Existing and Training Induced Differences in Aerobic Fitness: Their Relationship to Physiological Response Patterns During Different Types of Stress

Aerobic fitness has been associated with various desirable psychological and physiological characteristies. Recently, attenuation of physiological reactivity during stressful situations was added to this list, although comparison of the stress responses of sportsmen and sedentary subjects has yielded equivocal results. The present study examined cardiovascular patterns rather than single variables, and tried to clarify these matters. Tasks were used that were known to increase blood pressure through different combinations of changes in cardiac output and vascular resistance. Autonomic nervous system dynamics underlying these response patterns were studied using preejection period as an index of β-adrenergic activity, and respiratory sinus arrhythmia as an index of vagal activity. Pre-existing differences in aerobic fitness in a sample of sedentary subjects were related to their responses during the stressful tasks and the recovery periods afterwards. This approach prevented confounding of the relationship between fitness and stress-reactivity with the psychological effects of regular exercise. Furthermore, it excluded the bias in psychological makeup that is introduced when subjects spontaneously engaged in sports are compared to non-exercising persons. To rule out a third (hereditary?) factor underlying both stress-reactivity and fitness, physiological responses before and after a seven-week training program were compared to those of subjects in a waiting list control group. Substantial individual differences in aerobic fitness were found in spite of the fact that all subjects reported low levels of habitual activity. During two active coping tasks, diastolic blood pressure reactivity and vagal withdrawal were negatively related to these pre-existing differences in fitness. No such relation was seen during a cold pressor test or during recovery from the tasks. Neither β-adrenergic cardiac reactivity nor heart rate responses were related to fitness, but the absolute heart rate during the tasks was lower in the more fit subjects. Seven weeks of training were not effective in changing either reactivity or recovery of any of the variables. The discrepancy between cross-sectional and longitudinal results in the present study suggests that training of longer duration is necessary to induce the psychological or physiological changes underlying reduced reactivity. The latter may include changes in cardiac vagal/sympathetic balance or in adrenoceptor sensitivity. Alternatively, both psychological and physiological determinants of stress-reactivity may be related to aerobic fitness at a dispositional level.     

Acute Emotional and Psychophysiological Effects of Aerobic Exercise

An experiment was conducted to examine the acute emotional and psychophysiological effects of a single bout of aerobic exercise. Forty active and 40 inactive college students were randomly assigned to an aerobic exercise or a waiting-period control condition. Self-report measures of mood and cardiovascular response measures to challenging cognitive tasks were collected before and after the 20-min exercise/control period to examine any exercise-induced changes. The results indicated that mood was significantly altered by the exercise activity, with reductions in tension and anxiety specifically evident. Exercise was not found to have any effects on cardiovascular reactivity. A test of aerobic fitness confirmed fitness differences between active and inactive participants, but no mood or reactivity effects related to activity status were obtained. These results suggest that both active and inactive individuals experience acute reductions in anxiety following single bouts of exercise, even in the absence of changes in cardiovascular reactivity. Implications for the continued investigation of the acute effects of exercise are discussed.     

Psychophysiological responses to the Stroop Task after a maximal cycle ergometry in elite sportsmen and physically active subjects.

Physical fitness moderates the psychophysiological responses to stress. This study attempts to determine whether the degree of fitness could affect the response to physical and psychological stress after comparing two groups of men with good physical fitness. Saliva samples from 18 elite sportsmen, and 11 physically active subjects were collected to determine hormonal levels after carrying out a maximal cycle ergometry. Heart rate and skin conductance level were continuously recorded before, during, and after a modified version of the Stroop Color-Word Task. With similar scores in trait anxiety and mood, elite sportsmen had lower basal salivary testosterone, testosterone/cortisol ratio, and HR before an ergometric session than physically active subjects, but no differences were found in salivary cortisol and blood pressure. Salivary testosterone and cortisol responses were lower and testosterone/cortisol ratio responses higher in elite sportsmen. During the Stroop Task, elite subjects showed lower heart rate and skin conductance level over the entire measurement period, and greater heart rate recovery with respect to the baseline values than physically active subjects. The effects of two standardised laboratory stressors on a set of psychophysiological variables were different when elite sportsmen and physically active subjects were compared.     

Electrodermal Lability and Myocardial Reactivity to Stress

The relationship between electrodermal lability and myocardial reactivity to stress was examined in male undergraduates, who were classified as electrodermally labile (n = 19) or stabile (n = 19) based on the frequency of nonspecific skin conductance responses at rest. Heart rate, pre-ejection period, cardiac output, and skin conductance responses were recorded at rest, during task instructions, and during two mental arithmetic tasks that varied in level of difficulty. As predicted, labiles exhibited greater myocardial reactivity to the task instructions and the tasks than did stabiles, with more persistent group differences emerging for pre-ejection period and cardiac output than for heart rate. The group differences did not vary as a function of task difficulty, but did decline over time. These results support a positive relationship between electrodermal lability and beta-adrenergic myocardial reactivity to stress, particularly under conditions of task novelty or uncertainty, and suggest that electrodermal lability is related fundamentally to arousal and reactivity processes.     

Exercise training in healthy type A middle-aged men: effects on behavioral and cardiovascular responses

Thirty-six healthy Type A men (means = 44.4 years) were randomly assigned to either an aerobic exercise training group or a strength and flexibility training group. Subjects completed a comprehensive psychological assessment battery before and after the exercise programs consisting of behavioral, psychometric, and psychophysiological testing. The behavioral assessment consisted of repeated Type A interviews that were videotaped for subsequent component analyses. The psychometric testing included two self-report questionnaires to assess Type A behavior. The psychophysiological test consisted of a standard behavioral challenge, a mental arithmetic task, performed while cardiovascular responses were monitored. Aerobic exercise (AE) training consisted of 12 weeks of continuous walking or jogging at an intensity of at least 70% of subjects' initial maximal oxygen consumption (VO2max) as determined by an initial treadmill test. Strength and flexibility (SF) training consisted of 12 weeks of circuit Nautilus training with no aerobic exercise. After 12 weeks of exercise, the AE group increased their VO2max by 15%, while the SF group did not change. Both groups experienced decreases in overt behavioral manifestations of the Type A behavior pattern and self-reported Type A traits. However, the AE group showed an attenuation of heart rate, systolic and diastolic blood pressure, and estimated myocardial oxygen consumption (MVO2) during the task and had lower blood pressure, heart rate, and (MVO2) during recovery. In contrast, the SF group showed a significant reduction only in DBP during the task, which was likely due to habituation. These results support the use of aerobic exercise as a method for reducing cardiovascular risk among healthy Type A men.     

The effect of participation in an exercise training program on cardiovascular reactivity in sedentary middle-aged males.

Exaggerated cardiovascular reactivity to mental stressors may be a risk factor for cardiovascular disease. To determine if participation in a moderate intensity aerobic exercise training program reduces cardiovascular reactivity to laboratory stressors, 40 sedentary middle-aged males were randomly assigned: training group (n = 25) and control group (n = 15). Cardiovascular reactivity during and after three mental stressors (passive responding, push-button Stroop and verbal Stroop) and mild exercise (bicycle ergometer) was assessed before and after an 8-week intervention. VO2(peak) was determined using the Balke protocol. Among 19 subjects who completed the training, VO2(peak) increased 13.7%. Also, trained compared to untrained subjects showed significant reductions in baseline and absolute heart rate responses to all stressors. Baseline adjusted heart rates were significantly lower during push-button Stroop recovery and during verbal Stroop. Blood pressure, T-wave amplitude, finger pulse amplitude and pulse transit time responses were unaffected by exercise training. It was concluded that participation in a short-term, moderate intensity aerobic exercise training program may have a cardioprotective effect by significantly reducing absolute and baseline-adjusted heart rate responses to stressors.     

Influence of aerobic exercise training and relaxation training on physical and psychologic health following stressful life events

An experiment was conducted to determine whether aerobic exercise training or relaxation training would be effective for reducing the deleterious effects of life stress on physical and psychologic health. Over 1000 college students were surveyed, and 55 of those who reported experiencing a high number of negative life events over the preceding year were assigned to an aerobic exercise training condition, a relaxation training condition, or a no-treatment control condition. Physical and psychologic health were assessed with self-report measures before, halfway through, immediately following, and 8 weeks after the 11-week training (and control) period. Heart rate data collected during a treadmill test indicated that the aerobic exercise training was effective for improving cardiovascular fitness. Psychologic measures indicated that the exercise training condition was more effective than the other two conditions for reducing depression during the first 5 weeks of training. No differences were found among the conditions on self-report measures of physical health. These findings suggest that aerobic exercise training may be useful for reducing the severity and duration of depressive reactions following stressful life change.     

Failure to alter sympathoadrenal response to psychosocial stress following aerobic training

This experiment assessed the impact of aerobic training on sympathoadrenal, heart rate and subjective responses to psychosocial stress. Subjects were six previously sedentary males who demonstrated marked improvement in fitness level following 10 weeks of training. Plasma samples, heart rate and subjective arousal ratings were obtained prior to, during, and following exposure to stressful mental tasks within a laboratory session. With the exception of training-related bradycardia which was manifest throughout the session, no changes in plasma epinephrine and norepinephrine concentrations, heart rate or subjective reactivity or recovery were seen. These findings are inconsistent with the hypothesized beneficial effects of aerobic training on stress-response. Methodological factors such as self-selection inherent in previous correlation work or the duration of the training program should be considered in this context. The potential contribution of training-related bradycardia to enhanced coping with challenging situations is explored.     

The Relationship Between Cardiovascular Responses in the Laboratory and in the Field

The psychophysiological responses to laboratory stressors are often examined because it is believed that such responses relate to responsiveness in real life situations. This belief has seldom been tested. The changes in heart rate, pulse transit time, and respiration rate produced by a variety of laboratory tasks (active and passive coping and physical exercise) were related to ambulatory measures of heart rate in 32 young men. The field measures were the difference in heart rate between the waking day and when asleep, and estimates of the variability of heart rate during the day, derived from time series analyses. Average changes in heart rate and pulse transit time during specific tasks did not relate consistently to heart rate in the field. However, an active coping index, derived from the ratio of the peak heart rate during an active coping task to the peak during physical exercise related to all the field measures of heart rate responsiveness. This index, which may relate to measures of additional heart rate and heightened sympathetic response to stress, also correlated positively with Trait Anxiety and elevated basal sympathetic arousal, as measured by skin conductance level. Measures of the cardiovascular response to a passive coping task, the cold pressor, and exercise did not relate to heart rate responses in the field. The findings suggest that heightened cardiac responsiveness in real life is exhibited by subjects who show elevated peak responses to active coping stressors specifically.     

Psychophysiological response of ADHD children to reward and extinction

In this study, we examined heart rate and skin conductance levels of 18 children with attention-deficit hyperactivity disorder (ADHD) and 18 normal children as they performed a repetitive motor task during reward and extinction conditions. Fowles (1980, Psychophysiology, 17, 87–104; 1988, Psychophysiology, 25, 373–391) suggested that psychophysiological responsivity reflects activity in two of Gray's (1982, The neuropsychology of anxiety, Oxford University Press; 1987, The psychology of fear and stress, Cambridge University Press) motivational systems; heart rate reactivity during reward reflects activity in the behavioral activation system, and skin conductance reactivity during extinction reflects activity in the behavioral inhibition system. As predicted, control children showed increased heart rate when reward was present and increased skin conductance when reward was removed. Compared with controls, ADHD children failed to show increased skin conductance levels during extinction, suggesting a weak behavioral inhibition system. ADHD children also displayed faster heart rate habituation to reward.     

Influence of a brief aerobic training program on heart rate and subjective response to a psychologic stressor

An experiment was conducted to determine whether a brief program of aerobic exercise would reduce the heart rate and subjective responses of high- and low-fit subjects to a psychologic stressor. Thirty-four high-fit and 34 low-fit subjects were exposed to a moderate stressor (recall of digits backwards test) while their heart rates and subjective responses were monitored. Approximately half of the high- and low-fit subjects then participated in a 13-week aerobic exercise training program, whereas the other subjects did not. After the 13-week period, the subjects were again exposed to the stressor. Results indicated that a) in the pretest the low-fit subjects showed a greater heart rate response to the stressor than the high-fit subjects, b) the training program was effective for increasing subjects' levels of aerobic fitness, and c) the training program was effective for reducing the heart rate response to the stressor of low-fit subjects. These findings provide support for the relationship between fitness and the response to psychologic stressors and they suggest that aerobic training may be an effective way of helping low-fit persons deal with psychologic stressors.     

Microcomputer Servo-controlled Bicycle Ergometer System for Psychophysiological Research

Steady state exercise is widely used for psychophysiological studies in which a constant heart rate at a predetermined level is desired. We have developed a microcomputer servo-controlled bicycle ergometer system that can be used for administering steady state exercise. Fourteen healthy male subjects, with a wide range of fitness levels (measured by VO2max) were exercised to either a fixed workload (130 watts) or a predetermined heart rate level (servo-heart rate) of 122 bpm (i.e., 65% of maximum calculated heart rate for the sample). Servo-heart rate was implemented using a feedback loop that automatically adjusted workload to compensate for immediate variations in heart rate, resulting in a more consistent heart rate. Heart rate varied from the predetermined value by 17 bpm during fixed workload but only 3 bpm during servo-heart rate (p less than .05). Therefore, by using the microcomputer servo-controlled bicycle ergometer, heart rate was maintained at a predetermined level regardless of the subject's fitness level. VO2max and workload during servo-heart rate were significantly correlated (r = .85, p less than .05). Therefore, the workload necessary to maintain heart rate at a constant level may provide an approximate index of aerobic fitness level.     

The pupil response as an indicator of user experience in a digital exercise game

To study whether psychophysiological indicators are suitable measures of user experience in a digital exercise game (exergame), a laboratory study employing both psychophysiological and self‐report measures was conducted. Sixty‐six participants cycled for 10 min on an ergometer while pupil diameter, skin conductance, and heart rate were measured; afterward, they completed a user experience questionnaire. The participants performed under three experimental conditions varying between subjects: active gaming (participants controlled the altitude of a digital bird by varying their pedal rate in order to catch letters flying across the screen), observing a game (they observed a replay of another participant’s game), and no‐game (blank screen). Only the gaming condition showed evidence for statistically significant pupil dilations—indicating emotional arousal—in response to game events (catching a letter) or corresponding points in time. The observational condition did not differ statistically from the no‐game control condition. Self‐reports also indicated that the gaming condition was rated most fun and least demanding. Other psychophysiological indicators (heart rate, skin conductance) showed no systematic effects in response to game events, rather they steadily increased during training. Thus, pupil responses were shown to be suitable indicators of positive emotional reactions to game events and user experience in a (training) game.     

Relaxation and skin conductance feedback in the control of reactions to cognitive tasks

Peripheral physiological activity and verbal ratings of tension and nervousness were assessed during instructed relaxation, and relaxation assisted by feedback of skin conductance level (SCL). Sixteen volunteers attempted to use each strategy in turn in a cross-over design. Responses were monitored both during quiet relaxation, and throughout the performance of taxing cognitive tasks.The electrodermal feedback made no difference to the reductions in SCL, heart rate or subjective ratings, when relaxation was carried out in undisturbed conditions. Following training, reactions to cognitive tasks were attenuated. It is suggested that while SCL feedback may aid the management of reactivity, it has little impact in the short term on depth of relaxation achieved by instructional programmes.     

P300, N400, aerobic fitness, and maximal aerobic exercise

Electrophysiological effects of aerobic fitness and maximal aerobic exercise were investigated by comparing P300 and N400 before and after a maximal cycling test. Event-related potentials (ERPs) were obtained from 20 students divided into two matched groups defined by their aerobic fitness level (cyclists vs. sedentary subjects). The session of postexercise ERPs was performed immediately after body temperature and heart rate returned to preexercise values. At rest, no significant differences were observed in ERP parameters between cyclists and sedentary subjects. This finding argued against the hypothesis that ERP modifications may be directly assumed by aerobic fitness level. The postexercise session of ERPs showed a significant P300 amplitude increase and a significant P300 latency decrease in all subjects. Similarly, N400 effect increased significantly after the maximal exercise in all subjects. ERP changes were of the same magnitude in the two groups. The present study argues for a general arousing effect of maximal aerobic exercise, independently of the aerobic fitness level.     

Phasic Cardiac Reactivity to Psychological Stress as a Function of Aerobic Fitness Level

Cardiovascular adjustments to physical exertion are known to be affected by aerobic fitness level. This raises the possibility that the cardiovascular responses associated with psychological stress may also be related to aerobic fitness. This study was undertaken to determine if phasic cardiac reactivity to stress would be affected by aerobic fitness level, and to make inferences regarding the autonomic mechanisms which might mediate such an effect. Twenty-four males were given a standard physical fitness test and then divided into high and low aerobic fitness level groups. Within two weeks of this assessment, the heart rate and electrocardiographic T-wave amplitude responses of these subjects were monitored during the performance of hard and easy versions of a mental arithmetic task. Analysis of the heart rate data revealed no aerobic fitness level effect. There was, however, greater T-wave amplitude attenuation in the low as compared to the high aerobic fitness level group on hard trials. This pattern of results suggests that psychologically-elicited sympathetic cardiac reactivity is reduced by enhanced aerobic fitness level.     

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.     

Symptom-Specific Psychophysiological Responses in Chronic Pain Patients.

Symptom-specific psychophysiological responding was assessed in 20 chronic back pain patients, 20 patients suffering from temporomandibular pain and dysfunction, and 20 matched healthy controls. Surface EMG from the lower and upper back, the masseter, and the biceps muscles, and heart rate and skin conductance level were continuously recorded during adaptation, resting baseline, and stressful and neutral imagery phases. Univariate and multivariate analyses of variance were performed on raw data as well as data corrected for autocorrelation. The results showed significantly higher EMG reactivity which was lateralized to the left side at the patients' site of pain but not distal sites. This hyperreactivity was observed only during stressful imagery. The healthy controls displayed a significantly higher response in heart rate, but skin conductance level was not significantly different. The results are interpreted as indicative of idiosyncratic muscular response patterns to personally relevant situations at the site of pain in patients suffering from chronic muscular pain.     

Arterial blood pressure and general sympathetic activation in essential hypertension during stimulation

We asked whether exaggerated blood pressure (BP) reactivity in patients with essential hypertension (HT) is a sign of specific activation of the cardiovascular system or of generalized sympathetic activation. Fourteen patients with essential hypertension and 14 matched normotensive (NT) controls were subjected to tasks involving attentional demands, mental arithmetic, a cold pressor test and isometric muscular contraction. Systolic and diastolic BPs, skin and muscle blood flows, heart rate, skin conductance level and fluctuations during each task were recorded. Urine samples for determination of epinephrine and norepinephrine excretion were collected after task completion. All tasks caused BP increases in both groups. HT showed greater absolute and percentage BP reactivity than NT during isometric muscle contraction. Variables for which reactivity differences were observed were poorly correlated across tasks both in HT and NT, whereas resting values prior to each task were highly correlated in both groups. Skin conductance activity, epinephrine and norepinephrine excretion rates being examples of non-cardiovascular sympathetic nervous system (SNS) indicators did not separate HT from NT. Thus, the exaggerated pressor response in HT is not accompanied by signs of generalized SNS activation.     

Influence of age and moderate-intensity exercise training on heart rate variability in young and mature adults.

The purpose of this study was to examine the influence of age and moderate-intensity exercise training on heart rate variability (HRV), and to elucidate further the mechanism of training-induced bradycardia and cardioprotection. Electrocardiograms were recorded from 12 young (18-24 yrs) and 12 mature (29-43 yrs) individuals during supine rest and submaximal moderate exercise. Recordings were obtained prior to, midway, and following 16 weeks of aerobic exercise training designed to improve cardiorespiratory fitness and health. Training resulted in augmented estimated VO2max and bradycardia during rest and submaximal exercise. Total and low frequency components of HRV during exercise were significantly increased for the mature subjects following training whereas other measures of HRV were not significantly changed for either group. It was concluded that training of moderate intensity was insufficient to induce changes in the autonomic control of heart rate for young to mature subjects. The lack of significant HRV changes may suggest the existence of a vagal critical point, below which training-induced increases in vagal modulation may be forthcoming, and above which changes in vagal modulation may be negligible. Training-induced bradycardia and the cardioprotective effect of regular aerobic exercise may result from factors other than an increased vagal modulation.