stronger leg (knee extensor group) was measured with a 4-min rest between contractions. Additionally, the subjects' isometric endurance capacity at 80% of MVC of their weaker leg was measured in 10 repeated bouts interspersed with 2-min rest. A double-blind cross-over design was adopted for administering Cr or placebo. Subjects were randomized into either the Cr-placebo (Group A: days 2-6: 10 g day-1 of Cr; days 9-13: 10 g day-1 of glucose polymers) or the placebo-Cr group (Group B reverse supplementation order). The daily diet was analysed, and urine samples from 24-h collections were subjected to Cr and creatinine analysis. In each subject, approximately 18 g (35%) of Cr was eliminated in the urine during the Cr supplementation period. MVC increased by about 10% (P < 0.01 in the weaker leg, P < 0.05 in the stronger leg) and body mass increased by 1.7 +/- 0.4 kg (2.3%, P < 0.01) and 1.8 +/- 0.3 kg (2.1%, P < 0.01) in groups A and B, respectively, after Cr supplementation, while energy intake and diet composition remained constant throughout the study. The subjects' endurance capacity increased (P < 0.05) in all the bouts after Cr supplementation. Muscle hypertrophy in response to Cr supplementation and weight training may explain the findings of the present study.

A number of peripheral indices of serotonergic function were examined in endurance-trained (ET) and sedentary males using the blood platelet as a model of the serotonergic neurone. The aim of the study was to investigate possible involvement and adaptation of the central serotonergic system in exercise-induced fatigue. The [3H] paroxetine-defined density of platelet serotonin transporters, platelet serotonin content and the plasma concentration of amino acids were determined in 10 ET and eight sedentary males. The mean (standard deviation) density of the serotonin transporter in the platelet membranes of the ET subjects was greater [1237 (182) fmol mg protein-1] than that of the sedentary subjects [910 (119) fmol mg protein-1; P = 0.013]. No difference (P = 0.51) could be seen between the median (range) platelet serotonin content of the ET subjects [0.98 (0.37-3.04) nmol platelet-10] and that of the sedentary subjects [0.82 (0.18-1.49) nmol platelet-10]. The platelet poor plasma concentrations of tryptophan and tyrosine were lower in the ET subjects (P = 0.028 and 0.015, respectively). The present study suggests that the platelet membrane of the ET subjects has a greater density of the serotonin transporter and that this is inversely related to the circulating concentration of the serotonin precursor, tryptophan. It remains to be resolved whether the increase in serotonin transporter density in the platelet membrane of ET subjects is reflected centrally and whether the ET platelet population may be sufficiently different from that of sedentary individuals to alter serotonin transporter density.

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 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.

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.

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.

Seven healthy subjects exercised to exhaustion on a bicycle ergometer at a power output corresponding to 70% of maximum oxygen uptake after administration of either a placebo or 20 mg of paroxetine, a serotonin re-uptake inhibitor. Exercise time after paroxetine (median 94 min; range 84-127 min) was less (P < 0.05) than after placebo (median 116 min; range 86-133 min). The metabolic and cardiorespiratory responses to exercise were the same in both trials. This result supports the suggestion that there is a central component to fatigue which is mediated by the activity of serotoninergic neurones.

1. Blood antioxidants were measured in venous blood samples from 20 runners and six sedentary individuals. All subjects were male, between 20 and 40 years old, and in steady state with respect to body weight and physical activity patterns. Dietary analysis was undertaken using a 7-day weighed food intake. Correlations were sought between antioxidants in blood and (1) weekly training distance and (2) maximum oxygen uptake. In addition, 12 runners could be classified into two groups undertaking either low (range 16-43 km, n = 6) or high (80-147 km, n = 6) weekly training. 2. Body weight (range 55.3-90.0 kg) and percentage body fat (range 7-19%) both showed negative correlations with the weekly training distance (both P less than 0.001). Energy intake and maximum oxygen uptake were both correlated with the weekly training distance (both P less than 0.001). 3. Plasma creatine kinase activity, an indicator of muscle damage, was significantly correlated with the weekly training distance (P less than 0.01), whereas the plasma concentration of thiobarbituric acid-reactive substances, an indicator of free-radical-mediated lipid peroxidation, decreased with increased maximum oxygen uptake (P less than 0.01). 4. Erythrocyte alpha-tocopherol content was greater in the two running groups (P less than 0.05) compared with the sedentary group, and lymphocyte ascorbic acid concentration was significantly elevated in the high-training group (P less than 0.01) compared with the low-training group. 5. Erythrocyte activities of the antioxidant enzymes, glutathione peroxidase and catalase, were significantly and positively correlated with the weekly training distance (P less than 0.01 and P less than 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of a competitive marathon race on serum biochemical and haematological parameters have been evaluated. Blood samples were obtained shortly before and immediately after the race; urine samples were also obtained before and after the race. Body weight was recorded pre- and post-race. During the race subjects consumed a total of 1.41 of either water or a dilute glucose-electrolyte solution. The average weight loss of the runners was 2.09 +/- 0.77 kg (mean +/- SD), corresponding to 2.9 +/- 0.8% of body weight. Small but significant increases in both haematocrit and haemoglobin concentration occurred; plasma volume was calculated to decrease by 4.7%. Serum potassium concentration showed no change, but the response was highly variable; serum sodium concentration increased in line with the decrease in plasma volume. In the group of subjects drinking water during the race, the pre-race plasma glucose concentration was 5.3 +/- 1.2 mmol . l-1, this was unchanged after the race (5.0 +/- 1.2 mmol . l-1). A significant increase (P less than 0.01) in the plasma glucose concentration, from 5.2 +/- 0.6 to 6.0 +/- 1.5 mmol . l-1 occurred in the group of subjects drinking the glucose-electrolyte solution. Apart from this, there were no significant differences between the two groups.

The capacity to perform isometric and dynamic muscle contractions at different forces has been measured in two separate groups of subjects: 25 men and 25 women performed sustained isometric contractions of the knee-extensor muscles of their stronger leg to fatigue, at forces corresponding to 80%, 50% and 20% of the maximum voluntary force of contraction (MVC). The second experimental model involved a bilateral elbow-flexion weight lifting exercise. Eleven women and 12 men performed repetitions at loads corresponding to 90%, 80%, 70%, 60% and 50% of maximum load (1RM), at a rate of 10 X min-1 to the point of fatigue. Males were stronger (p less than 0.001) than females in both the static (675 +/- 120 N vs 458 +/- 80 N; mean +/- SD) and dynamic (409 +/- 90 N vs 190 +/- 33 N) contractions. Isometric endurance time of the males at a force corresponding to 20% of MVC was less than that of the females (180 +/- 51 s vs 252 +/- 56 s; p less than 0.001) but there was no difference between the sexes at 50% or 80% of MVC. Similarly, when the sexes were compared using dynamic elbow-flexion exercise, the female subjects were able to perform a greater number of repetitions than males at loads of 50% (p less than 0.005), 60% (p less than 0.001) and 70% (p less than 0.025) of 1RM, but there was no difference between the sexes at loads of 80% or 90% of 1RM.(ABSTRACT TRUNCATED AT 250 WORDS)

Seven healthy male subjects exercised to exhaustion at a workload equivalent to 100% of their maximal oxygen uptake (VO2max) on 3 separate occasions. Each high intensity exercise test was performed on an electrically braked cycle ergometer; the first took place after a normal diet (46 +/- 8% carbohydrate (CHO), 41 +/- 7% fat and 13 +/- 3% protein); the second after 3 days of a low CHO diet (7 +/- 3% CHO, 64 +/- 5% fat and 29 +/- 4% protein) and the third after 3 days of a high CHO diet (76 +/- 6% CHO, 14 +/- 5% fat and 10 +/- 2% protein). Acid-base status and selected metabolites were measured on arterialized venous blood at rest prior to exercise and during the post-exercise period. Plasma urea concentration and urine total acidity were measured on each day of the experiment. Exercise time to exhaustion was longer after the normal (p less than 0.05) and high (p less than 0.01) CHO diets compared with the low CHO diet. Pre-exercise plasma bicarbonate concentration and blood PCO2 were higher after the high CHO diet when compared with the normal (p = 0.05, p less than 0.05 respectively) and low CHO conditions (p less than 0.05, p less than 0.05 respectively). Pre-exercise bicarbonate was also higher after the normal CHO diet when compared with the low CHO diet (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The availability of carbohydrate (CHO) as a substrate for the exercising muscles is known to be a limiting factor in the performance of prolonged cycle exercise, and provision of exogenous CHO in the form of glucose can increase endurance capacity. The present study examined the effects of ingestion of fluids and of CHO in different forms on exercise performance. Six male volunteers exercised to exhaustion on a cycle ergometer at a workload which required approximately 70% of Vo2max. After one preliminary trial, subjects performed this exercise test on six occasions, one week apart. Immediately before exercise, and at 10-min intervals throughout, subjects ingested 100 ml of one of the following: control (no drink), water, glucose syrup, fructose syrup, glucose-fructose syrup or a dilute glucose-electrolyte solution. Each of the syrup solutions contained approximately 36 g CHO per 100 ml; the isotonic glucose-electrolyte solution contained 4 g glucose per 100 ml. A randomised Latin square order of administration of trials was employed. Expired air samples for determination of Vo2, respiratory exchange ratio and rate of CHO oxidation were collected at 15-min intervals. Venous blood samples were obtained before and after exercise. Subjects drinking the isotonic glucose-electrolyte solution exercised longer (90.8 (12.4) min, mean (SEM] than on the control test (70.2 (8.3) min; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Six men were studied during exercise to exhaustion on a cycle ergometer at 73% of VO2max following ingestion of glycerol, glucose or placebo. Five of the subjects exercised for longer on the glucose trial compared to the placebo trial (p less than 0.1; 108.8 vs 95.9 min). Exercise time to exhaustion on the glucose trial was longer (p less than 0.01) than on the glycerol trial (86.0 min). No difference in performance was found between the glycerol and placebo trials. The ingestion of glucose (lg X kg-1 body weight) 45 min before exercise produced a 50% rise in blood glucose and a 3-fold rise in plasma insulin at zero min of exercise. Total carbohydrate oxidation was increased by 26% compared to placebo and none of the subjects exhibited a fall in blood glucose below 4 mmol X 1-1 during the exercise. The ingestion of glycerol (lg X kg-1 body weight) 45 min before exercise produced a 340-fold increase in blood glycerol concentration at zero min of exercise, but did not affect resting blood glucose or plasma insulin levels; blood glucose levels were up to 14% higher (p less than 0.05) in the later stages of exercise and at exhaustion compared to the placebo or glucose trials. Both glycerol and glucose feedings lowered the magnitude of the rise in plasma FFA during exercise compared to placebo. Levels of blood lactate and alanine during exercise were not different on the 3 dietary treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of variations in muscle fibre composition on isometric endurance capacity was measured in 23 young healthy untrained male volunteers. After determination of the maximum voluntary force of contraction (MVC), subjects sustained to fatigue contractions at forces of 80%, 50% and 20% of MVC with a 5-min rest between each. A needle biopsy was obtained from m. vastus lateralis and used for histochemical determination of fibre composition based on myosin ATP-ase activity, and fibre are a based on succinate dehydrogenase (SDH) activity. Endurance times were 21 +/- 9 s (mean +/- SD) at 80% of MVC, 56 +/- 17 s at 50% of MVC and 203 +/- 89 s at 20% of MVC. A wide range of muscle fibre compositions was observed with Type I fibres accounting for 48.0 +/- 10.5% of the total, corresponding to 45.0 +/- 11.5% of the total muscle area. Muscle fibre composition, whether expressed as the proportions of the different fibre types present, or as the fraction of total muscle cross-sectional area occupied by each fibre type was not correlated with isometric endurance capacity at any of the three forces studied. Endurance time was also unrelated to MVC. In contrast to the results of previous studies where trained subjects were used, or where different muscle groups were compared, these results suggest that isometric endurance is not influenced by muscle fibre composition.

Coulter profiles with differential white cell counts, serum ferritin, and haptoglobin levels were determined in venous blood samples obtained from 90 males (M) and 25 females (F) immediately before and after completion of a competitive marathon (42.2 km) race. In an additional 20 male runners, the same measurements were performed serially during the 24 h following their completion of the race. In the pre-race samples from 90 M and 25 F, hypoferritinemia was present in 4/22 M and 1 F found to be mildly anemic. Neutropenia was detected in 4 M and 3 F and mild thrombocytopenia in 2 M. Haptoglobin levels were normal in all the female runners but reduced (less than 0.3 g/l) in 6 M. All post-race samples (88 M and 25 F) were characterized by a reactive neutrophilia and thrombocytosis including those with pre-race neutropenia or thrombocytopenia. An unexpected and incompletely explained sex difference in packed cell volume (PCV) response was observed. In males, the mean PCV increased from 0.425 +/- 0.021 to 0.444 +/- 0.028 (P less than 0.0001) whereas in females it decreased from 0.437 +/- 0.029 to 0.423 +/- 0.036 (P less than 0.05). In the post-race samples, anhaptoglobinemia was found in 13/88 M and 4/25 F. In the 20 male runners studied serially for 24 h after the race, the major changes involved a progressive increase in mean plasma volume (17.4% +/- 12.2% at 24 h) compared with the pre-race value, a progressive and significant increase in MCH and MCHC probably indicating a loss in red cell water and the gradual reversion of the reactive neutrophilia and thrombocytosis to basal levels.