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.     

Plasma glucagon and catecholamines during exhaustive short-term exercise

Summary Plasma glucagon and catecholamine levels were measured in male athletes before and after exhaustive 15 min continuous running and strenuous intermittent short-term exercise (3×300 m). Blood lactate levels were higher after the intermittent exercise (mean 16.7 mmol×l^–1) than after the continuous running (mean 7.1 mmol×l^–1). Plasma glucagon concentration increased during continuous running and intermittent exercise by 41% and 55%, respectively, and the increases in plasma noradrenaline concentration were 7.7- and 9.1-fold compared with the respective pre-exercise values. Immediately after the exercises plasma cyclic AMP, blood glucose and alanine levels were elevated significantly.The data suggest that the sympathoadrenal system is of major importance for liver glucose production during high-intensity exercises. Catecholamines directly stimulate liver glucose production and may indirectly stimulate it by enhancing the secretion of glucagon.     

Relationship between plasma ammonia and blood lactate concentrations after maximal treadmill exercise in circumpubertal girls and boys

Summary The purpose of the study was to define a relationship between plasma ammonia [NH₃]_p1 and blood lactate concentrations [1a^–]_b after exercise in children and to find out whether the [NH₃]_p1, determined during laboratory treadmill tests, may be useful as a predictor of the children's sprint running ability. A group of 20 girls and 14 boys trained in athletics or swimming and 8 untrained boys, aged 13.2 to 13.7 years, participated in the study. Their [NH₃]_p1 and [1a^–]_b were measured before and after incremental maximal treadmill exercise. In addition, the subjects' running performance was tested in 30-, 60- and 600- or 1000-m runs under field conditions. The [NH₃]_p1 during the treadmill runs increased by 20.1 (SD 17.3), 24 (SD 16.7) and 10 (SD 4.3) mol·1^–1 in the girls, the trained boys and the untrained boys, respectively. The postexercise [NH₃]_p1 correlated positively with [1a^–]_b (r=0.565 in the girls and 0.812 in the boys) and treadmill speed attained during the test (r=0.489 in the girls and 0.490 in the boys). Significant correlations were also found between [NH₃]_p1 obtained during the treadmill test and the times of 30- and 60-m runs (r= –0.676 and –0.648, respectively) in the boys but not in the girls. A comparison of the present data with those reported previously in adults showed that increases in [NH₃]_p1 during maximal exercise in children would seem to be lower than in adult subjects both in absolute values and in relation to [1a^–]_b. The present data would also suggest that [NH₃]_p1 reflects involvement of anaerobic processes during maximal treadmill exercise in circumpubertal children but it has a small practical value for predictiton of their sprint running ability.     

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     

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     

Catecholamines,lymphocyte subsets,and cyclic adenosine monophosphate production in mononuclear cells and CD4+ cells in response to submaximal resistance exercise

We examined the effect of 30 min of submaximal resistance exercise on free and sulphoconjugated plasma catecholamine concentrations determined by high performance (-pressure) liquid chromatography separation, the distribution of circulating lymphocytes quantified by flow cytometry, and isoproterenol induced cyclic adenosine monophosphate (cAMP) production in mononuclear cells (MNL) and CD4⁺ cells. Venous blood samples were taken before, immediately after and 45 min after exercise. Resistance exercise increased free plasma adrenaline (A) and noradrenaline (NA) concentrations, whereas sulphoconjugated catecholamine concentrations remained unchanged. Exercise induced leucocytosis and lymphocytosis was predominantly manifested by an increase in the number of total lymphocytes, monocytes, CD3⁺, CD8⁺ cells and CD3^– CD16/CD56^– cells. Redistribution resulted in a decrease in the CD4^–: CD8⁺ ratio. The total number and distribution of lymphocytes returned to baseline after 45-min rest. An exercise-induced increase in the number of CD3^– CD16/CD56⁺ cells was significantly correlated with the increase in plasma NA (r = 0.66;P = 0.035), indicating a NA dependent process of redistribution. The cAMP-production in MNL was significantly elevated after resistance exercise, when cells were stimulated with 1 mol·1^–1 isoproterenol [pre-exercise 16.5 (SD 3.3); postexercise 21.6 (SD 9.8); 45 min postexercise 10.7 (SD 2.8)]. The cAMP production in CD4⁺ cells was not affected by exercise. Therefore, it is discussed whether redistribution is responsible for the exercise induced increase in cAMP production in MNL.     

Glucocorticoid response to exercise as measured by serum and salivary cortisol

Summary Serum and salivary cortisol concentrations were studied in 78 elite athletes engaged in different sports, by subjecting them to high-intensity laboratory exercise. The mean difference in the pre-exercise cortisol concentrations in the seven groups studied were more marked in serum (from 311 to 768 nmol · l^–1) than in saliva (from 17.9 to 22.7 nmol · 1^–1, only one group reaching 40 nmol ·^–1). Judging from the correlation coefficients based on total variances, the post-/pre-exercise differences in cortisol concentrations in serum depended chiefly on pre-exercise values, while those in saliva tended to depend more on the postexercise concentrations. The coefficients of correlation between that difference and either the pre- or postexercise values were –0.71 and 0.47, respectively, for serum, and –0.51 and 0.58, respectively, for saliva. This would suggest that salivary cortisol concentration might be a more suitable variable for assessing glucocorticoid activity in exercise than serum cortisol concentration, probably being less sensitive to pre-exercise emotional state.     

Plasma glucose,insulin and catecholamine responses to a Wingate test in physically active women and men

The influence of gender on the glucose response to exercise remains contradictory. Moreover, to our knowledge, the glucoregulatory responses to anaerobic sprint exercise have only been studied in male subjects. Hence, the aim of the present study was to compare glucoregulatory metabolic (glucose and lactate) and hormonal (insulin, catecholamines and estradiol only in women) responses to a 30-s Wingate test, in physically active students. Eight women [19.8 (0.7) years] and eight men [22.0 (0.6) years] participated in a 30-s Wingate test on a bicycle ergometer. Plasma glucose, insulin, and catecholamine concentrations were determined at rest, at the end of both the warm-up and the exercise period and during the recovery (5, 10, 20, and 30 min). Results showed that the plasma glucose increase in response to a 30-s Wingate test was significantly higher in women than in men [0.99 (0.15) versus 0.33 (0.20) mmol l^–1 respectively, P<0.05]. Plasma insulin concentrations peaked at 10 min post-exercise and the increase between this time of recovery and the end of the warm-up was also significantly higher in women than in men [14.7 (2.9) versus 2.3 (1.9) pmol l^–1 respectively, P<0.05]. However, there was no gender difference concerning the catecholamine response. The study indicates a gender-related difference in post-exercise plasma glucose and insulin responses after a supramaximal exercise.     

Cardiopulmonary adjustment and metabolic response to maximal and submaximal physical exercise of boys and girls at different stages of maturity

Summary Cardiopulmonary and metabolic variables were investigated at maximal and submaximal bicycle ergometer exercises in 41 swimmers of both sexes, 8–18 years old. O₂ max and O₂ max·HR^–1 were higher in boys than in girls and increased with maturity, while O₂ max·kg^–1 and HVE were not influenced by this. The HV increased clearly during this growth period, the pubertal and postpubertal subjects showing 16 and 17% higher values for HV and HV·kg^–1 than those reported in normal schoolchildren populations. During the submaximal exercise at 70% O₂ max the highest HR values were found in the prepubertal group, whilst the lowest were observed in the postpubertal subjects. These findings suggest that a given percentage of O₂ max as a reference unit, is more reliable than a certain HR to obtain comparable results in subjects with different ages.Blood samples were collected before, during, and after the submaximal exercise. Blood glucose and FFA did not differ in relation to the stages of maturity. During exercise, insulin decreased in prepubertal children, did not alter in pubertal adolescents, and increased in postpubertal subjects. The lactate concentration, during exercise, increased in relation to maturity. The same results were found for HGH, but no differences were found with regard to sex. Since the pattern of HGH secretion during exercise is similar to that found after arginine and insulin administration it is assumed that the same mechanism (i.e., sex hormones) triggers the HGH release.Abbreviations HV heart volume - HV·kg^–1 heart volume per kg body weight - HR heart rate - average heart rate during the submaximal exercise - WL work load - W·kg^–1 watts per kg body weight - O₂ max maximal oxygen consumption - 70% O₂ max 70% of maximal oxygen consumption - O₂ max·HR^–1 oxygen pulse - HVE heart volume equivalent (HV/ O₂ max·HR^–1) - FFA free fatty acids - HGH human growth hormone     

Threshold increases in plasma growth hormone in relation to plasma catecholamine and blood lactate concentrations during progressive exercise in endurance-trained athletes

Plasma human growth hormone ([HGH]), adrenaline ([A]), noradrenaline ([NA]) and blood lactate ([La^–]_b) concentrations were measured during progressive, multistage exercise on a cycle ergometer in 12 endurance-trained athletes [aged 32.0 (SEM 2.0) years]. Exercise intensities (3 min each) were increased by 50 W until the subjects felt exhausted. Venous blood samples were taken after each intensity. The [HGH] and catecholamine concentrations increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to the lactate threshold ([La^–]-T). Close correlations (P < 0.001) were found between [La^–]_b and plasma [HGH] (r = 0.64), [A] (r = 0.71) and [NA] (r = 0.81). The mean threshold exercise intensities for [HGH], [A] and [NA], detected by log-log transformation, [154 (SEM 19) W, 162 (SEM 15) W and 160 (SEM 17) W, respectively] were not significantly different from the [La^–]-T [161 (SEM 12) W]. The results indicated that the threshold rise in plasma [HGH] followed the patterns of plasma catecholamine and blood lactate accumulation during progressive exercise in the endurancetrained athletes.     

Effects of dietary manipulations on blood glucose and hormonal responses following supramaximal exercise

Summary The effects of supramaximal exercise on blood glucose, insulin, and catecholamine responses were examined in 7 healthy male physical education students (mean±SD: age=21±1.2 years; =54±6 ml · kg^–1 · min^–1) in response to the following three dietary conditions: 1) a normal mixed diet (N); 2) a 24-h low carbohydrate (CHO) diet intended to reduce liver glycogen content (D₁); and 3) a 24-h low CHO diet preceded by a leg muscle CHO overloading protocol intended to reduce hepatic glycogen content with increased muscle glycogen store (D₂). Exercise was performed on a bicycle ergometer at an exercise intensity of 130% for 90 s. Irrespective of the dietary manipulation, supramaximal exercise was associated with a similar significant (p<0.01) increase in the exercise and recovery plasma glucose values. The increase in blood glucose levels was accompanied by a similar increase in insulin concentrations in all three groups despite lower resting insulin levels in conditions D₁ and D₂. Lactate concentrations were higher during the early phase of the recovery period in the D₂ as compared to the N condition. At cessation of exercise, epinephrine and norepinephrine were greatly elevated in all three conditions. These results indicate that the increase in plasma glucose and insulin associated with very high intensity exercise, persists in spite of dietary manipulations intended to reduce liver glycogen content or increase muscle glycogen store. These data suggest that the blood glucose increase following supramaximal exercise is most likely related to hepatic glycogenolysis in spite of a substantial decrease in liver glycogen content.     

The peak oxygen uptake of British children with reference to age,sex and sexual maturity

Summary The purposes of this study were to provide baseline data on the peak oxygen consumption (VO₂) of British children, aged 11–16 years and to examine the peakVO₂ of children in relation to their pubertal stage of development. The peakVO₂ of 226 boys and 194 girls was determined during either treadmill running or cycle ergometry. The sexual maturity of 320 of the children was estimated using Tanner's indices. PeakVO₂ increased with chronological age in both sexes and from about the age of 12 years boys exhibited significantly higher (P<0.05) values than girls. Boys' peakVO₂ in relation to body mass was consistent over the age range studied and was superior (P<0.05) to girls' values at all ages. It appears that mass-related peakVO₂ is independent of sexual maturity in both sexes. The more mature boys demonstrated a significantly higher (P<0.05) peakVO₂ (l·min^–1) than the less mature boys on both ergometers. The more mature girls demonstrated significantly higher (P<0.05) peakVO₂ (l·min^–1) than the less mature girls only on the cycle ergometer. On both ergometers the differences between the peakVO₂ of the girls and boys were more pronounced in the mature children whether expressed in relation to body mass or not. Comparison of the results with earlier data drawn from smaller samples failed to provide evidence to suggest that British children's peakVO₂ has declined in recent years. No study with which to compare our maturity peakVO₂ data appears to be available.     

Effect of the intensity of training on catecholamine responses to supramaximal exercise in endurance-trained men

In this study we investigated whether plasma catecholamine responses to the Wingate test are affected by the intensity of training in endurance-trained subjects. To do this we compared plasma adrenaline (A) and noradrenaline (NA) concentrations in response to a Wingate test in three different groups: specialist middle-distance runners (MDR) in 800-m and 1,500-m races, specialist long-distance runners (LDR) 5,000-m and 10,000-m races, and untrained subjects (UT). The maximal power (W _max) and the mean power (W) were determined from the Wingate test. Blood lactate (La), plasma A and NA concentrations were analysed at rest (La₀, A₀ and NA₀), immediately at the end of the exercise (A_max and NA_max) and after 5 min recovery (La_max, A₅ and NA₅). The ratio A_max/NA_max was considered as an index of the adrenal medulla responsiveness to the sympathetic nervous activity. At the end of the test, W _max and W were similar in the three groups but La_max was significantly greater in MDR compared to LDR and UT [15.2 (2.2) mmol l^–1, 11.7 (3.1) mmol l^–1, 11.6 (1.6) mmol l^–1, respectively, for MDR, LDR and UT; mean (SD)]. Concerning the plasma catecholamine concentrations in response to exercise, MDR and LDR A_max values [3.73 (1.53) nmol l^–1, 3.47 (0.74) nmol l^–1, respectively, for MDR and LDR] were significantly greater than those of UT [1.48 (0.32) nmol l^–1] who also exhibited the lowest NA_max values [11.09 (6.58) nmol l^–1] compared to MDR and LDR [20.43 (3.51) nmol l^–1; 15.85 (4.88) nmol l^–1, respectively, for MDR and LDR]. However, no significant differences were observed between the two trained groups either for A_max or NA_max. These results suggest that long-term endurance training can enhance plasma catecholamine concentrations in response to supramaximal exercise. However, as there were no significant differences between MDR and LDR A_max and NA_max values, the effect of the intensity of training remains to be clarified.     

Haematological and acute-phase responses associated with delayed-onset muscle soreness in humans

Delayed-onset muscle soreness following unaccustomed or eccentric exercise is associated with inflammation, tissue necrosis and the release of muscle enzymes (Newham et al. 1983). We have investigated the time course of changes in circulating leucocytes and serum levels of some acute phase reactants, serum creatine kinase activity (CK) and muscle pain after a 40-min bout of bench-stepping exercise in eight healthy untrained subjects. Leg muscle soreness was greatest 2 days after the exercise bout. Peak serum CK values [mean (SD) 540 (502) IU·l^–1] occurred 1–7 days post-exercise. Serum C-reactive protein (CRP) was unchanged from pre-exercise levels [7.8 (3.4) mg·l^–1] immediately post-exercise [7.9 (2.3) mg·l^–1] but rose to a peak of 17.0 (3.9) mg·l^–1 1 day post-exercise, thereafter declining to basal levels. Serum levels of iron and zinc fell below pre-exercise levels for 1–3 days post-exercise. Serum albumin, IgG and IgM fell below pre-exercise levels from 1 day post-exercise, reaching minimal values (about 80% of basal levels) at 7 days post-exercise. The exercise did not appear to significantly affect serum levels of alpha-1-antitrypsin and alpha-1-acid glycoprotein. Two and three days after the exercise bout the circulating numbers of total leucocytes, neutrophils, monocytes and basophils fell 15–20% below pre-exercise levels, whereas lymphocytes, eosinophils and platelets were unchanged. The results indicate that a rapid acute phase inflammatory response is initiated within 1 day of a bout of exercise that induces delayed-onset muscle soreness, and that any later tissue necrosis that may occur is not accompanied by further marked changes in acute-phase reactants such as CRP.     

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.     

Maximal O2 uptake of boys and girls — ages 14–17

Summary White high school girls (n = 120) and boys (n = 120) aged 14–17 years, selected from 9th, 10th, 11th and 12 grades of a northern, midwest U.S. high school performed running exercise on a motor driven treadmill for determinations of maximal O₂ uptake ( O₂ max).The mean O₂ max for all age groups was 40.8±4.0 and 54.7±5.6 ml/kg·min^–1 for girls and boys respectively. The difference in O₂ max across age groups varied only from 40.2–41.2 ml/kg·min^–1 for girls and 54.0–56.3 ml/kg·min^–1 for boys. These differences were not significant (P>0.05). The reported O₂ max data are compared with those reported in other studies for bicycle ergometer and treadmill exercise using similar age groups.     

Sustained noradrenaline sulphate response in long-distance runners and untrained subjects up to 2 h after exhausting exercise

Summary We investigated the response of plasma and platelet free catecholamine ([CA]) and sulphated catecholamine ([CA-S]) concentrations after an incremental treadmill test to exhaustion and during recovery. In triathletes (n = 9) plasma and platelet [CA] and [CA-S] were measured before, immediately after and 0.5 and 24 h after exercise. In long-distance runners (n = 9) and in controls (n = 10) plasma [CA] and [CA-S] were determined 2 h instead of 24 h after exercise. Platelet [CA] and [CA-S] remained unchanged throughout the study. Plasma [CA] increased after exercise in all groups (P<0.05) and returned to pre-exercise values within 0.5 h of recovery. Plasma sulphoconjugated noradrenaline concentration ([NA-S]) was elevated after exercise in the triathletes, long-distance runners and in controls [9.96 (SEM 0.84) nmol·1^–1, 11.8 (SEM 1.19) nmol·1^–1, 9.53 (SEM 1.10) nmol·l^–1, respectively;P<0.05] compared with resting values [7.13 (SEM 1.04) nmol·l^–1, 6.19 (SEM 0.56) nmol·l^–1, 6.76 (SEM 0.67) nmol·1^–1, respectively] and remained elevated after 0.5 h of recovery [9.94 (SEM1.14) nmol·l^–1, 10.96 (SEM 0.80) nmol·l^–1, 8.95 (SEM 0.99) nmol·l^–1, respectively;P<0.05]. In the long-distance runners and controls plasma [NA-S] remained elevated during 2 h of recovery [9.96 (SEM 0.76) nmol·l^–1, 9.03 (SEM 0.88) nmol·l^–1, respectively]. These results would indicate that plasma [NA-S] increases after sympathetic nervous system activation by an exhausting incremental exercise test and remain elevated up to 2 h after exercise.     

Kinetics of heart rate and catecholamines during exercise in humans

Summary To elucidate the role of factors other than the nervous system in heart rate (f _c) control during exercise, the kinetics off _c and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. Thef _c did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during whichf _c increased linearly. At the cessation of the exercise,f _c remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg · ml^–1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg · ml^–1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of thef _c increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats · min^–1 per 100 pg · ml^–1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase inf _c depends on plasma [NA].     

Mobilization of circulating leucocyte and lymphocyte subpopulations during and after short,anaerobic exercise

Summary A group of 11 healthy athletes [age, 27.4 (SD 6.7) years; body mass, 75.3 (SD 9.2) kg; height, 182 (SD 8) cm; maximal oxygen uptake, 58.0 (SD 9.9) ml · kg^–1 · min^–1] conducted maximal exercise of 60-s duration on a cycle ergometer [mean exercise intensity, 520 (SD 72) W; maximal lactate concentration, 12.26 (SD 1.35) mmol · l^–1]. Adrenaline and noradrenaline, and leucocyte subpopulations were measured flow cytometrically at rest, after 5-min warming up at 50% of each individual's anaerobic threshold (followed by 5-min rest), immediately after (0 min), 15 min, 30 min, and 1, 2, 4 and 24 h after exercise. Granulocytes showed two increases, the first at 15 min and, after return to pre-exercise values, the second more than 2 h after exercise. Eosinophils also increased at 15 min but decreased below pre-exercise values 2 h after exercise. Total lymphocytes and monocytes had their maximal increases at 0 min. Out of all lymphocyte subpopulations CD3^–CD16/CD56⁺- and CD8S⁺ CD45RO^–-cells increased most and had their maximal cell counts at 0 min. The CD3⁺-, CD4⁺CD45RO⁺-, CD8⁺ CD45RO⁺-, and CD19⁺- increased at 0 min, but had their maximum at 15 min. During the hours after exercise CD3^– CD16/CD56⁺-, CD3⁺CD16/CD56⁺-, CD8⁺CD45RO⁺- and CD8⁺ CD45RO^–-cells were responsible for the lymphocytopenia. The CD3⁺- and CD3^– CD16/CD56⁺-cells were lower 24h after exercise than before exercise. Adrenaline and noradrenaline increased during exercise. In conclusion, short anaerobic exercise led to a sequential mobilization of leucocyte subpopulations. The rapid increase of natural killer cells and monocytes may have been due to increased blood flow and catecholamine concentrations. We interpreted from these results that those cells forming the first line of defence can be mobilized faster and disappear out of circulation more rapidly than all other cell populations.     

Plasma testosterone and catecholamine responses to physical exercise of different intensities in men

Summary Plasma testosterone, noradrenaline, and adrenaline concentrations during three bicycle ergometer tests of the same total work output (2160 J·kg^–1) but different intensity and duration were measured in healthy male subjects. Tests A and B consisted of three consecutive exercise bouts, lasting 6 min each, of either increasing (1.5, 2.0, 2.5 W·kg^–1) or constant (2.0, 2.0, 2.0 W·kg^–1) work loads, respectively. In test C the subjects performed two exercise bouts each lasting 4.5 min, with work loads of 4.0 W·kg^–1. All the exercise bouts were separated by 1-min periods of rest.Exercise B of constant low intensity resulted only in a small increase in plasma noradrenaline concentration. Exercise A of graded intensity caused an increase in both catecholamine levels, whereas, during the most intensive exercise C, significant elevations in plasma noradrenaline, adrenaline and testosterone concentrations occurred. A significant positive correlation was obtained between the mean value of plasma testosterone and that of adrenaline as well as noradrenaline during exercise.It is concluded that both plasma testosterone and catecholamine responses to physical effort depend more on work intensity than on work duration or total work output.This work was performed within the Scientific Exchange Programme between the Institute of Experimental Endocrinology, Slovak Academy of Sciences in Bratislava and Medical Research Centre, Polish Academy of Sciences, Warsaw/Project 10.4/