Lipid metabolism during exercise

Summary Seven physically fit (well-trained, maximal oxygen uptake 69.6±4.4 ml×kg^–1×min^–1) and eight less fit (moderately trained, maximal oxygen uptake 56.1±5.7 ml×kg^–1×min^–1) healthy male subjects were exercised for 4 h by bicycle ergometry against a pedalling resistance calculated to cause oxygen consumption corresponding to approximately 30% of each individual's maximal oxygen uptake value. Respiratory exchange ratio was estimated at 1 h and blood glucose and lactate concentrations and muscle glycogen content at 2 h intervals. Muscle glycogen content decreased markedly during the first 2 h of exercise in the well-trained group but was similar after 4 h exercise in both groups. No major differences were observed between the two subject groups in blood variable concentrations. Calculations based on respiratory exchange ratio showed that the proportion of carbohydrates utilized in the total energy consumption was 14% in the physically fit group and 25% in the less fit group, thus supporting previous observations that more energy is derived by fat oxidation in well-trained than in less-trained individuals during submaximal work at relatively similar oxygen consumption levels.This study was supported by grant no. 9791/79/73 from the Research Council for Physical Education and Sports (Ministry of Education, Finland)It is deeply regretted that our honoured friend and mentor, Professor Esko Karvinen, PhD, MD, died during the preparation of this paper     

Effects of dichloroacetate on exercise performance in healthy volunteers

Dichloroacetate (DCA), a stimulator of the pyruvate dehydrogenase complex, decreases lactate levels and peripheral resistance and increases cardiac output. This study was performed to examine the effects of DCA on exercise performance in humans. Eight healthy male volunteers (age 20–28 years) were tested by bicycle spiro-ergometry using a microprocessor-controlled gas analysis system after infusion of DCA (50 mg/kg body weight) or saline. Prior infusion of DCA significantly reduced the increase of lactate levels during exercise when compared with infusion of saline (1.40±0.21 vs 2.10±0.09 mmol·l^–1 at 50% of the expected maximal working capacity, P<0.05; 8.53±0.45 vs 9.92±0.59 mmol·l^–1 at maximal working capacity, P<0.05). Oxygen uptake increased significantly after DCA when compared with saline from 7.5±0.4 vs 7.4±0.5 to 27.2±1.5 vs 23.7±1.7 (P<0.05) at anaerobic threshold and to 35.6±1.7 vs 30.5±1.0 ml · kg^–1 min^–1 (P<0.05) at maximal exercise capacity. Following DCA infusion the workload at which the anaerobic threshold was reached was significantly higher (160±7 vs 120±5 W, P<0.05) and the maximal working capacity was significantly increased (230±9 vs 209±8 W, P<0.05). In summary, DCA reduced the increase of lactate levels during exercise and increased oxygen uptake at the anaerobic threshold and at maximal working capacity, which was significantly increased. These results warrant further studies on a potential therapeutic application of DCA in patients with reduced exercise capacity.     

Acute EPOC response in women to circuit training and treadmill exercise of matched oxygen consumption

The purpose of the study was to evaluate the effects of circuit training (CT) and treadmill exercise performed at matched rates of oxygen consumption and exercise duration on elevated post-exercise oxygen consumption (EPOC) in untrained women, while controlling for the menstrual cycle. Eight, untrained females (31.3±9.1 years; 2.04±0.26 l min^–1 estimated VO_2max; BMI=24.6±3.9 kg/m²) volunteered to participate in the study. Testing was performed during the early follicular phase for each subject to minimize hormonal variability between tests. Subjects performed two exercise sessions approximately 28 days apart. Resting, supine energy expenditure was measured for 30 min preceding exercise and for 1 h after completion of exercise. Respiratory gas exchange data were collected continuously during rest and exercise periods via indirect calorimetry. CT consisted of three sets of eight common resistance exercises. Pre-exercise and exercise oxygen consumption was not different between testing days (P>0.05). Thus, exercise conditions were appropriately matched. Analysis of EPOC data revealed that CT resulted in a significantly higher (p<0.05) oxygen uptake during the first 30 min of recovery (0.27±0.01 l min^–1 vs 0.23±0.01 l min^–1); though, at 60 min, treatment differences were not present. Mean VO₂ remained significantly higher (0.231±0.01 l min^–1) than pre-exercise measures (0.193±0.01 l min^–1) throughout the 60-min EPOC period (p<0.05). Heart rate, RPE, V_E and RER were all significantly greater during CT (p<0.05). When exercise VO₂ and exercise duration were matched, CT was associated with a greater metabolic disturbance and cost during the early phases of EPOC.     

Effect of lowered muscle temperature on the physiological response to exercise in men

Summary The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O₂ uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12°C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5)°C to 30.5 (SD 1.7)°C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats · min^–1 after 6 min of exercise, to 4 (SD 2) beats · min^–1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.21 · min^–1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia.     

Effect of prior exercise at different pedalling frequencies on maximal power in humans

Summary The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev · min^–1, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake , whether performed at a pedalling frequency of 60 or 120 rev · min^–1, reduced maximal STPO generated at 120 rev · min^–1 to a much greater extent than maximal STPO at 60 rev · min^–1. After 6-min submaximal exercise at 60 rev · min^–1 mean reductions in maximal STPO measured at 120 and 60 rev · min^–1 were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev · min^–1, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev · min^–1, Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev · min^–1. Nevertheless, maximal STPO generated at 120 rev · min^–1 was reduced after exercise at 120 rev-min^–1 [20 (SD 13) %,P<0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev · min^–1. The present findings would suggest that exercise performed at 92 (SD 5)% , whether at 60 or at 120 rev · min^–1, selectively fatigues the faster fatigue-sensitive fibres resulting in a greater reduction in maximal STPO generated at 120 compared to 60 rev · min^–1. The greater fatigue of maximal STPO generated at 120 rev · min^–1 due to exercise performed at a power output of 236 (SD 30)W at 120 rev · min^–1 compared to 60 rev · min^–1 would suggest a relatively greater contribution of fast fatigue-sensitive fibres when higher movement frequencies and hence different muscle shortening velocities are used at this submaximal exercise intensity.     

Activation and inhibition of muscle and cutaneous postganglionic neurones to hindlimb during hypothalamically induced vasoconstriction and atropine-sensitive vasodilation

Summary Subcutaneous adipose tissue blood flow (ATBF) was examined in 8 subjects during 6 h exercise on a bicycle ergometer. The initial work load was 118 W corresponding to about 50% of maximal work capacity. The oxygen uptake increased from 0.26 l ·min^–1 at rest to about 1.6l·min^–1 during work. In 7 subjects ATBF increased, in 1 it remained constant. After 3 h exercise ATBF at an average reached values 3–4 times the control value. This increase was maintained for the remaining work periods. The increase was significant at the 5% level. Plasma free fatty acids increased 7-, plasma glycerol 10-fold during work.     

Adaptation of human left ventricular volumes to the onset of supine exercise

Summary The purpose of this study was to measure the changes and rates of adaptation of left ventricular volumes at the onset of exercise. Eight asymptomatic subjects, in whom intramyocardial markers had been implanted 3–6 years previously during aortocoronary bypass surgery, exercised in the supine position at a constant workload of 73.6 W for 5 min. Six also exercised first at 16.4 W, and then against a workload which progressively increased by 8.2 W every 15s. Cardiac volumes were measured by computer assisted analysis of the motion of the implanted markers. In the constant workload test, cardiac output increased rapidly from 5.7±1 min^–1 to 10.3±1.9 1 min^–1 by 2 min and then increased more slowly to 10.8±2.0 1 min^–1 by 5 min. The cardiac output increase was mainly due to an increase in heart rate from 68±12 beats min^–1 to 120±16 beats min^–1 with minimal changes in stroke volume. The time constant for the early increase in cardiac output was 45 s and for heart rate, 35 s. With progressively increasing workloads, there was an almost linear increase of heart rate and cardiac output, but these increased at a slower rate than during the early phase of the constant load exercise test. In conclusion: (i) rapid changes in cardiac output during supine exercise were produced by changes in heart rate; (ii) changes in stroke volume provided minor adjustments to cardiac output; (iii) the end-diastolic volume was almost constant.     

Changes in structure and function of the human left ventricle after acclimatization to high altitude

Summary To analyse the role of changes in structure and function of the left ventricle in determining cardiac function at rest and during exercise, several two-dimensional and Doppler echocardiographic measurements were performed on 11 healthy subjects immediately before an Himalayan expedition (Nun, 7135 m), during acclimatization (3 weeks) and 14 days after the return. At rest decreases were found in cardiac index (CI) (3.23 l · min^–1 · m^–2, SD 0.4 vs 3.82 l · min^–1 · m^–2, SD 0.58,P < 0.01), left ventricular mass (55.3 g · m^–2, SD 9.4 vs 65.2 g · m^–2, SD 13.5,P < 0.005) and left ventricular end-diastolic volume (LVEDV) (53.9 ml · m^–2, SD 6.9 vs 64.8 ml · m^–2, SD 9.1,P < 0.001) after acclimatization; by contrast the coefficient of peak arterial pressure to left ventricular end-systolic volume (PAP/ESV) (7.8, SD 1.6 vs 6.0, SD 1.8,P < 0.005) and mean wall stress [286 kdyn · cm^–2, SD 31 vs 250 kdy · cm^–2, SD 21 (2.86 N · cm^–2, SD 0.31 vs 2.50 N · cm^–2, SD 0.21),P < 0.005] increased. After return to sea level, low values of CI and mass persisted despite a return to normal of LVEDV and preload. A reduction of PAP/ESV was also observed. At peak exercise, PAP/ESV (8.7, SD 2.4 vs 12.8, SD 2.0,P < 0.0025), CI (9.8 l · min^–1 m^–2, SD 2.5 vs 11.61 · min^–1 · m^–2, SD 1.6,P < 0.05) and the ejection fraction (69%, SD 6 vs 76%, SD 4,P < 0.05) were lower after return to sea level than before departure. The depressed left ventricular performance after prolonged exposure to hypoxia may be related to changes in structure and function including reduction in preload, loss of myocardial mass and depression of inotropic state.     

Physiological and biomechanical comparison of roller skating and speed skating on ice

Summary Eight well trained marathon skaters performed all-out exercise tests during speed skating on ice and roller skating. To compare these skating activities in relation to the concept of training specificity, relevant physiological (V _O2,V _E, RER and heart rate) and biomechanical variables (derived from film and video analysis) were measured. There were no significant differences between oxygen uptake (50.5±8.0 and 53.3±6.7 ml·min^–1·kg^–1), ventilation (102.4±11.2 and 116.0±11.1 l·min^–1) or heart rate (174±12.2 and 176±14.5 min^–1) between speed and roller skating. In roller skating a higher RER (1.16±0.1 cf. 1.05±0.1) was found. Power, work per stroke and stroke frequency were equal. Due to a higher coefficient of friction the maximal roller skating speed was lower. The effectiveness of push-off and parameters concerning the skating techniques showed no differences. In roller skating a 7.5% higher angle of the upper leg in the gliding phase occurred. It is speculated that the blood flow through the extensor muscles might be higher in roller skating. It is concluded that roller skating can be considered as a specific training method which may be used by trained speed skaters in the summer period.     

Maximal oxygen uptake in 153 elderly Dutch people (69–87 years) who participated in the 1993 Nijmegen 4-day march

There are no studies on oxygen uptake of groups of physically active subjects aged over 70. This study describes the maximal oxygen uptake ( ) of 153 elderly people who completed the Nijmegen annual 4-day march (at least 30 km · day^–1) in 1993. A total of 97 men with a mean age of 76.7 (SD 4.6) and 56 women with a mean age of 72.8 (SD 3.6) years participated in the study. The was determined using incremental cycle ergometry; 91 men and 49 women completed a maximal exercise test. Criteria for maximal performance were respiratory exchange ratio equal to or greater than 1.00, vertilatory equivalent for oxygen equal to or greater than 30.00 and maximal heart rate equal to or greater than (beats · min^–1) 210 minus age (years). Mean maximal power output was 148.2 (SD 27.2) W and 120.4 (SD 20.5) W, mean · body mass^–1 was 26.8 (SD 4.9) ml · kg^–1 · min^–1 and 24.6 (SD 4.7) ml · kg^–1 · min^–1, mean maximal heart rate was 152 (SD 18), and 157 (SD 14) beats · min^–1 in men and women respectively. The mean · body mass^–1 was about 20% higher than reported in other studies on subjects over 70 years of age. Mean maximal heart rate was about 10 beats · min^–1 higher than predicted from the equation 220 — age. The negative effect of chronic disease on · body mass^–1 was smaller than in a sedentary reference population. The mean decline in · body mass^–1 with age was 0.46 and 0.38 ml·kg^–1·min^–1 per year in the men and women respectively, which is the same rate as found in younger subjects. It was concluded that regular exercise might substantially increase aerobic power in the physically active elderly, even when they have chronic disease, and that it is unlikely that there is an accelerated loss of aerobic power in physically active elderly people aged over 70 year.     

Lung diffusion capacity,oxygen uptake,cardiac output and oxygen transport during exercise before and after an Himalayan expedition

Studies were made of pulmonary diffusion capacity and oxygen transport before and after an expedition to altitudes at and above 4900 m. Maximum power (P _max) and maximal oxygen uptake (VO _2max) were measured in 11 mountaineers in an incremental cycle ergometer test (25W · min^–1) before and after return from basecamp (30 days at 4900 m or higher). In a second test, cardiac output (Q _c) and lung diffusion capacity of carbon monoxide (D _L,CO) were measured by acetylene and CO rebreathing at rest and during exercise at low, medium and submaximal intensities. After acclimatization, VO_2max and P _max decreased by 5.1% [from 61.0 (SD 6.2) to 57.9 (SD 10.2) ml·kg^–1, n.s.] and 9.9% [from 5.13 (SD 0.66) to 4.62 (SD 0.42) W·kg^–1, n.s.], respectively. The maximal cardiac index and DL,co decreased significantly by 15.6% [14.1 (SD 1.41) 1·min^–1 · m^–2 to 11.9 (SD 1.44)1·min^–1 m^–2, P<0.05] and 14.3% [85.9 (SD 4.36)ml·mmHg^–1 min^–t to 73.6 (SD 15.2) ml · mmHg^–1 -min^–1, P<0.05], respectively. The expedition to high altitude led to a decrease in maximal Q _c, oxygen uptake and D_L,CO. A decrease in muscle mass and capillarity may have been responsible for the decrease in maximal Q_c which may have resulted in a decrease of D _L,CO and an increase in alveolar-arterial oxygen difference. The decrease in D _L,CO especially at lower exercise intensities after the expedition may have been due to a ventilation-perfusion mismatch and changes in blood capacitance. At higher exercise intensities diffusion limitation due to reduced pulmonary capillary contact time may also have occurred.     

Histamine and Nt-methylhistamine in the circulation during intravenous infusion of histamine in normal volunteers

Plasma levels of histamine and N^t-methylhistamine were measured simultaneously by high performance liquid chromatography during the intravenous infusion of histamine acid phosphate in six normal volunteers. Progressive, dose-related increases in plasma histamine were noted, reaching a maximum value of 3.1±0.14 ng ml^–1 corresponding to a maximum infusion rate of 180 ng kg^–1 min^–1 (means±SEM). Increases in plasma histamine were accompanied by a significant dose-related fall in mean diastolic blood pressure (baseline 74.0±4.4 mm Hg falling to 60.0±3.3 mm Hg at maximum infusion rate,p<0.001) and an increase in pulse rate (baseline 76.3±2.8 beats min^–1 rising to 89.24 beats min^–1 at maximum infusion rate,p<0.05). All subjects exhibited facial flushing, the threshold plasma histamine level for this effect being 1.3±0.15 ng ml^–1 corresponding to an infusion rate of 60 ng kg^–1 min^–1. Elevation of plasma N^t-methylhistamine was seen in only one subject, who exhibited a level of 0.5 ng ml^–1 at the highest infusion rate. These results suggest that measurements of plasma N^t-methylhistamine are unlikely to provide a useful index of histamine release into the circulation.     

Intravenous instrumentation alters the autonomic state in humans

Intravascular instrumentation may induce syncope or presyncope. It is not known whether asymptomatic subjects also have autonomic reactions, albeit concealed. We addressed this issue by studying 44 healthy young male subjects of various levels of fitness, ranging from inactivity to athletic [mean maximal oxygen uptake was 49.1 (SD 10.7) ml·kg^–1·min^–1, range 28.7–71.9 ml·kg^–1·min^–1]. The autonomic response to venous cannulation was quantified by measuring heart rate before cannulation (HR1), after cannulation (HR₂), and after complete pharmacological autonomic blockade (HR₀ = the intrinsic heart rate). The sympathovagal balance before and after cannulation was computed as HR₁/HR₀ and HR₂/HR₀, respectively. The group means of heart rate and sympathovagal balance decreased significantly (paired Student's t-test P <0.01) from 62.5 to 59.9 beats·min^–, and from 0.71 to 0.68, respectively. The maximal decrease in heart rate was 8.8 beats·min^–1, and in the sympathovagal balance was 0.11. Our study demonstrated that the asymptomatic subjects responded to intravenous instrumentation with a concealed autonomic reaction. Thus, from our findings it would seem that intravenous instrumentation interferes with measurements relating to autonomic nervous system activity.     

Effect of high intensity interval training on 2,3-diphosphoglycerate at rest and after maximal exercise

Summary The purpose of this study was to examine the effect of intense interval training on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) levels at rest and after maximal exercise. Eight normal men, mean ± SE=24.2±4.3 years, trained 4 days·week^–1 for a period of 8 weeks. Each training session consisted of eight maximal 30-s rides on a cycle ergometer, with 4 min active rest between rides. Prior to and after training the subjects performed a maximal 45-s ride on an isokinetic cycle ergometer at 90 rev·min^–1 and a graded leg exercise test (GLET) to exhaustion on a cycle ergometer. Blood samples were obtained from an antecubital vein before, during and after the GLET only. Training elicited significant increases in the amount of work done during the 45-s ride (P<0.05), and also in maximal oxygen uptake ( max: Pre=4.01±0.13; Post=4.29±0.07 l·min^–1;P<0.05) during exercise and total recovery (Pre=19.14±0.09; Post=21.45±0.10 l·30 min^–1;P<0.05) after the GLET. After training blood lactate was higher, base excess lower and pH lower during and following the GLET (P<0.05 for all variables). Training caused no significant differences in erythrocyte 2,3-DPG levels at rest (Pre=11.8±0.7; Post=12.1±0.7 mol·g^–1 hemoglobin (Hb);P>0.05), at exhaustion (Pre=12.0±0.8; Post=11.2±0.8 mol·g^–1 Hb;P>0.05) or during 30 min of recovery from the GLET. Additionally, acute exercise (pre-training GLET) did not effect any change in 2,3-DPG at exhaustion or during recovery from exercise compared to resting values. The higher max and total recovery values observed after training appear to be unrelated to 2,3-DPG levels. Under the present conditions, the role, if any, of 2,3-DPG in enhancing tissue oxygenation during increased metabolic demand remains obscure.Supported by grants from Miles Laboratories, Elkhart, Indiana, and the Ball State Graduate Student Research Fund     

The effect of training on cardiovascular responses to arm exercise in individuals with tetraplegia

The aim of this study was to investigate the physiological responses to maximal and submaximal arm-cranking exercise in 21 individuals with tetraplegia (TP) and to evaluate the effect of a 3 and 6-month training period (mean frequency of 1.5 h · week^–1, mean intensity at 35% of the training time above 60% of the heart rate reserve) on these physiological responses. The TP were divided into 8 trained subjects (T), 7 untrained subjects (U) who started their training at the beginning of the study, and 6 sedentary subjects (S). All the subjects were tested at the beginning of training and after 6 months, whereas T and U were also tested in between, at 3 months. During maximal exercise, peak power output and peak oxygen uptake per kilogram bodymass were significantly higher in T (49.9 W and 14.2 ml·min^–1 · kg^–1 respectively) compared to U (20.7 W and 8.8 ml · min^–1 · kg^–1 respectively) and S (15.9 W and 7.4 ml · min^–1 · kg^–1 respectively), whereas all other peak responses showed tendencies to be higher in T. This is most likely to have been the result of participation in sport and the effect of it on performance capacity in T, although differences in completeness of the lesion may have influenced the results. No significant differences were found for submaximal and maximal responses after 3 or 6 months of training in either T and U or in S. This may have been due on the one hand to the vulnerability of the subjects to diseases and injuries and on the other hand to the low frequency of training. On an individual basis, however, remark able improvement was observed during the training period, especially for individuals in the U group. These results would suggest that a 3 or 6-month training period has no measurable positive effect on the fitness level of TP.     

Sympathetic response to maximal bicycle exercise before and after leg strength training

Summary Plasma catecholamine concentrations at rest and in response to maximal exercise on the cycle ergometer (278±15 watts, 6 min duration) have been measured on seven young active male subjects (19±1 years old; 80±3 kg; 176±3 cm) prior to and after a eight week leg strength training program (5RM, squat and leg press exercise). Strength training resulted in a significant increase in performance on squat (103±3 to 140±5 kg) and leg press exercise (180±9 to 247±15 kg) associated with a small significant increase in lean body mass (64.5±2.2 to 66.3±2.1 kg) and no change in maximal oxygen consumption (47.5±1.3 to 46.9±1.2 ml · kg^–1 · min^–1). Plasma norepinephrine (NE) and epinephrine (E) concentrations (pg · mL^–1) were not significantly different before and after training at rest (NE: 172±19 vs 187±30; E: 33±10 vs 76±16) or in response to maximal exercise (NE: 3976±660 vs 4163±1081; E: 1072±322 vs 1321±508). Plasma lactate concentrations during recovery were similar before and after training (147±5 vs 147±15 mg · dL^–1). Under the assumption that the central command is reduced for a given absolute workload on the bicycle ergometer following leg strength training, these observations support the hypothesis that the sympathetic response to exercise is under the control of information from muscle chemoreceptors.Supported by grants from NSERC, Government of Canada and FRSQ, Government of Quebec     

Effect of exercise on systemic blood pressure and heart rate in horses

Summary Carotid loops were prepared in 3 horses several months prior to the experiments. Systemic blood pressure was recorded at rest and during exercise by insertion of a plastic cannula into the carotid artery. The pressure transducer was fixed at the neck of the animal. The blood pressure signal was transmitted by telemetry.When the horses were standing under the rider, the following results were obtained: heart rate 38±5 beats · min^–1, systolic pressure 115±15, disstolic pressure 83±10, mean pressure 97±12, and pulse pressure 32±9 mm Hg. During steady gallop at a mean speed of 548±90 m · min^–1, heart rate rose to 184±23 beats · min^–1, systolic pressure to 205±23, diastolic pressure to 116±12, mean pressure to 160±20 and pulse pressure to 89±19 mm Hg. These values remained stable throughout the exercise period of 5–6 min.When the horses were exercised at stepwise increasing speed from walk through trot to gallop, both the mean arterial blood pressure and the pulse pressure rose in proportion to the running speed.     

Effects of exercise training on plasma catecholamines and blood pressure in labile hypertensive subjects

Summary Plasma catecholamine concentrations (norepinephrine, NE; epinephrine, E) were measured along with heart rate (HR) and blood pressure (BP) at rest in supine (20 min) and standing (10 min) positions and in response to cycle ergometer exercise (5 min; 60% estimated maximal aerobic power) in 12 hypertensive patients before and after 20 weeks of aerobic training on cycle ergometer (six males, one female) or by jogging (five males). In a control group of labile hypertensive patients (five males, two females), estimated maximal aerobic power as well as HR and BP at rest in the supine and standing positions and in response to exercise were not modified from the first to the second evaluation (43±4 vs 43±5 ml·kg^–1·min^–1). In comparison estimated maximal aerobic power significantly increased in both training groups (cycle: 38±4 to 43±4; jogging: 38±3 to 46±4 ml·kg^–1·min^–1). However HR and BP were not modified following training, except for small reductions in systolic (18.9 to 18 kPa: 142 to 135 mmHg) and diastolic pressures (13.3 to 12 kPa: 100 to 90 mmHg) (p<0.05) at standing rest in the cycle group. Changes in plasma E and NE concentrations at rest and in response to exercise were small and not consistent: plasma NE was lower at standing rest following cycle training, (559±95 vs 462±108 pg·ml^–1) but a similar reduction was observed in the control group (428±45 vs 321±28 pg·ml^–1); plasma E was lower at rest following cycle training (29±7 vs 12±8 pg·ml^–1), but was higher in response to exercise (137±24 vs 419±113 pg·ml^–1). These results are in accordance with previous reports which do not clearly demonstrate that physical training in hypertensive patients lowers BP and the activity or reactivity of the sympathetic system.     

Plasma volume change during heavy-resistance weight lifting

Summary Blood samples were obtained from six young men before, and over a 60-min period following a bout of heavy-resistance weight lifting to determine changes in plasma volume. Weight lifting consisted of three sets of four exercises (arm curl, bench press, bent-arm row, and squat) performed using 70% of one-repetition maximum for as many repetitions as possible. Plasma volume change was determined from haematocrit and haemoglobin concentration. During weight lifting, mean oxygen uptake and heart rate were 1.96 L · min^–1 and 158 bt · min^–1, respectively. Plasma volume was decreased –14.3% (p<0.05) immediately following exercise and –7.0% (p<0.05) at 15 min into recovery, but had returned to the resting level within 30 min. It was concluded that heavy-resistance weight lifting elicits a significant decrease in plasma volume, which is similar in magnitude to that observed during running and cycling at 80–95% of maximal oxygen uptake.     

The effect of glycogen availability on power output and the metabolic response to repeated bouts of maximal,isokinetic exercise in man

The relationship of glycogen availability to performance and blood metabolite accumulation during repeated bouts of maximal exercise was examined in 11 healthy males. Subjects performed four bouts of 30 s maximal, isokinetic cycling exercise at 100 rev · min^–1, each bout being separated by 4 min of recovery. Four days later, all subjects cycled intermittently to exhaustion [mean (SEM) 106 (6) min] at 75% maximum oxygen uptake Subjects were then randomly assigned to an isoenergetic low-carbohydrate (CHO) diet [7.8 (0.6)% total energy intake,n = 6] or an isoenergetic high-CHO diet [81.5 (0.4)%,n = 5], for 3 days. On the following day, all subjects performed 30 min cycling at 75% and, after an interval of 2 h, repeated the four bouts of 30 s maximal exercise. No difference was seen when comparing total work production during each bout of exercise before and after a high-CHO diet. After a low-CHO diet, total work decreased from 449 (20) to 408 (31) J · kg^–1 body mass in bout 1 (P < 0.05), from 372 (15) to 340 (18) J · kg^–1 body mass in bout 2 (P < 0.05), and from 319 (12) to 306 (16) J · kg^t-1 body mass in bout 3 (P < 0.05), but was unchanged in bout 4. Blood lactate and plasma ammonia accumulation during maximal exercise was lower after a low-CHO diet (P < 0.001), but unchanged after a high-CHO diet. In conclusion, muscle glycogen depletion impaired performance during the initial three, but not a fourth bout of maximal, isokinetic cycling exercise. Irrespective of glycogen availability, prolonged submaximal exercise appeared to have no direct effect on subsequent maximal exercise performance.