Effects of pre-exercise ingestion of trehalose,galactose and glucose on subsequent metabolism and cycling performance

The glycaemic and insulinaemic responses to different carbohydrates vary and these have been suggested to affect performance. The purpose of the present study was to determine the effects of pre-exercise ingestion of glucose (GLU), galactose (GAL) and trehalose (TRE) on metabolic responses at rest and during exercise and on subsequent time-trial (TT) performance. Eight well-trained male cyclists completed three exercise trials separated by at least 3 days. At 45 min before the start of exercise subjects consumed 500 ml of a beverage containing 75 g of either glucose, galactose or trehalose. The exercise trials consisted of 20 min of submaximal steady-state exercise (SS) at 65% of maximal power output immediately followed by a [mean (SEM)] 702 (25) kJ TT. Plasma glucose concentration 15 min postprandial was significantly higher in GLU compared to GAL and TRE (P<0.05). This was accompanied by a more than twofold greater rise in plasma insulin concentration in GLU compared to GAL and TRE (118% and 145%, respectively). During SS exercise four subjects in GLU and one subject in TRE developed a rebound hypoglycaemia (plasma glucose concentration less than 3.5 mmol·l^–1). No differences were observed in TT performance between the three trials. Pre-exercise ingestion of trehalose and galactose resulted in lower plasma glucose and insulin responses prior to exercise and reduced the prevalence of rebound hypoglycaemia. Despite the attenuated insulin and glucose responses at rest and during exercise following pre-exercise ingestion of galactose and trehalose, there was no difference in TT performance compared with pre-exercise ingestion of glucose. Electronic Publication     

Comparison of the effects of pre-exercise feeding of glucose,glycerol and placebo on endurance and fuel homeostasis in man

Summary Six men were studied during exercise to exhaustion on a cycle ergometer at 73% of following ingestion of glycerol, glucose or placebo. Five of the subjects exercised for longer on the glucose trial compared to the placebo trial (p<0.1; 108.8 vs 95.9 min). Exercise time to exhaustion on the glucose trial was longer (p<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 · 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 · l^–1 during the exercise. The ingestion of glycerol (lg · 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<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. These data contrast with previous reports that have indicated glucose feeding pre-exercise produces hypoglycaemia during strenuous submaximal exercise and reduces endurance performance. It appears that man cannot use glycerol as a gluconeogenic substrate rapidly enough to serve as a major energy source during this type of exercise.     

Effects of pre-exercise ingestion of carbohydrate on glycaemic and insulinaemic responses during subsequent exercise at differing intensities

The development of rebound hypoglycaemia has been reported after pre-exercise carbohydrate (CHO) ingestion in some studies but not in others. Differences in the experimental design and factors such as the exercise intensity are likely to be responsible for the discrepancies between these studies. Exercise intensity might be a crucial factor since it affects both insulinaemia and glucose uptake. Therefore the aim of the present study was to compare the glycaemic and insulinaemic responses to exercise at different intensities after ingestion of a standardized pre-exercise CHO load. Eight moderately trained subjects consumed 75 g of glucose 45 min prior to 20 min of exercise at 40%, 65% or 80% maximal power output. Blood samples were collected before glucose ingestion, at 15 min intervals at rest and 5 min intervals during exercise. During exercise, measurements of heart rate and breath-by-breath analysis of expired gas were performed continuously. The trials were performed at [mean (SEM)] 55 (1), 77 (1) and 90 (1) percentages maximal oxygen uptake . At the onset of exercise, plasma glucose concentration returned to pre-ingestion levels, while the insulin concentration was more than three times higher than at rest [on average 57 (7) compared to 16 (1) μU·ml^–1). During exercise, plasma glucose concentrations decreased during the first 5 min of exercise and then stabilized in all trials at concentrations that would not be considered to be hypoglycaemic. There were no significant differences in glucose or insulin concentrations between the three trials during exercise. These data suggest that the glycaemic response to ingestion of 75 g of CHO 45 min pre-exercise is similar during exercise of different intensities. Electronic Publication     

Effect of prior ingestion of glucose or fructose on the performance of exercise of intermediate duration

The metabolic responses induced by the ingestion of a beverage containing glucose (G), fructose (F) or placebo (W) 30 min before exercise of high intensity and intermediate duration have been investigated; in these conditions the energy processes are mostly dependent on aerobic reactions. A group of 11 male recreational sportsmen ran on a treadmill, at an intensity corresponding to 82% of peak oxygen consumption, until exhaustion on three different occasions (after ingestion of a beverage containing 75 g of G, 75 g of F or W). Plasma glucose, insulin, and lactic acid concentrations were determined just prior to the ingestion of the beverages, 30 min afterwards and 10 and 30 min after completion of the exercise. The mean endurance time was 644 (SD 261) s after the ingestion of G, 611 (SD 227) s after the ingestion of F and 584 (SD 189) s after the ingestion of the W (P < 0.05 between G and W). No differences in the oxygen uptake, respiratory quotient or lactate concentrations between the three trials were observed. Both plasma glucose and insulin concentrations determined in samples obtained immediately before the onset of exercise were higher when G was ingested than when F (P < 0.05 andP < 0.05, respectively) or W (P < 0.001 and P < 0.005, respectively) were ingested. These findings would suggest that the ingestion of G prior to an effort of intermediate duration may improve physical performance.     

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.     

Effects of acute expansion of plasma volume on cardiovascular and thermal function during prolonged exercise

To investigate the hypothesis that an increase in plasma volume (PV) is obligatory in reducing the cardiovascular drift that is associated with prolonged exercise following training, a plasma expander (Macrodex) was used to acutely elevate PV. Eight untrained volunteers [maximal oxygen consumption; V˙O_{2 max} 45.2 (2.2)?ml?·?kg^?1?·?min^?1, mean (SE)] cycled for 2?h [at 46 (4)% V˙O_{2 max} ] in ambient conditions either with no PV expansion (CON) or following PV expansions of either 14% (LOW) or 21% (HIGH). During CON, heart rate (HR) increased (P<0.05) from 147 (2.4)?beats?·?min^?1 to 173 (3.6)?beats?·?min^?1 from 15 to 120?min of exercise. Both LOW and HIGH conditions depressed (P<0.05) HR, an effect that was manifested following 15?min of exercise. In contrast, stroke volume (SV) was elevated following PV expansion, with values (ml) of 89.6 (6.8), 97.8 (5.9) and 104 (4.6) noted by 15?min of exercise for CON, LOW and HIGH conditions, respectively. Acute PV expansion, regardless of magnitude, also resulted in elevations in cardiac output (Q˙ _c). These differences between conditions persisted throughout the exercise, as did the elevation in Q˙ _c that was noted with LOW and HIGH conditions. No difference between Q˙ _c, HR or SV was found between LOW and HIGH. In addition, neither LOW nor HIGH conditions altered the change in rectal temperature that was observed during exercise. These results demonstrate that, at least for moderate exercise performed in ambient conditions, PV expansion serves only to alter cardiac function (Q˙ _c, HR, SV) early in exercise, and not to attenuate the drift that occurs as the exercise is prolonged.     

Changes in lipid profile variables in response to submaximal and maximal exercise in trained cyclists

This study examined the effect of prolonged submaximal exercise followed by a self-paced maximal performance test on cholesterol (T-Chol), triglycerides (TG), and high-density lipoprotein cholesterol (HDLC). Nine trained male athletes cycled at 70% of maximal oxygen consumption for 60 min, followed by a selfpaced maximal ride for 10 min. Venous blood samples were obtained at rest, at 30 and 60 min during submaximal exercise, and immediately after the performance test. Lactic acid, haematocrit (Hct), haemoglobin (Hb), T-Chol and TG were measured in the blood, while plasma was assayed for HDL-C. Plasma volume changes in response to exercise were calculated from Hct and Hb values and all lipid measurements were corrected accordingly. In order to ascertain the repeatability of lipid responses to exercise, all subjects were re-tested under identical testing conditions and experimental protocols. When data obtained during the two exercise trials were analysed by two-way ANOVA no significant differences (P > 0.05) between tests were observed. Consequently the data obtained during the two testing trials were pooled and analysed by one-way ANOVA. Blood lactic acid increased non-significantly (P > 0.05) during the prolonged submaximal test, but rose markedly (P < 0.05) following the performance ride. Lipid variables ascertained at rest were within the normal range for healthy subjects. ANOVA showed that blood T-Chol and TG were unchanged (P > 0.05), whereas HDL-C rose significantly (P < 0.05) in response to exercise. Post hoc analyses indicated that the latter change was due to a significant rise in HDL-C after the performance ride. It is concluded that apparent favourable changes in lipid profile variables occur in response to prolonged submaximal exercise followed by maximal effort, and these changes showed a good level of agreement over the two testing occasions.     

Influence of ambient temperature on plasma ammonia and lactate accumulation during prolonged submaximal and self-paced running

This study examined the effects of heat stress on the accumulation of plasma ammonia, lactate, and urate during prolonged running. Nine highly trained endurance runners completed two running trials in a counterbalanced fashion in cool (15°C) and in hot (35°C) humid (60% relative humidity) conditions. Subjects ran on a motorised treadmill at 70% of peak treadmill running speed for 30 min (submaximal) followed by a self-paced 8-km performance run. Blood was drawn at pre-exercise, end-submaximal and end-performance run and analysed for plasma ammonia, lactate, and urate. Four subjects failed to complete the performance run in the heat and the performance times for the rest of the subjects was increased from 27.3 (0.6) min in cool conditions to 31.3 (1.2) min in hot conditions (P<0.05). The end-performance rectal temperature was 38.6 (0.1) and 39.2 (0.1)°C (P<0.05) in cool and hot conditions, respectively. Differences in plasma lactate at the end of submaximal running were not significant. However, at the end of performance runs lactate was 6.0 (0.9) mmol·l^–1 in cool and 3.1 (0.5) mmol·l^–1 in hot conditions, values that were significantly different (P<0.05). Plasma ammonia increased from pre-exercise to ≅59 μmol·l^–1 at the end-submaximal runs for both coditions and further at the end of performance runs to 108.5 (11) μmol·l^–1 (P<0.05) in hot but not in cool conditions. Plasma urate increased from pre-exercise to 311.2 (25.9) μmol·l^–1 at end-submaximal runs and to ≅320.4 μmol·l^–1 at end-performance runs in hot and cool environments. The findings that plasma urate accumulation was similar at the completion of running in both conditions, while ammonia was significantly augmented in hot conditions compared with cool, suggest that ammonia accumulation during heat stress exercise might be derived from sources other than purine catabolism. Electronic Publication     

Caffeine ingestion attenuates the VO(2) slow component during intense exercise

The purpose of this study was to analyze the effects of caffeine ingestion on the slow component of oxygen uptake (DeltaVO(2)) during high-intensity endurance exercise. Nine subjects (8 male and 1 female; age: 21 +/- 1 years; VO(2 max): 57.9 +/- 1.5 ml kg(-1) min(-1)) performed two 9-min tests on a treadmill at a running velocity eliciting 90% of their VO(2 max), 60 min after ingesting either a placebo capsule (PLAC) or a capsule containing a caffeine dose of 5 mg (kg body mass)(-1) [CAFF]. The mean values of DeltaVO(2) were significantly lower in CAFF than in PLAC (83 +/- 31 ml min(-1) vs. 167 +/- 26 ml min(-1), respectively; p < 0.05). These findings suggest that the ergogenic effect of caffeine in a high-intensity endurance exercise shown in previous research may be partly mediated by a possible attenuation of the VO(2) slow component.     

Blood glucose extraction as a mediator of perceived exertion during prolonged exercise

Summary The effect of blood glucose extraction on the perception of exertion was examined during prolonged arm exercise. Eight male subjects consumed in counterbalanced order a standard daily diet containing either (1) 75 g dihydroxyacetone and 25 g sodium pyruvate (DHAP) or (2) an isocaloric amount of placebo, to manipulate blood glucose extraction. Following each 7-day diet, subjects exercised to exhaustion at 60% of peak arm oxygen consumption. Ratings of perceived exertion (Borg, CR-10 scale) were obtained for the arms (RPE-A), legs (RPE-L), chest (RPE-C) and overall body (RPE-O) every 10 min of exercise. After 60 min of continuous exercise, blood samples were drawn from the radial artery and axillary vein. Ratings of perceived exertion did not differ between trials during the first 50 min of exercise. At the 60-min time point, perceived exertion was lower (P < 0.01) in the DHAP than placebo trials for the arms (RPE-A: 4.25 vs 5.50) and overall body (RPE-O: 3.25 vs 4.00). These differences persisted throughout exercise. RPE-L and RPE-C did not differ between trials. Whole-arm arterial-venous glucose difference was higher (P < 0.05) in the DHAP (1.00 mmol · 1^–1) than placebo (0.36 mmol·1^–1) trials, as was fractional extraction of glucose (22.5 vs 9.0%). Respiratory exchange ratio was the same between trials. Triceps muscle glycogen was (1) higher in the DHAP than placebo trial at pre-exercise (P < 0.05), (2) decreased during exercise and (3) did not differ between trials at exercise termination. Free fatty acids, glycerol, -hydroxybutyrate, lactic acid, pH, norepinephrine and epinephrine did not differ between trials. These findings suggest that blood glucose extraction mediates the perceived intensity of exertion arising from active limbs during prolonged arm exercise.     

The Effects of Caffeine on the Kinetics of O2Uptake, CO2Production and Expiratory Ventilation in Humans During the On-Transient of Moderate and Heavy Intensity Exercise

In order to test the hypothesis that glycogen sparing observed early during exercise following caffeine ingestion was a consequence of tighter metabolic control reflected in faster VO2 kinetics, we examined the effect of caffeine ingestion on oxygen uptake (VO2), carbon dioxide production (VCO2) and expiratory ventilation (VE) kinetics at the onset of both moderate (MOD) and heavy (HVY) intensity exercise. Male subjects (n = 10) were assigned to either a MOD (50% VO2,max, n = 5) or HVY (80% VO2,max, n = 5) exercise condition. Constant-load cycle ergometer exercise was performed as a step function from loadless cycling 1 h after ingestion of either dextrose (placebo, PLAC) or caffeine (CAFF; 6 mg (kg body mass)-1). Alveolar gas exchange was measured breath-by-breath. A 2- or 3-component exponential model, fitted through the entire exercise transient, was used to analyse gas exchange and ventilatory data for the determination of total lag time (TLT: the time taken to attain 63% of the total exponential increase). Caffeine had no effect on TLT for VO2 kinetics at either exercise intensity (MOD: 36 +/- 14 s (PLAC) and 41 +/- 10 s (CAFF); HVY: 99 +/- 30 s (PLAC) and 103 +/- 26 (CAFF) (mean +/- S.D.)). TLT for VE was increased with caffeine at both exercise intensities (MOD: 50 +/- 20 s (PLAC) and 59 +/- 21 s (CAFF); HVY: 168 +/- 35 s (PLAC) and 203 +/- 48 s (CAFF)) and for VCO2 during MOD only (MOD: 47 +/- 14 s (PLAC) and 53 +/- 17 s (CAFF); HVY: 65 +/- 13 s (PLAC) and 69 +/- 17 s (CAFF)). Contrary to our hypothesis, the metabolic effects of caffeine did not alter the on-transient VO2 kinetics in moderate or heavy exercise. VCO2 kinetics were slowed by a reduction in CO2 stores reflected in pre-exercise and exercise endtidal CO2 pressure (PET,CO2) and plasma PCO2 which, we propose, contributed to slowed VE kinetics.     

Dehydration in soldiers during walking/running exercise in the heat and the effects of fluid ingestion during and after exercise

The aim of this study was to examine whether ingesting water alone, or dextrose (7.5?g?·?100?ml^?1) with electrolytes, or fructose/corn solids (7.5?g?·?100?ml^?1) (400?ml every 20?min) would reduce the perceived exertion associated with 16?km (3?h) walking/running in the heat compared with that perceived during exercise with no fluid intake. Perceived exertion was assessed at 1-h intervals during exercise. Blood samples, required for analysis of blood glucose, plasma sodium, plasma osmolality and plasma volume, were obtained prior to exercise and at 1-h intervals during the exercise; further samples were obtained 1-h intervals for 3?h following the exercise. Drinking fluids at regular intervals reduced the level of perceived exertion. In the test during which no fluid was ingested, body mass decreased by 4.9 (0.4)?kg [mean (SEM)], but decreased less with ingestion of either the dextrose/electrolytes or fructose/corn solids solutions, or water alone [1.3 (0.2)?kg, 1.6 (0.3)?kg and 2.0 (0.1)?kg, respectively]. Plasma volume fell by 17% when taking no fluid, but fell less when ingesting fluids. Blood glucose fell significantly (P<0.01) when taking no fluid and rose to 8.4 (1.3)?mmol?·?l^?1 (P<0.001) and 6.8 (1.1) mmol?·?l^?1 (P<0.01) with ingestion of the dextrose/electrolytes or fructose/corn solids solutions, respectively. Urine output was greater with ingestion of water than with any of the other drinks. Six subjects experienced fatigue during exercise with no fluid and failed to complete the exercise. These results suggest that fatigue was caused by several interacting factors: a fall in blood glucose and plasma volume, dehydration, and neuroglycopenia. Taking fluids during exercise reduced the strain and the rating of perceived exertion; this was better achieved by ingesting a dextrose/electrolytes solution.     

Oxidation of [13C]glucose ingested before and/or during prolonged exercise

Ingestion of glucose before exercise results in a transient increase in plasma insulin concentrations. We hypothesized that if glucose was also ingested during the exercise period the elevated plasma insulin concentration could increase exogenous glucose oxidation. The oxidation rate of glucose ingested 30 min before (50 g) and/or during (110 or 160 g in fractionated doses) exercise [120 min; 67.3 (1.2)% maximal O₂ uptake] was studied on six young male subjects, using ¹³C-labelling. Ingestion of glucose before exercise significantly increased plasma insulin concentration [from 196 (45) to 415 (57) pmol l^–1] but the value returned to pre-exercise level within the first 30 min of exercise in spite of a continuous increase in plasma glucose concentration. Ingestion of glucose 30 min before exercise did not increase the oxidation of exogenous glucose between minutes 30 and 60 during the exercise period [0.36 (0.03) vs 0.30 (0.02) g min^–1, when placebo or unlabelled glucose was ingested respectively]. Over the last 90 min of exercise, when glucose was ingested only during exercise, 49.2 (3.1) g [0.55 (0.04) g min^–1) was oxidized, while when it was ingested both before and during exercise, 65.7 (4.6) g [0.73 (0.05) g min^–1] was oxidized [26.7 (2.1) g of the 50 g ingested before exercise but only 39.0 (2.4) g of the 110 g ingested during the exercise period]. Thus, ingestion of glucose 30 min before the beginning of exercise did not enhance the oxidation rate of exogenous glucose ingested during the exercise period, although the total amount of exogenous glucose oxidized was larger than when ingested only during the exercise period.     

Thermoregulatory responses to ice-slush beverage ingestion and exercise in the heat

We compared the effects of an ice-slush beverage (ISB) and a cool liquid beverage (CLB) on cycling performance, changes in rectal temperature (T _re) and stress responses in hot, humid conditions. Ten trained male cyclists/triathletes completed two exercise trials (75 min cycling at ~60% peak power output + 50 min seated recovery + 75% peak power output × 30 min performance trial) on separate occasions in 34°C, 60% relative humidity. During the recovery phase before the performance trial, the athletes consumed either the ISB (mean ± SD −0.8 ± 0.1°C) or the CLB (18.4 ± 0.5°C). Performance time was not significantly different after consuming the ISB compared with the CLB (29.42 ± 2.07 min for ISB vs. 29.98 ± 3.07 min for CLB, P = 0.263). T _re (37.0 ± 0.3°C for ISB vs. 37.4 ± 0.2°C for CLB, P = 0.001) and physiological strain index (0.2 ± 0.6 for ISB vs. 1.1 ± 0.9 for CLB, P = 0.009) were lower at the end of recovery and before the performance trial after ingestion of the ISB compared with the CLB. Mean thermal sensation was lower (P < 0.001) during recovery with the ISB compared with the CLB. Changes in plasma volume and the concentrations of blood variables (i.e., glucose, lactate, electrolytes, cortisol and catecholamines) were similar between the two trials. In conclusion, ingestion of ISB did not significantly alter exercise performance even though it significantly reduced pre-exercise T _re compared with CLB. Irrespective of exercise performance outcomes, ingestion of ISB during recovery from exercise in hot humid environments is a practical and effective method for cooling athletes following exercise in hot environments.     

Effects of load and training modes on physiological and metabolic responses in resistance exercise

The aim of the study was to examine the effects of three different loads (LOAD) in combination with four different exercise modes (MODE) on physiological responses during and after one fatiguing bout of bench press exercise. Ten resistance-trained healthy male subjects performed bench press exercise each at 55% (LOW), 70% (MID) and 85% (HIGH) of 1 repetition maximum (1RM) for as many repetitions as possible and in four training modes: 4-1-4-1 (4-s concentric, 1-s isometric, 4-s eccentric and 1-s isometric successive actions), 2-1-2-1, 1-1-1-1 and MAX (maximum velocity concentric). Oxygen uptake [Formula: see text] was measured during exercise and for 30-min post-exercise. Maximum blood lactate concentration (blood LA(max)) and heart rate (HR(max)) were also determined. Number of repetitions (REPS) and exercise time (EXTIME) were recorded and accumulated lifted mass (MASS), defined by REPS × lifted mass, was calculated. LOAD had a significant effect on REPS (LOW > MID > HIGH, p < 0.01). A significant increase of REPS was obtained exercising at a faster MODE except from 1-1-1-1 to MAX (p < 0.01). EXTIME significantly decreased with increasing LOAD (LOW > MID > HIGH, p < 0.01 for all) and faster MODE (4-1-4-1, 2-1-2-1, 1-1-1-1 > MAX; p > 0.01). MASS decreased significantly with increasing LOAD (p < 0.01) but increased with a faster MODE (p < 0.05) with the exception of 1-1-1-1 to MAX. MODE had a significant effect on VO(2) (4-1-4-1 > MAX; p < 0.05). LOAD had a significant effect on consumed O(2) during exercise (LOW > MID and HIGH; p > 0.01) and on blood LA(max) (LOW and MID > HIGH; p < 0.01). The data indicate that physiological responses on different resistance exercises depend on both the load and the velocity mode.     

Effects of supramaximal exercise on blood glucose levels during a subsequent exercise

Summary The purpose of the present investigation was to examine the effects of hyperglycoemia induced by supramaximal exercise on blood glucose homeostasis during submaximal exercise following immediately after. Six men were subjected to three experimental situations; in two of these situations, 3 min of high-intensity exercise (corresponding to 112, SD 1%VO_{2 max}) was immediately followed by either a 60-min period of submaximal exercise (68, SD 2%VO_{2 max}) or a 60-min resting period. In the third situation, subjects performed a 63-min period of submaximal exercise only. There were no significant differences between the heurt rates, oxygen uptakes, and respiratory exchange ratios during the two submaximal exercise bouts (> 15 min) whether or not preceded by supramaximal exercise. The supramaximal exercise was associated within 10 min of the start increases (P<0.05) in blood glucose, insulin, and lactate concentrations. This hyperglycemia was more pronounced when subjects continued to exercise submaximally than when they rested (at 7.5 min;P<0.05). There was a more rapid return to normal exercise blood glucose and insulin values during submaximal exercise compared with rest. The data show that the hyperinsulinemia following supramaximal exercise is corrected in between 10–30 min during submaximal exercise following immediately, suggesting that this exercise combination does not lead to premature hypoglycemia.     

Acute dopamine/noradrenaline reuptake inhibition enhances human exercise performance in warm, but not temperate conditions

Nine healthy endurance-trained males were recruited to examine the effect of a dual dopamine/noradrenaline reuptake inhibitor on performance, thermoregulation and the hormonal responses to exercise. Subjects performed four trials, ingesting either a placebo (pla) or 2 × 300 mg bupropion (bup), prior to exercise in temperate (18°C) or warm (30°C) conditions. Trials consisted of 60 min cycle exercise at 55% W _max immediately followed by a time trial (TT). TT performance in the heat was significantly improved by bupropion (pla: 39.8 ± 3.9 min, bup: 36.4 ± 5.7 min; P = 0.046), but no difference between treatments was apparent in temperate conditions (pla: 30.6 ± 2.2 min, bup: 30.6 ± 1.9 min; P = 0.954). While TT power output was consistently lower in the heat when compared to temperate conditions, this decrement was attenuated by bupropion. At the end of the TT in the heat, both core temperature (pla 39.7 ± 0.3°C, bup 40.0 ± 0.3°C; P = 0.017) and HR (pla 178 ± 7 beats min⁻¹, bup 183 ± 12 beats min⁻¹; P = 0.039), were higher in the bupropion trial than in the placebo. Circulating pituitary and adrenal hormone concentrations increased throughout exercise in all trials. Circulating serum prolactin was elevated above temperate levels during exercise in a warm environment ( P < 0.001). These data indicate that performance in warm conditions is enhanced by acute administration of a dual dopamine/noradrenaline reuptake inhibitor. No such effect was apparent under temperate conditions. It appears that bupropion enabled subjects to maintain a greater TT power output in the heat with the same perception of effort and thermal stress reported during the placebo trial, despite the attainment of a higher core temperature.     

Performance and thermoregulatory effects of chronic bupropion administration in the heat

The combination of acute dopamine/noradrenaline reuptake inhibition (bupropion; BUP) and heat stress (30°C) significantly improves performance (9%). Furthermore the maintenance of a higher power output resulted in the attainment of significantly higher heart rates and rectal temperatures—above 40°C—in the BUP trial compared to the placebo trial. Since BUP is an aid to cease smoking that is taken for longer periods, question remains if similar performance and thermoregulatory effects are found following administration of BUP over several days (10 days). The purpose of the present study was to examine the effects of chronic BUP on exercise performance, thermoregulation and hormonal variables in the heat. Eight trained male cyclists participated in the study. Subjects completed two trials consisting of 60 min fixed intensity exercise (55% W _max) followed by a time trial (TT) in a double-blind randomized crossover design. Exercise was performed in 30°C. Subjects took either placebo (PLAC) or BUP (Zyban™) for 3 days (150 mg), followed by 300 mg for 7 days. Chronic BUP did not influence TT performance (BUP 40′42″ ± 4′18″; PLAC 41′36″ ± 5′12″), but significantly increased core temperature (P = 0.030). BUP significantly increased circulating growth hormone levels (PLAC: 9.8 ± 5.8 ng L⁻¹; BUP: 13 ± 6.8 ng L⁻¹; P < 0.008). Discussion/conclusion: Chronic BUP did not influence TT performance in 30°C and subjects did not reach core temperature values as high as observed during the acute BUP study. It seems that chronic administration results in an adaptation of central neurotransmitter homeostasis, resulting in a different response to the drug.     

Effect of caffeine ingestion on lymphocyte counts and subset activation in vivo following strenuous cycling

Caffeine ingestion is associated with increases in the concentration of plasma epinephrine and epinephrine is associated with alterations in immune cell trafficking and function following intensive exercise. Therefore, the purpose of this study was to investigate the effect of caffeine ingestion on plasma epinephrine concentration, lymphocyte counts and subset activation in vivo, as measured by the expression the CD69 surface antigen, before and after intensive cycling. On two occasions, following an overnight fast and 60 h abstention from caffeine containing foods and drinks, eight endurance trained males cycled for 90 min at 70% O_{2 max} 60 min after ingesting caffeine (6 mg kg^–1 body mass; CAF) or placebo (PLA). Venous blood samples were collected at pre-treatment, pre-exercise, post-exercise and 1 h post-exercise. Plasma epinephrine concentrations were significantly higher in CAF compared with PLA at pre-exercise [0.28 (0.05) nmol l^–1 versus 0.08 (0.03) nmol l^–1, P<0.01; mean (SE)] and immediately post-exercise [1.02 (0.16) nmol l^–1 versuss 0.60 (0.13) nmol l^–1, P<0.01]. Compared with pre-treatment, numbers of CD4⁺ and CD8⁺ cells decreased by 54% and 55%, respectively, in CAF at 1 h post-exercise (both P<0.01) but did not significantly differ in PLA. Compared with PLA, in CAF the percentage of CD4⁺CD69⁺ cells was 5-fold higher at post-exercise (P<0.05) and 5.5-fold higher at 1 h post-exercise (P=0.01). Compared with PLA, in CAF the percentage of CD8⁺CD69⁺ cells was 2-fold higher at pre-exercise (P<0.05) and 1.7-fold higher at post-exercise (P<0.05). These findings suggest that caffeine ingestion is associated with alterations in lymphocyte subset trafficking and expression of CD69 in vivo following prolonged, intensive exercise.     

Single and choice reaction time during prolonged exercise in trained subjects: influence of carbohydrate availability

The aim of the present study was to examine the effects of prolonged exercise at the ventilatory threshold and carbohydrate ingestion on single (SRT) and choice (CRT) reaction time. Eight well-trained triathletes completed three testing sessions within a 3-week period. Maximal oxygen uptake was determined in the first test, whereas the second and the third sessions were composed of a 100-min run (treadmill 15 min, overground 70 min, treadmill 15 min) performed at the velocity associated with the ventilatory threshold. During these submaximal tests, the subjects ingested (in random order) 8 ml·kg^–1 body weight of either a placebo (Pl) or 5.5% carbohydrate (CHO) solution prior to the first submaximal run and 2 ml·kg^–1 body weight every 15 min after that. The cognitive tasks were performed before and after exercise for CRT, and before, during each submaximal run and after exercise for SRT. Furthermore, at the end of each submaximal test subjects were asked to report their rating of perceived exertion (RPE). Results showed a significant positive effect of CHO ingestion on RPE and CRT performance at the end of exercise, while no effect of exercise duration was found in the Pl condition. After a 100-min run, during the CHO condition, CRT mean (SD) group values decreased from 688.5 (51) ms to 654 (63) ms, while during the Pl condition, RPE mean group values increased from 11 (2) to 16 (1.02) and CRT mean values remained stable [688 (104) ms vs 676 (73.4) ms, P>0.05]. No similar effect was observed for SRT. These results suggest that CHO-electrolyte ingestion during a100-min run results in an improvement in the complex cognitive performance measured at the end of that run. Electronic Publication