Plasma catecholamines and heart rate at the beginning of muscular exercise in man

Summary The relationship between the time course of heart rate and venous blood norepinephrine (NE) and epinephrine (E) concentrations was studied in 7 sedentary young men before and during 3 bicycle exercises of 5 min each (respectively 23±2.8%, 45±2.6% and 65±2.4% , mean ±SE). During the low level exercise the change in heart rate is monoexponential ( =5.7±1.2s) and no increment above the resting level of NE (NE) or of E (E) occurs. At the medium and highest intensity of exercise: a) the change in heart rate is biexponential, for the fast and the slow component averaging about 3 and 80 s respectively; b) NE (but not E) increases continuously with time of exercise; c) at the 5th min of exercise heart rate increments are related to NE; d) between 20s and 5 min, at corresponding sampling times, the heart rate of the slow component is linearly related to NE. At exercise levels higher than 33% the increase in heart rate described by the slow component of the biexponential kinetic could be due to an augmented sympathetic activity revealed by increased NE blood levels.     

Heart rate variability during dynamic exercise in elderly males and females

It has been proposed that cardiac control is altered in the elderly. Power spectral analysis of heart rate variability (HRV) was performed on 12 male and 11 female elderly subjects (mean age 74 years) while at rest in supine and sitting positions, and at steady states during 5 min of exercise (35–95% peak oxygen consumption, V˙O_2peak). There were no differences in power, measured as a percentage of the total of the high frequency peak (HF, centred at about 0.25 Hz; 13% in males vs 12% in females), low frequency peak (LF, centred at 0.09 Hz; 25% in males and 22% in females), and very low frequency component (VLF, at 0.03 Hz; 66% in males and 69% in females) between body positions at rest. There was no difference in spectral power between male and female subjects. Total power decreased as a function of oxygen consumption during exercise, LF% did not change up to about 14 ml · kg⁻¹ · min⁻¹ (40% and 80% V˙O_2peak in males and females, respectively), then decreased towards minimal values in both genders. HF% power and central frequency increased linearly with metabolic demand, reaching higher values in male subjects than in female subjects at V˙O_2peak, while VLF% remained unchanged. Thus, the power spectra components of HRV did not reflect the changes in autonomic activity that occur at increasing exercise intensities, confirming previous findings in young subjects, and indicated similar responses in both genders. Accepted: 30 November 1999     

Changes in human heart rate during sleep following daily physical exercise

Summary Four fit, healthy young men (aged 20) volunteered for the experiment. After a 5 day control period, they marched for 6 consecutive days (from 09:00 h to 17:00 h) for 34 km/day at a speed of 6 km/h, with an energy expenditure of 35% of individual max. A recovery period of 5 consecutive days began immediately after the exercise period. Sleep records and electrocardiograms were taken every night during the three periods from 22:00 h to 06:00 h.During the exercise period the night time heart rates increased by about 10%, compared to the previous control condition, and returned to normal during the recovery period.The relation between heart rate changes and sleep stages remained identical throughout the three experimental periods. Three subjects showed an increase in heart rate during paradoxical sleep, compared to the preceding slow wave sleep, while one subject experienced the reverse.The tonic increases in heart rate are discussed in relation to changes in body temperature, sleep patterns, blood composition and hormonal status induced by the physical exercise performed.Supported by grant N 77/1198 from the Direction des Recherches et Etudes Techniques (Délégation Ministérielle pour l'Armement)     

Autonomic nervous control of the heart rate during isometric exercise in normal man

The relative contribution of the efferent components of the autonomic nervous system to the regulation of tachycardia induced by isometric exercise was assessed in 23 normal males. The isometric exercise (handgrip) was performed at the maximum intensity tolerated by the individual over a period of 10 s (maximal voluntary contraction — MVC) and at levels equivalent to 75, 50 and 25% of MVC for 20, 40 and 10 s, respectively. The study was performed both under control conditions and after pharmacological blockade with atropine (12 individuals) or propranolol (11 individuals). Under control conditions, the heart rate (HR) responses to isometric effort were dependent on the intensity and duration of the exercise, showing a tendency towards progressive elevation with the maintenance of muscular contraction at the levels studied. The tachycardia evoked by this effort was of considerable magnitude and of rapid onset, especially at the more intense levels of activity. Parasympathetic blockade markedly decreased tachycardia, which manifested itself during the first 10 s of exercise at all levels of intensity, whereas sympathetic blockade markedly modified the HR response after 10 s of effort at the 75 and 50% MVC levels. A slight depression of the tachycardiac response could be observed already after 10 s of maximum effort after propranolol. The present results suggest that the autonomic regulation of these responses is based on a biphasic mechanism, with the initial phase depending on the rapid withdrawal of the parasympathetic influence, followed by a marked sympathetic contribution to the induction of tachycardia after 10 s of isometric contraction or even a little before at maximum exertion.     

The effect of eccentric strength training on heart rate and on its variability during isometric exercise in healthy older men

The purpose of this study was to investigate if chronic eccentric strength training (ST) affects heart rate (HR) and heart rate variability (HRV) during sub-maximal isometric voluntary contractions (SIVC). The training group (TG) (9 men, 62 ± 2) was submitted to ST (12 weeks, 2 days/week, 2–4 sets of 8–12 repetitions at 75–80% peak torque (PT). The control group (CG) (8 men, 64 ± 4) did not perform ST. The HR and the HRV (RMSSD index) were evaluated during SIVC of the knee extension (15, 30 and 40% of PT). ST increased the eccentric torque only in TG, but did not change the isometric PT and the duration of SIVC. During SIVC, the HR response pattern and the RMSSD index were similar for both groups in pre- and post-training evaluations. Although ST increased the eccentric torque in the TG, it did not generate changes in HR or HRV.     

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.     

The influence of exercise intensity on the power spectrum of heart rate variability

Summary The power spectral analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in seven sedentary males at rest, during steady-state cycle exercise at 21 percent maximal oxygen uptake. (% V _{O 2max}), SEM 2%, 49% V_{O 2max}, SEM 2% and 70% V_{O 2max}, SEM 2% and during recovery. The RRV, i.e. the absolute power of the spectrum, decreased 10, 100 and 500 times in the three exercise intensities, returning to resting value during recovery. In the RRV power spectrum three components have been identified: (1) high frequency peak (HF), central frequency about 0.24 Hz at rest and recovery, and 0.28 Hz, SEM 0.02, 0.37 Hz, SEM 0.03 and 0.48 Hz, SEM 0.06 during the three exercise intensities, respectively; (2) low frequency peak (LF), central frequency about 0.1 Hz independent of the metabolic state; (3) very low frequency component (VLF), <0.05 Hz, no peak observed. The HF peak power, as a percentage of the total power (HF%), averaged 16%, SEM 5% at rest and did not change during exercise, whereas during recovery it decreased to 5%–10%. The LF% and VLF% were about 50% and 35% at rest and during low exercise intensity, respectively. At higher intensities, LF% decreased to 16% and VLF% increased to 70%. During recovery a return to resting values occurred. The HF component may reflect the increased respiratory rate and the LF peak changes the resetting of the baroreceptor reflex with exercise. The hypothesis is made that VLF fluctuations in heart rate might be partially mediated by the sympathetic system.     

Heart rate dynamics during a treadmill cardiopulmonary exercise test in optimized beta-blocked heart failure patients

BACKGROUND: Calculating the maximum heart rate for age is one method to characterize the maximum effort of an individual. Although this method is commonly used, little is known about heart rate dynamics in optimized beta-blocked heart failure patients. AIM: The aim of this study was to evaluate heart rate dynamics (basal, peak and % heart rate increase) in optimized beta-blocked heart failure patients compared to sedentary, normal individuals (controls) during a treadmill cardiopulmonary exercise test. METHODS: Twenty-five heart failure patients (49+/-11 years, 76% male), with an average LVEF of 30+/-7%, and fourteen controls were included in the study. Patients with atrial fibrillation, a pacemaker or noncardiovascular functional limitations or whose drug therapy was not optimized were excluded. Optimization was considered to be 50 mg/day or more of carvedilol, with a basal heart rate between 50 to 60 bpm that was maintained for 3 months. RESULTS: Basal heart rate was lower in heart failure patients (57+/-3 bpm) compared to controls (89+/-14 bpm; p<0.0001). Similarly, the peak heart rate (% maximum predicted for age) was lower in HF patients (65.4+/-11.1%) compared to controls (98.6+/-2.2; p<0.0001). Maximum respiratory exchange ratio did not differ between the groups (1.2+/-0.5 for controls and 1.15+/-1 for heart failure patients; p=0.42). All controls reached the maximum heart rate for their age, while no patients in the heart failure group reached the maximum. Moreover, the % increase of heart rate from rest to peak exercise between heart failure (48+/-9%) and control (53+/-8%) was not different (p=0.157). CONCLUSION: No patient in the heart failure group reached the maximum heart rate for their age during a treadmill cardiopulmonary exercise test, despite the fact that the percentage increase of heart rate was similar to sedentary normal subjects. A heart rate increase in optimized beta-blocked heart failure patients during cardiopulmonary exercise test over 65% of the maximum age-adjusted value should be considered an effort near the maximum. This information may be useful in rehabilitation programs and ischemic tests, although further studies are required.     

Effect of low-dose endurance training on heart rate variability at rest and during an incremental maximal exercise test

We evaluated the effects of low-dose endurance training on autonomic HR control. We assessed the heart rate variability (HRV) of 11 untrained male subjects (36.8 +/- 7.2 years) at rest and during an incremental maximal aerobic exercise test prior to a 7-week preparatory period and prior to and following a 14-week endurance training period, including a low to high intensity exercise session twice a week. Total (0.04-1.2 Hz), low (0.04-0.15 Hz) and high (0.15-1.2 Hz) frequency power of HRV were computed by short-time Fourier transform. The preparatory period induced no change in aerobic power or HRV. The endurance training period increased peak aerobic power by 12% (P < 0.001), decreased the HR (P < 0.01) and increased all HRV indices (P < 0.05-0.01) at absolute submaximal exercise intensities, but not at rest. In conclusion, low-dose endurance training enhanced vagal control during exercise, but did not alter resting vagal HR control.     

Short- and long-term effects of a single bout of exercise on heart rate variability: comparison between constant and interval training exercises

Heart rate variability (HRV) was assessed during the short- (within 1 h) and long- (within 48 h) term recovery following a single bout of either constant (CST) or interval training (SWEET) exercise performed at the same total physical work [9.4 (0.3) kJ kg^–1]. R-R intervals, systolic (SAP) and diastolic (DAP) arterial pressures were recorded in supine and upright positions before and 1, 24 and 48 h after the termination of the exercises in ten male subjects [mean (SEM), age 24.6 (0.6) years, height 177.2 (1.1) cm and body mass 68.5 (0.9) kg]. The parameters were also recorded in the supine position during the first 20 min following the end of the exercise. Spectral analysis parameters of HRV [total (TP), low- (LF), and high- (HF) frequency power, and LF/TP, HF/TP and LF/HF ratios] were determined over 5 min during each phase. Except for higher HF values in both supine and upright positions during the first hour following CST compared with SWEET, cardiovascular and HRV analysis responses were of the same magnitude after their termination. R-R intervals, TP, and HF/TP were significantly decreased while LF/TP and LF/HF were significantly increased during the early recovery, when compared with control values. This could be a response to the significant decrease in SAP and DAP at this time. Twenty-four and 48 h after the end of the exercise, HRV parameters were at the same levels as before exercises in the supine posture, but a persistent tachycardia continued to be observed in the upright posture, together with reduced TP values, showing that cardiovascular functions were still disturbed. The short-term HRV recovery seemed dependent on the type of exercise, contrary to the long-term recovery.     

Maximum oxygen consumption in dogs during muscular exercise and cold exposure

Maximum oxygen consumption for a short exhaustive work (Ex max) and for a severe cold stress (Ex max) were investigated in 8 dogs. Heart rate, plasma catecholamines and substrate concentrations were measured under both conditions. Mean C was lower than mean Ex max. Heart rate and plasma lactate were also lower during cold exposure than during exercise. Average plasma epinephrine concentrations were not significantly different and average plasma norepinephrine concentrations were similar under C and Ex max conditions. A positive correlation was found between plasma lactate and epinephrine concentrations measured under both conditions.It may be assumed that maximum oxygen consumption during muscular exercise is higher than during shivering thermogenesis. This difference does not seem to be due to differences in the involvement of the sympathico-adreno-medullary system.     

Sex-related differences in free plasma catecholamines in individuals of similar performance ability during graded ergometric exercise

Summary Sex-related differences of catecholamine responses were evaluated in nine healthy women and six age-matched men at rest and during incremental treadmill erxercise. Heart rate, oxygen uptake ( ), glucose and lactate blood levels as well as the free plasma catecholamines, noradrenaline and adrenaline, were determined. No significant differences were observed for these parameters between the two groups at rest. The females had relative and maximal running velocities similar to the males, which points to a comparable dynamic performance ability. However, at identical work loads, noradrenaline, adrenaline and glucose levels were significantly higher in women than in men. Lactate, heart rate and relative showed a similar tendency at submaximal exercise levels, indicating higher strain at identical stress levels in women. The reason for the higher sympathetic activity in women at identical work loads may be their relatively smaller skeletal muscle mass in relation to the loads during this test.Supported by Bundesinstitut für Sportwissenschaften, Cologne-Lövenich, FRG     

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 mental and physical demands on heart rate variability during computer work

The aim of the study was to evaluate the effect of physical and mental demands on heart rate variability- (HRV-) derived indices of autonomic activity. Ten healthy, female subjects performed two computer tasks: one with combined mental and physical demands and a reference task primarily consisting of physical demands. The combined task, which was performed once with a keyboard and once with a computer mouse, was a computerized version of the colour word conflict task (CWT). The CWT is highly mentally demanding due to the inherent perceptual conflict between a word stimulus and a colour stimulus. In the reference task (REF) the physical demands were comparable to CWT, while the mental demands were low. Finally, the subjects rested at the workplace (REST). Data on performance, heart rate (HR), mean arterial blood pressure (MAP), HRV, and urinary concentrations of catecholamines were obtained. The following frequency bands were applied for HRV: very low frequency (VLF, 0.00–0.04 Hz), low frequency (LF, 0.05–0.15 Hz), high frequency (HF, 0.16–0.40 Hz) and total power (TP, 0.00–0.40 Hz). Indices of sympathetic nervous activity (I_SNS) and parasympathetic nervous activity (I_PNS) were estimated as normalized powers in LF and HF bands: I_SNS=LF/(TP–VLF) and I_PNS=HF/(TP–VLF). Values are expressed as normalised units (nu). There was an increase in I_SNS during CWT [mouse: 0.490 (0.052) nu [ave (SEM)] and keyboard: 0.476 (0.039) nu] and REF [mouse: 0.453 (0.059) nu and keyboard: 0.489 (0.047) nu] compared to REST [0.397 (0.047) nu], but no difference between CWT and REF. Corresponding decreases were observed for I_PNS. HR and MAP were higher during CWT compared to REST. No effects were observed for excreted amounts of catecholamines. There were no differences between the computer mouse and the keyboard condition for I_SNS and I_PNS. In conclusion, an increase in I_SNS and a decrease in I_PNS were found in response to a physically demanding reference computer task. Addition of mental demands did not elicit any further effect on I_SNS and I_PNS, suggesting a significant influence of the physical rather than the mental demands during computer work. Electronic Publication     

Body position affects the power spectrum of heart rate variability during dynamic exercise

Summary The power spectrum analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in six men in supine (S) and sitting (C) postures at rest and during steady-state cycle exercise at about 14010, 28%, 45%, 67% of the maximal oxygen consumption (% VO_2max). The total power of RRV decreased exponentially as a function of exercise intensity in a similar way in both postures. Three components were recognized in the power spectra: firstly, a high frequency peak (HF), an expression of respiratory arrhythmia, the central frequency (f _central) of which increased in both S and C from a resting value of about 0.26 Hz to 0.42 Hz at 67% VO_2max; secondly, a low frequency peak (LF) related to arterial pressure control, the f _central of which remained constant at 0.1 Hz in C, whereas in S above 28% VO_2max decreased to 0.07 Hz; and thirdly, a very low frequency component (VLF; less than 0.05 Hz, no f _central). The power of the three components (as a percentage of the total power) depended on the body posture and the metabolic demand. HF% at rest was 30.3 (SEM 6.6) % in S and 5.0 (SEM 0.8) % in C. During exercise HF% decreased by about 30% in S and increased to 19.7 (SEM 5.5) % at 28% VO_2max in C. LF% was lower in S than in C at rest [31.6 (SEM 5.7) % vs 44.9 (SEM 6.4) %; P<0.05], remaining constant up to 28% VO_2max. At the highest intenstities it increased to 54.0 (SEM 15.6) % in S whereas in C it decreased to 8.5 (SEM 1.6) %. VLF represented the remaining power and the change was in the opposite direction to LF. The changes in power spectrum distribution of RRV during exercise depended on the intensity and the body posture. In particular, the LF peak showed opposite trends in S and C tasks, thus suggesting a different readjustment of arterial pressure control mechanisms in relation to the blood distribution and peripheral resistances.     

Circannual rhythm of exercise metabolic rate in humans

Summary Exercise metabolic rate was established by indirect calorimetry in 18 healthy subjects. Each subject was tested every month for 1 year. Four variables demonstrated a circannual rhythm and its acrophases occured in the following months:RQ in October; exercise metabolic rate in April; acceleration of heart rate during exercise in February; percentage of body fat in August.Supported by a grant from the National Institute of Food and Nutrition     

Cardiovascular responses of cardiac transplant patients to arm and leg exercise

This investigation compares the cardiovascular responses of normal (n=10) and cardiac transplant (n=14) subjects to peak arm and leg exercise. It also tests the hypothesis that the higher heart rate (f _c) in normal subjects during light (30 W) submaximal arm versus leg exercise is due to cardiac innervation. In cardiac transplant patients, power output, oxygen consumption ,f _c and rate pressure product were 54%, 28%, 7%, and 8% lower during peak arm than leg exercise, respectively. In normal subjects, power output, ,f _c and rate pressure product were 61%, 33%, 8%, and 11% lower during peak arm than leg exercise, respectively. In cardiac transplant patients there was no significant difference in absolutef _c during submaximal arm and leg exercise. In normal subjects, absolutef _c during arm and leg exercise was [mean (SD)] 97 (4) beats · min^–1 and 92 (4) beats · min^–1, respectively (P=0.07). Plasma noradrenaline was increased more during arm than leg exercise in both cardiac transplant and normal subjects. Maximal leg testing is useful when determining the capacity of cardiac transplant patients to perform arm work. The higher absolutef _c reported by other investigators for normal subjects during submaximal arm versus leg exercise may be mediated by cardiac innervation.     

Effect of exercise mode on heart rate variability during steady state exercise

This study examined the effect of exercise mode on geometrical, and time and frequency domain measures of heart rate variability (HRV) during steady-state, moderate intensity exercise of the same HR. Seventeen healthy, active male participants volunteered for this study and completed a treadmill determination. One week later, cardiorespiratory, perceptual and HRV measures were recorded during seated rest (15 min) and consecutive bouts (15 min) of steady-state exercise at 50 and 65% of maximal HR. Exercise was performed using either upper body (arm ergometer), lower body (cycle) or whole body (treadmill) modes. Separated by 1 week and in a random order, participants undertook the same procedures with the remaining exercise modes. Cardiorespiratory, perceptual and HRV responses were determined during rest and steady-state exercise and analysed by two-way (mode vs. stage) repeated measures ANOVA and post hoc pairwise comparisons. Apart from a reduced respiratory rate during lower body exercise, whole and lower body exercise resulted in similar cardiorespiratory, perceptual and HRV responses. Compared to whole or lower body exercise, upper body exercise resulted in significantly (P < 0.05) greater measures of HRV particularly those within the very low (0–0.04 Hz) and low (0.04–0.15 Hz) frequency bands, greater rating of perceived exertion and less oxygen consumption. Upper body, moderate intensity exercise resulted in greater HRV compared to whole or lower body exercise with further studies necessary to elucidate the mechanisms and clinical implications for this greater HRV. Part of this work has previously been presented at the 2004 Sports Medicine Australia National Conference, 6–9th October, Alice Springs, Australia.     

The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.     

Impact of the exercise mode on heart rate recovery after maximal exercise

Heart rate recovery 1 min after exercise termination (HRR-1) is a prognostic predictor. However, the influence of the exercise mode on HRR-1 is incompletely characterised. Twenty-nine young and healthy subjects and 16 elderly patients with chronic heart failure underwent cardiopulmonary exercise testing using cycle ergometer and treadmill ramp protocols in random order. HRR-1 and heart rate recovery 2 and 3 min after exercise (HRR-2, HRR-3) during active recovery and peak oxygen consumption (peak VO₂) were measured. In both healthy subjects (32 ± 14 vs. 27 ± 10 bpm) and HF patients (19 ± 8 vs. 14 ± 9 bpm), HRR-1 was faster after cycle exercise (p = 0.029; p for between group difference 0.94). In contrast, HRR-2 and HRR-3 were similar after both tests in both groups. Peak VO₂ was lower during cycle as compared to treadmill exercise in both groups. In conclusion, in both healthy subjects and HF patients, HRR-1 depends on the mode of exercise as peak VO₂ does.