Independent and combined effects of liquid carbohydrate/essential amino acid ingestion on hormonal and muscular adaptations following resistance training in untrained men

This investigation examined chronic alteration of the acute hormonal response associated with liquid carbohydrate (CHO) and/or essential amino acid (EAA) ingestion on hormonal and muscular adaptations following resistance training. Thirty-two untrained young men performed 12 weeks of resistance training twice a week, consuming ~675 ml of either, a 6% CHO solution, 6 g EAA mixture, combined CHO + EAA supplement or placebo (PLA). Blood samples were obtained pre- and post-exercise (week 0, 4, 8, and 12), for determination of glucose, insulin, and cortisol. 3-Methylhistidine excretion and muscle fibre cross-sectional area (fCSA) were determined pre- and post-training. Post-exercise cortisol increased (P<0.05) during each training phase for PLA. No change was displayed by EAA; CHO and CHO + EAA demonstrated post-exercise decreases (P<0.05). All groups displayed reduced pre-exercise cortisol at week 12 compared to week 0 (P<0.05). Post-exercise insulin concentrations showed no change for PLA; increases were observed for the treatment groups (P<0.05), which remained greater for CHO and CHO + EAA (P<0.001) than PLA. EAA and CHO ingestion attenuated 3-methylhistidine excretion 48 h following the exercise bout. CHO + EAA resulted in a 26% decrease (P<0.01), while PLA displayed a 52% increase (P<0.01). fCSA increased across groups for type I, IIa, and IIb fibres (P<0.05), with CHO + EAA displaying the greatest gains in fCSA relative to PLA (P<0.05). These data indicate that CHO + EAA ingestion enhances muscle anabolism following resistance training to a greater extent than either CHO or EAA consumed independently. The synergistic effect of CHO + EAA ingestion maximises the anabolic response presumably by attenuating the post-exercise rise in protein degradation.An erratum to this article can be found at     

The effects of a glycogen loading regimen on acid-base status and blood lactate concentration before and after a fixed period of high intensity exercise in man

Summary Six healthy male subjects exercised after an overnight fast for a fixed 3 min period at a workload equivalent to 100% of their maximal oxygen uptake ( ) on 3 separate occasions. The first test took place after subjects had consumed a mixed diet (43±3% carbohydrate (CHO), 41±5% fat and 16±3% protein) for 3 days, and was followed 2 h later by prolonged cycling to exhaustion at 77±3% to deplete muscle glycogen stores. Following this, subjects consumed a low CHO diet (4±1% CHO, 63±5% fat and 33±6% protein) for the remainder of the day and for the subsequent 2 days; on the morning of the next day a second high intensity test took place. Finally subjects followed a 3 day high CHO diet (73±7% CHO, 17±6% fat and 10±1% protein) before their last test. Acid-base status and selected metabolites were measured on arterialised-venous blood at rest prior to exercise and at intervals for 15 min following exercise. Prior to exercise, plasma pH and blood lactate concentration were higher (p<0.05) after the high CHO diet when compared with the low CHO diet. Pre-exercise plasma bicarbonate, blood PCO₂ and blood base excess were all higher after the high (p<0.001,p<0.01,p<0.01 respectively) and normal (p<0.05,p<0.05,p<0.05 respectively) CHO diets when compared with the low CHO diet. During the post-exercise period there were no differences in plasma pH or blood base excess between the three experimental situations; plasma bicarbonate was higher (p<0.05) at 2 min post-exercise after the high CHO diet when compared with the low CHO diet; blood PCO₂ was higher throughout the post-exercise period after the high CHO diet when compared with the low CHO diet and at 2 min post-exercise was higher after the normal CHO diet than after the low CHO diet (p<0.5). The post-exercise blood lactate concentration after the high CHO diet was at all times higher than the corresponding values recorded after the normal CHO diet and until 15 min post-exercise was significantly higher than the values recorded after the low CHO diet. The present experiment further substantiates the view that a pattern of dietary and exercise manipulation can significantly influence the acid-base status of the blood and by doing so may influence high intensity exercise performance.     

Effects of carbohydrate feedings on plasma free tryptophan and branched-chain amino acids during prolonged cycling

Summary Brain serotonin (5-hydroxytryptamine, 5-HT) has been suggested to be involved in central fatigue during prolonged exercise. Changes in the ratio of plasma free tryptophan (free Trp) to branched-chain amino acids (BCAA) are associated with altered brain 5-HT synthesis. The purposes of this study were to describe systematically the effects of prolonged exercise on changes in plasma free Trp and BCAA and to examine the effects of carbohydrate (CHO) feedings on these same variables. Eight well-trained men [ _max = 57.8 (SE 4.1) ml kg^–1 min^–1] cycled for up to 255 min at a power output corresponding toVO₂ at lactate threshold (approximately 68%VO_2max) on three occasions separated by at least 1 week. Subjects drank 5 ml kg^–1 body wt^–1 of either a water placebo, or a liquid beverage containing a moderate (6% CHO) or high (12% CHO) concentration of carbohydrate beginning at min 14 of exercise and every 30 min thereafter. Exercise time to fatigue was shorter in subjects receiving placebo [190 (SE 4) min] as compared to 6% CHO [235 (SE 10) min] and 12% CHO [234 (SE 9) min] (P<0.05). Glucose and insulin decreased in the placebo group, and free Trp, free-Trp/BCAA, and free fatty acids increased approximately five- to sevenfold (P < 0.05). These changes were attenuated in a dose-related manner by the carbohydrate drinks. Plasma free Trp and plasma free fatty acids were highly correlated (r=0.86,P<0.001). Plasma BCAA did not change in the placebo group, but decreased slightly in those receiving 6% CHO and 12% CHO (P<0.05). No differences in heart rate, , plasma volume and respiratory exchange ratio were found. The results indicate that free Trp and free Trp/BCAA increase progressively during prolonged cycling to fatigue. This response was attenuated by CHO feedings. Changes in plasma free fatty acids probably play a prominent role in these responses.     

The effects of carbohydrate supplementation during the second of two prolonged cycling bouts on immunoendocrine responses

The purpose of this study was to examine the effect of carbohydrate (CHO) feeding during the second of two 90-min cycling bouts (EX1 started at 09:00 and EX2 started at 13:30) at 60% on leucocyte redistribution, neutrophil degranulation and oxidative burst and plasma IL-6 and stress hormone responses. This study consisted of two trials, which were completed in a counterbalanced order and separated by at least 4 days. Subjects (n=9) consumed a lemon flavoured 10% w/v CHO (glucose) or placebo (PLA) beverage during EX2: 500 ml just before exercise and 250 ml every 20 min during exercise. Venous blood samples were taken 5 min before exercise, immediately post-exercise, and 18-h post-EX2 for both trials. The main findings of this study were that ingestion of CHO compared with PLA during EX2 better maintained plasma glucose concentration, blunted the responses of plasma adrenaline, ACTH, cortisol, GH and IL-6, and attenuated the leukocytosis and monocytosis, but had no effect on neutrophil degranulation and oxidative burst activity. Furthermore, the immunoendocrine disturbances induced by two bouts of prolonged exercise returned to resting values within 18 h. These findings suggest that ingestion of CHO compared with PLA during the second of two bouts of 90-min cycling at 60% better maintains plasma glucose, blunts hypothalamic–pituitary–adrenal activation, and attenuates leucocyte trafficking, but does not affect neutrophil function. Furthermore, the disturbances of immunoendocrine responses induced by two bouts of prolonged exercise on the same day recover within 18 h.     

Mobilization and oxidative burst of neutrophils are influenced by carbohydrate supplementation during prolonged cycling in humans

Prolonged, strenuous exercise may lead to suppressive effects on the immune system, which might be responsible for a greater susceptibility to opportunistic infections. The aim of this study was to examine the influence of carbohydrate substitution (CHS) during prolonged, strenuous exercise on neutrophil granulocytes and their oxidative burst (intracellular oxidation of dihydrorhodamine₁₂₃ to rhodamine₁₂₃ after induction by formylized 1-methionyl-1-leucyl-1-phenylalanin) using flow cytometry. In three trials different concentrations of CHS (placebo compared to 6% and 12% CHS; 50 ml·kg^–1) were given randomly to 14 endurance trained cyclists [mean (SD) age 25 (5) years, maximal oxygen uptake 67 (6) ml·min^–1·kg^–1] cycling for 4 h in a steady state at 70% of their individual anaerobic threshold. Blood samples were taken before, immediately after cessation, 1 h and 19 h after exercise. A significant rise in neutrophil counts was observed immediately after cessation and 1 h after exercise with a return to normal rest values 19 h after exercise for all three conditions (P<0.001). The relative proportions of rhodamine₁₂₃+ neutrophils were significantly diminished in all three conditions 1 h after exercise (P<0.01), while the mean fluorescence intensity was lowest in the placebo trial and differed significantly to the 12% CHS trial (P=0.024) and almost significantly to the 6% CHS trial (P=0.052). In conclusion, these data suggest a beneficial effect of CHS on the neutrophil oxidative burst and a possible attenuation of the susceptibility to infections, presumably due to the reduction of metabolic stress in prolonged, strenuous exercise. Electronic Publication     

Post-exercise vitamin C supplementation and recovery from demanding exercise

The aim of this study was to investigate whether post-exercise vitamin C supplementation influences recovery from an unaccustomed bout of exercise. Sixteen male subjects were allocated to either a placebo (P; n=8) or vitamin C (VC) group (n=8). Subjects performed a prolonged (90-min) intermittent shuttle-running test, and supplementation began after the cessation of exercise. Immediately after exercise the VC group consumed 200 mg of VC dissolved in a 500 ml drink, whereas the subjects in the P group consumed the drink alone. Later on the same day and then in the morning and evening of the following 2 days, subjects consumed additional identical drinks. Plasma VC concentrations in the VC group increased above those in the P group 1 h after exercise and remained above P values for the 3 days after exercise. Nevertheless, post-exercise VC supplementation was not associated with improved recovery. Post-exercise serum creatine kinase activities and myoglobin concentrations were unaffected by supplementation. Muscle soreness and the recovery of muscle function in the leg flexors and extensors were not different in VC and P groups. Furthermore, although plasma concentrations of interleukin-6 and malondialdehyde increased following exercise, there was no difference between VC and P groups. These results suggest that either free radicals are not involved in delaying the recovery process following a bout of unaccustomed exercise, or that the consumption of VC wholly after exercise is unable to deliver this antioxidant to the appropriate sites with sufficient expediency to improve recovery. Electronic Publication     

Dietary composition and acid-base status: limiting factors in the performance of maximal exercise in man?

Summary Seven healthy male subjects exercised to exhaustion at a workload equivalent to 100% of their maximal oxygen uptake ( ) 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 arterialised 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<0.05) and high (p<0.01) CHO diets compared with the low CHO diet. Pre-exercise plasma bicarbonate concentration and blood were higher after the high CHO diet when compared with the normal (p=0.05, p<0.05 respectively) and low CHO conditions (p<0.05, p<0.05 respectively). Pre-exercise bicarbonate was also higher after the normal CHO diet when compared with the low CHO diet (p<0.05). Mean dietary acid intake for each 3 day period of dietary variation and plasma urea immediately prior to exercise were lower after the high CHO diet when compared to both normal (p<0.01, p<0.01) and low (p<0.01, p<0.001) CHO diets. They were also lower (p<0.01, p<0.01) after the normal when compared with the low CHO diet. Urine total acidity was higher after the low CHO diet when compared with both the normal (p<0.01) and high CHO (p<0.01) diets and near significance was found (p<0.06) when comparing the normal and high CHO diets. The present exsuggests that dietary variation alone can significantly affect the acid-base balance of the blood and may thereby influence endurance time during high intensity exercise.     

The effect of 2 weeks vitamin C supplementation on immunoendocrine responses to 2.5 h cycling exercise in man

An increased systemic concentration of stress hormones (of the hypothalamic-pituitary adrenal axis) and some cytokines may contribute to the depression of immune cell function typically observed after prolonged exercise. The aim of the present study was to determine the effect of 2 weeks of supplementation with vitamin C (VC) on cortisol, adrenocorticotrophic hormone, interleukin-6, oxidative stress and neutrophil responses to a single bout of endurance exercise. Nine healthy endurance-trained males exercised for 2.5 h at 60% after 2 weeks of placebo (PLA) or VC (1,000 mg day⁻¹) supplementation. All participants completed both trials utilising a randomised crossover design with a minimum 14 day washout period between trials. There was a significant trial × time interaction effect for plasma cortisol concentration (P = 0.039) which tended to be lower in the VC trial but post hoc analysis found no specific between trial differences. There was a significantly lower post-exercise neutrophilia (P < 0.014) in the VC trial, compared with the PLA trial. There was no trial × time interaction for measures of neutrophil function (bacteria-stimulated elastase release, fMLP or PMA-stimulated oxidative burst). However, there was a trend for higher fMLP-stimulated neutrophil oxidative burst in the VC compared with PLA trial (trial × time interaction, P = 0.075). These results suggest that supplementation with VC for a period of up to 2 weeks provides little to no protection against the depression of neutrophil function which typically occurs after endurance exercise.     

Carbohydrate ingestion during prolonged running exercise results in an increase of serum cortisol and decrease of gonadotrophins

We tested the hypothesis that improved availability of energy through carbohydrate ingestion could counteract the documented suppression of pituitary-gonadal function during prolonged exercise. Nine trained males repeated twice a 36 kilometre running exercise with two weeks interval. During the tests the subjects ingested in a randomized single-blind fashion a total of 1050 millilitres of carbohydrate and placebo solutions. The total amount of ingested carbohydrate was 105 grams. Venous blood samples were taken before the exercise (sample A), immediately after exercise (B), and 2 hours later (C). In the B samples plasma glucose was 14% higher (P less than 0.01) and serum cortisol 13% higher (P less than 0.05) in the carbohydrate than in the control trial. In contrast, the level of LH was 18% (P less than 0.05) and that of FSH 11% lower (P less than 0.05) in the carbohydrate than in the placebo trial. Serum testosterone concentration did not differ between the treatment groups. We conclude that carbohydrate ingestion does not counteract the exercise-associated suppression of gonadotrophin secretion, but results in paradoxical increase of serum cortisol and decrease of LH and FSH, in comparison to placebo-treated controls. The higher cortisol level in carbohydrate group may be secondary to higher insulin levels.     

Effect of carbohydrate ingestion on exercise performance and carbohydrate metabolism in persons with spinal cord injury

Carbohydrate ingestion during exercise and as a pre-exercise bolus improves exercise performance in able-bodied athletes. Little is known about the potential for carbohydrate ingestion to improve exercise performance in athletes with spinal cord injury (SCI), nor the potential physiological limitations of such a practice resulting from an SCI. Therefore, this study investigated the effects of carbohydrate ingestion on exercise performance in physically active and athletic persons with SCI. Six participants with complete SCI (neurological level of lesion ranging from C₆ to T₇) and normal glucose tolerance were studied twice during 60 min of arm cranking at 65% of peak oxygen consumption followed by a 20-min time trial with the ingestion of either a carbohydrate drink (CHO trial: 0.5 g CHO kg^?1 body weight in 500 ml) or placebo (PLA trial) applied in a double-blind counter-balanced manner. The participants with tetraplegia had sufficient neurological function to permit voluntary arm-cranking exercise. There was no difference in time-trial performance between CHO and PLA trials (P > 0.05). The results suggest that carbohydrate ingestion in persons with SCI does not improve exercise performance.     

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% 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)% protein (Pro), 37.5 (2.2)% fat (Fat) and 47.5 (2.1)% carbohydrate (CHO)], or a low-carbohydrate diet [E = 12.6 (0.8) MJ, 33.6 (1.3)% Pro, 64.4 (1.5)% Fat and 2.2 (0.4)% 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 NaHCO₃ or CaCO₃ (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 NaHCO₃. Blood pH, bicarbonate (HCO₃ ^– ) and base excess (BE) were higher following NaHCO₃ 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, HCO₃ ^– and BE were higher following the ingestion of NaHCO₃ irrespective of the pre-exercise diet (P < 0.05). Blood lactate concentration was higher 2 min after exercise following the N diet with NaHCO₃ when compared to the low-CHO diets with either NaHCO₃ 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.     

Exercise induces pentane production and neutrophil activation in humans. Effect of propranolol

Summary The effect of -adrenergic receptor blockade on exercise-induced lipid peroxidation in man has been examined by measuring the production of pentane in expired air. For this purpose, five healthy male subjects were subjected to dynamic exercise of graded intensity on a cycle ergometer (10 min at 45%, 5 min at 60% and 75% maximal oxygen uptake 1 h after ingestion of either a placebo or 40-mg propranolol. At rest, mean pentane concentration ([pent]) with placebo was 4.13 pmol · l^–1, SD 2.14. After exercise, this value significantly increased by 310% (17.1 pmol · l^–1, SD 7.73, P < 0.01). Oral administration of 40-mg propranolol significantly lowered the mean resting [pent] to 1.75 pmol · l^–1, SD 0.77, P < 0.05. After exercise, the increase of [pent] was much smaller (240%) and was less significant (P < 0.2) than with the placebo. The mechanism of this inhibitory effect of propranolol remains to be elucidated. However, as indicated by the measurement of plasma myeloperoxidase concentration, it can be concluded that the antioxidant property of propranolol cannot be attributed to the inhibition of neutrophil activation, a possible source of free radicals during exercise.     

Fuel substrate turnover and oxidation and glycogen sparing with carbohydrate ingestion in non-carbohydrate-loaded cyclists

This study examined the effects of ingesting 500 ml/h of either a 10% carbohydrate (CHO) drink (CI) or placebo (PI) on splanchnic glucose appearance rate (endogenous + exogenous) (R _a), plasma glucose oxidation and muscle glycogen utilisation in 17, non-carbohydrate-loaded, male, endurance-trained cyclists who rode for 180 min at 70% of maximum oxygen uptake. Mean muscle glycogen content at the start of exercise was 130 ± 6 mmol/kg ww; (mean ± SEM). Total CHO oxidation was similar in CI and PI subjects and declined during the trial. R _a increased significantly during the trial (P < 0.05) in both groups. Plasma glucose oxidation also increased significantly during the trial, reaching a plateau in the PI subjects, but was significantly (P < 0.05) higher in CI than PI subjects at the end of exercise [(98 ± 14 vs. 72 ± 10 μmol/min/kg fat-free mass) (FFM) (1.34 ± 0.19 vs. 0.93 ± 0.13 g/min)]. However, mean endogenous R _a was significantly (P < 0.05) lower in the CI than PI subjects throughout exercise (35 ± 7 vs. 54 ± 6 μmol/min/kg FFM), as was the oxidation of endogenous plasma glucose, which remained almost constant in CI subjects, and reached values at the end of exercise of 42 ± 13 and 72 ± 10 μmol/min/kg FFM in the CI and PI groups respectively. Of the 150 g CHO ingested during the trial, 50% was oxidised. Muscle glycogen disappearance was identical during the first 2 h of exercise in both groups and continued at the same rate in PI subjects, however no net muscle glycogen disappearance occurred during the final hour in CI subjects. We conclude that ingestion of 500 ml/h of a 10% CHO solution during prolonged exercise in non carbohydrate loaded subjects has a marked liver glycogen-sparing effect or causes a reduction in gluconeogenesis, or both, maintains plasma glucose concentration and has a muscle glycogen-sparing effect. Received: 25 August 1995/Received after revision: 25 March 1996/Accepted: 29 April 1996     

Effect of altered pre-exercise carbohydrate availability on selection and perception of effort during prolonged cycling

This study assessed the effect of altered carbohydrate (CHO) availability on self-selected work rate during prolonged time-trial cycling. Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 ± 0 g CHO kg⁻¹ day⁻¹) (HC) and (b) low CHO intakes (0.6 ± 0.1 g CHO kg⁻¹ day⁻¹) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials. Self-selected external power output was not different during the first 2 h of exercise between experimental conditions (P > 0.05), despite reported sensations of increased tiredness before and during exercise, significantly reduced whole body CHO oxidation (P < 0.05), plasma lactate concentrations (P < 0.05) and earlier onset of fatigue during exercise in LC versus HC. Perceived exertion was not different throughout exercise between conditions (P > 0.05). Mean power output declined significantly in LC versus HC (P < 0.05) after ∼ 2 h of exercise, and was associated with significant reductions in cadence, heart rate and plasma glucose concentration (P < 0.05). These results demonstrate that when compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise. This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject’s awareness of dietary CHO restriction rather than solely a physiologically mediated action. Further research is required to distinguish the influence of circulating glucose and peripheral glycogen availability on pacing strategy during prolonged exercise.     

Hormonal Influences on Stress-Induced Neutrophil Mobilization in Health and Chronic Fatigue Syndrome

This investigation tested the hypotheses that women diagnosed with chronic fatigue syndrome (CFS) would exhibit significantly greater systemic indices of exercise-induced leukocyte mobilization and inflammation (neutrophilia, lactoferrin release, complement activation) than controls matched for age, weight, and habitual activity and that responses in the luteal phase of the menstrual cycle would be greater than in the follicular phase. Subjects stepped up and down on a platform adjusted to the height of the patella for 15 min, paced by metronome. Blood samples were collected under basal conditions (the day before exercise) and following exercise for determination of circulating neutrophils and plasma concentrations of lactoferrin, C3a des arg, and creatine kinase. Complete, 24-hr urine collections were made for determination of cortisol excretion. For all subjects, circulating neutrophil counts increased 33% (P < 0.0001) and lactoferrin increased 27% (P = 0.0006) after exercise, whereas plasma C3a des arg and creatine kinase did not increase. No indication of an exaggerated or excessive response was observed in the CFS patients compared to the controls. In healthy women, circulating neutrophil numbers exhibited previously described relationships with physiological variables: basal neutrophil counts correlated with plasma progesterone concentrations (R = 0.726, P = 0.003) and the exercise-induced neutrophilia correlated with both urinary cortisol (R = 0.660, P = 0.007) and plasma creatine kinase (R = 0.523, P = 0.038) concentrations. These relationships were not observed in the CFS patients (R = 0.240, P = 0.370; R = 0.042, P = 0.892; and R = 0.293, P = 0.270; respectively). These results suggest that normal endocrine influences on the circulating neutrophil pool may be disrupted in patients with CFS.     

Influence of glucose ingestion by humans during recovery from exercise on substrate utilisation during subsequent exercise in a warm environment

Carbohydrate (CHO) ingestion during short-term recovery from prolonged running has been shown to increase the capacity for subsequent exercise in a warm environment. The aim of this study was to examine the effects of the amount of glucose given during recovery on substrate storage and utilisation during recovery and subsequent exercise in a warm environment. A group of 11 healthy male volunteers took part in two experiments in a controlled warm environment (35°C, 40% relative humidity), 1 week apart. On each occasion the subjects completed two treadmill runs (T1 and T2) at a speed equivalent to 60% of maximal oxygen uptake, for 90 min, until they were fatigued, or until aural temperature (T _aur) reached 39°C. The two runs were separated by a 4 h recovery period (REC), during which subjects consumed 55 g of naturally enriched [U-¹³C]-glucose in the form of a 7.5% carbohydrate-electrolyte solution (CES, mass of solution 667 g) immediately after T1. The subjects then consumed either: the same quantity of CES, or an equivalent volume of an electrolyte placebo, at 60, 120 and 180 min during REC, providing a total of 220 g (C220) or 55 g (C55) of [U-¹³C]-glucose, respectively. Expired gases were collected at 15 min intervals during exercise and 60 min intervals during REC, for determination of total CHO and fat oxidation by indirect respiratory calorimetry, and orally ingested [U-¹³C]-glucose oxidation, estimated from the ¹³C:¹²C ratio of expired CO₂. Substrate metabolism did not differ between conditions during T1. Despite the fact that total CHO (P<0.05) and ingested glucose oxidation (P<0.01) were greater during REC of the C220 condition, glycogen synthesis was estimated to be approximately fivefold greater (P<0.01) than in the C55 condition. During T2 the rate of total CHO oxidation was higher (P<0.01) and total fat oxidation lower (P<0.01) at all times during the C220 compared to the C55 condition. The greater CHO oxidation during C220 appeared to be met from ingested sources, as the rate of [U-¹³C]-glucose oxidation was greater (P<0.01) at all times during T2, compared to C55. Whilst more of the ingested substrate remained unoxidised on completion of T2 during C220, exercise duration was similar in the two experimental conditions, and was limited by thermoregulatory incapacity (T _aur>39°C) rather than substrate availability per se. Electronic Publication     

The effect of dietary carbohydrate intake on the metabolic response to prolonged walking on consecutive days

Summary Six healthy subjects walked 37 km per day for four consecutive days on two occasions one month apart; on one walk, subjects consumed a high carbohydrate (CHO) diet (85±1% CHO, Mean±SE) and on the other walk an isocaloric low CHO diet (2±0% CHO) was consumed. Subjects were fasted each day until after the completion of the walk. Blood samples were obtained at rest prior to exercise and after completion of each of three laps of 12.3 km. Exercise intensity corresponded to approximately 17% ofV _{O 2max}. The first day of each walk demonstrated that the pattern of substrate mobilisation in response to this type of exercise is highly reproducible, there being no difference in any of the parameters measured between the two walks. Circulating glucose, lactate, insulin and triglyceride levels remained essentially unchanged; alanine fell progressively and glycerol, free fatty acid (FFA) and 3-hydroxybutyrate (BHB) rose progressively. After the first day there was a general tendency for the blood glucose concentration to decline as exercise progressed; by the end of the walk on Day 2, blood glucose was lower on the low CHO diet than on the high CHO diet. On Day 4 plasma insulin was higher (p<0.05) on the high CHO diet than on the low CHO diet and declined progressively on both diets. Blood lactate and alanine concentrations were generally higher at rest on the high CHO diet, but fell so that no differences existed by the end of exercise. Glycerol, FFA and BHB levels rose progressively on the low CHO diet and were generally higher than on the high CHO diet where no increase was seen until the later stages of exercise. Plasma triglycerides were higher on the high CHO diet than on the low CHO diet. These results indicate that even in the overnight fasted state, substrate mobilisation during prolonged low intensity exercise is markedly influenced by the composition of the preceding diet. A high CHO diet results in suppression of lipid mobilisation, and hence utilisation, and this effect may be mediated in part by increased circulating insulin levels on the high CHO diet.     

Effects of acute carbohydrate supplementation during sessions of high-intensity intermittent exercise

Abs tract The present study evaluated the acute effects of carbohydrate supplementation on heart rate (HR), rate of perceived exertion (RPE), metabolic and hormonal responses during and after sessions of high-intensity intermittent running exercise. Fifteen endurance runners (26 ± 5 years, 64.5 ± 4.9 kg) performed two sessions of intermittent exercise under carbohydrate (CHO) and placebo (PLA) ingestion. The sessions consisted of 12 × 800 m separated by intervals of 1 min 30 s at a mean velocity corresponding to the previously performed 3-km time trial. Both the CHO and PLA sessions were concluded within ∼28 min. Blood glucose was significantly elevated in both sessions (123.9 ± 13.2 mg dl⁻¹ on CHO and 147.2 ± 16.3 mg dl⁻¹ on PLA) and mean blood lactate was significantly higher in the CHO (11.4 ± 4.9 mmol l⁻¹) than in the PLA condition (8.4 ± 5.1 mmol l⁻¹) (P < 0.05). The metabolic stress induced by the exercise model used was confirmed by the elevated HR (∼182 bpm) and RPE (∼18 on the 15-point Borg scale) for both conditions. No significant differences in plasma insulin, cortisol or free fatty acids were observed during exercise between the two trials. During the recovery period, free fatty acid and insulin concentrations were significantly lower in the CHO trial. Supplementation with CHO resulted in higher lactate associated with lipolytic suppression, but did not attenuate the cortisol, RPE or HR responses.     

Fluid replacement drinks during high intensity exercise effects on minimizing exercise-induced disturbances in homeostasis

Summary The purpose of these experiments was to examine the influence of various fluid replacement drinks on exercise-induced disturbances in homeostasis during heavy exercise. Nine trained cyclists performed constant load exercise on a cycle ergometer to fatigue on three occasions with 1-week separating experiments. The work rate was set initially at 85% of (range 82–88%) with fatigue being defined as a 10% decline in power output below the initial value. During each experiment subjects consumed one of the following three beverages prior to and every 15 min during exercise: (1) non-electrolyte placebo (NEP; 31 mosmol · kg^–1); (2) glucose polymer drink containing electrolytes (GP; 7% CHO, 231 mosmol · kg^–1), and (3) electrolyte placebo drink without carbohydrate (EP; 48 mosmol · kg^–1). Both the GP and EP beverage contained sodium citrate/citric acid (C) as a flavoring agent while C was not contained in the NEP drink. Although seven of nine subjects worked longer during the GP and EP treatment when compared with the NEP trial, the difference was not significant (P>0.05). No differences (P>0.05) existed between the GP and EP treatments in performance time. Exercise changes in rectal temperature, heart rate, % plasma volume and plasma concentrations of total protein, free fatty acids, glucose, lactate, potassium, chloride, calcium, and sodium did not differ (P>0.05) between trials. In contrast, blood hydrogen ion concentration [H⁺] was significantly lower (P<0.05) at 30 min of exercise during the GP and EP treatment when compared with the NEP run. These data provide evidence that electrolyte drinks do not minimize exercise-induced disturbances in blood-electrolyte concentrations during heavy execrcise when compared with nonelectrolyte drinks; however, these results suggest that fluid replacement beverages containing buffers (i.e. C) and/or electrolytes may minimize blood alterations in [H⁺] during intense exercise. Additional research is required to determine if the buffering influence of these beverages has an ergogenic benefit during heavy exercise.