Phasic cardiac reactivity to psychological stress as a function of aerobic fitness level

Cardiorespiratory fitness and laboratory stress: a meta-regression analysis

We performed a meta-regression analysis of 73 studies that examined whether cardiorespiratory fitness mitigates cardiovascular responses during and after acute laboratory stress in humans. The cumulative evidence indicates that fitness is related to slightly greater reactivity, but better recovery. However, effects varied according to several study features and were smallest in the better controlled studies. Fitness did not mitigate integrated stress responses such as heart rate and blood pressure, which were the focus of most of the studies we reviewed. Nonetheless, potentially important areas, particularly hemodynamic and vascular responses, have been understudied. Women, racial/ethnic groups, and cardiovascular patients were underrepresented. Randomized controlled trials, including naturalistic studies of real-life responses, are needed to clarify whether a change in fitness alters putative stress mechanisms linked with cardiovascular health.

Effects of physical exercise on anxiety, depression, and sensitivity to stress: a unifying theory

Until recently, claims for the psychological benefits of physical exercise have tended to precede supportive evidence. Acutely, emotional effects of exercise remain confusing, both positive and negative effects being reported. Results of cross-sectional and longitudinal studies are more consistent in indicating that aerobic exercise training has antidepressant and anxiolytic effects and protects against harmful consequences of stress. Details of each of these effects remain unclear. Antidepressant and anxiolytic effects have been demonstrated most clearly in subclinical disorder, and clinical applications remain to be exploited. Cross-sectional studies link exercise habits to protection from harmful effects of stress on physical and mental health, but causality is not clear. Nevertheless, the pattern of evidence suggests the theory that exercise training recruits a process which confers enduring resilience to stress. This view allows the effects of exercise to be understood in terms of existing psychobiological knowledge, and it can thereby provide the theoretical base that is needed to guide future research in this area. Clinically, exercise training continues to offer clinical psychologists a vehicle for nonspecific therapeutic social and psychological processes. It also offers a specific psychological treatment that may be particularly effective for patients for whom more conventional psychological interventions are less acceptable.

Relations among memory performance, mental workload and cardiovascular responses

The levels of processing paradigm has been a powerful research framework in the study of memory for close to a quarter century. However, an objective index of depth of processing is still lacking. Two experiments using lists of words, presented to male subjects, wee performed to compare the effects of depth of processing, rate of presentation, and task incentive on recognition memory performance, self-reported workload, and cardiovascular responding. Memory performance results from the two experiments demonstrated higher recognition levels associated with deeper processing and slower presentation rates. Deeply encoded items were associated with faster recognition latencies. Self-reported workload levels were higher for deeper processing and faster presentation rates. Cardiovascular responses were generally amplified with the addition of a task incentive. Increased blood pressure was associated with faster presentation rates. Increased heart rate and decreased T-wave amplitude (i.e., increased sympathetic activity) were uniquely associated with the deep encoding of information presented at the fastest rate. This particular encoding condition was associated with increased recognition levels. Deeply encoded items were associated with increased suppression of heart rate variability during recognition. This combination of behavioral and cardiovascular measures may provide the basis for an objective index of depth of processing.

Bradycardia during baroreflex stimulation and active or passive stressor tasks: cardiorespiratory fitness and hostility

We examined whether the resting bradycardia associated with cardiorespiratory fitness extends to lowered heart rate (HR) and mean arterial pressure during novel passive or active laboratory stressors and to a longer heart period during stimulation of the carotid-cardiac vagal baroreflex, independently of the Type A behavior pattern (TABP) and hostility. Forty-four normotensive Caucasian men (18-35 years of age) completed the Structured Interview for TABP, the Cook-Medley Hostility Scale, and a peak oxygen uptake (Vo2peak) test. Vo2peak was inversely related to HR prior to, during, and after each stressor and was positively related to heart period during baroreflex testing. Hostility was inversely related to heart period during baroreflex testing. TABP had no effects. Our findings indicate that cardiorespiratory fitness and low hostility are independently associated with a bradycardia during stimulation of the carotid-cardiac baroreflex, consistent with a possible enhancement of cardiac vagal tone.

Heart rate response to psychological stressors of individuals possessing resting bradycardia

The authors examined the relation between trained and inherent bradycardia and heart rate (HR) and T-wave amplitude response to psychological stressors. They compared cardiac responses to two psychological stressors of 10 trained male runners (MVo2max = 75 mL/kg-1 min-1) possessing low resting heart rate (M = 58 bpm), 10 untrained men (MVo2max = 58 mL/kg-1 min-1) with inherently low resting heart rate (M = 58 bpm), and 10 unconditioned men (MVo2max = 51 mL/kg-1 min-1) with normal resting heart rate (M = 69 bpm). All participants completed a maximal oxygen consumption treadmill test, an easy and a hard mental arithmetic task, and the Stroop Color and Word Test. Their analysis of the data revealed no significant differences in relative heart rate response or T-wave amplitude between groups during or after any stressor. In contrast, absolute heart rates during and after mental arithmetic and during the Stroop test were significantly lower for both the trained and inherently low groups compared with the control group. These findings suggest that the lower absolute HR response during and after stressors was influenced by both aerobic training and genetic inheritance.

Mental challenge elicits "additional" increases in heart rate during low and moderate intensity cycling

The combined effects of exercise and mental challenge on heart rate (HR) and T-wave amplitude (TWA) were studied. Twenty male students cycled at low (40% of their relative maximal HR reserve (MHRR), for 15 min) and medium (60% MHRR, for 10 min) intensity exercise workloads. Subjects performed a series of mental arithmetic problems for one minute each time: two min before cycling, 10 min into low intensity cycling, 10 min into medium intensity cycling, and two and 20 min, respectively, after cycling. During both exercise workloads, the mental arithmetic elicited significant additional increases in HR. Although TWA decreased in response to mental arithmetic at rest, no changes in TWA were observed in response to mental task during exercise. However, TWA increased significantly following the mental challenge. These results suggest that even a mild mental challenge is capable of inducing further changes in the autonomic response during low and moderate exercise.

The combined effects of orthostatic and mental stress on heart rate, T-wave amplitude, and pulse transit time

The purpose of the present study was to determine whether cardiovascular reactivity to mental stress may be comparable in sitting and standing postures. Fifteen healthy males performed two 1-min mental arithmetic tasks, either while sitting or while standing, in counterbalanced order. Heart rate, pulse transit time, and T-wave amplitude were recorded in the last 10 s of the minute before, during, and after the mental arithmetic. Reactivity scores for each of the dependent measures were computed by calculating the percentage change from baseline values. Data were analyzed with multivariate and univariate repeated measures analysis of variance. Heart rate reactivity to the combination of orthostatic and mental stress was greater than to either stressor alone. Cardiac-sympathetic reactivity was greater in response to orthostatic than to mental stress as revealed by greater changes in T-wave amplitude and pulse transit time in response to the former. No additional decreases in T-wave amplitude, in response to mental stress, were observed during standing, but pulse transit time decreased in the same situation. However, no changes in pulse transit time in response to mental stress were observed in the sitting position. These results demonstrate that cardiovascular reactivity to mental stress depends on the body position in which the stressor is encountered.

Cardiac response of trained and untrained males to a repeated psychological stressor

The authors examined cardiac response to repeated exposure to a psychological stressor of aerobically conditioned (n = 15) and unconditioned subjects (n = 15). Heart rate and electrocardiographic T-wave amplitude responses of 10 trials of the Stroop Test were monitored during and after performance. Both groups' adaptation patterns were similar, with a plateauing of heart rate response after the third trial. Compared with the unconditioned group, however, the aerobically conditioned subjects recorded lower absolute heart rate responses during and after the stressor for every trial. Relative heart rate responses during the stressor and recovery were similar for both groups. There was also no difference between groups in T-wave response during or after the stressor. These data suggest that absolute heart rate response during and after repeated exposure to a psychological stressor is lower for aerobically trained individuals.

Effects of acute exercise on cardiovascular reactivity

Although exercise may modulate cardiovascular reactivity to stress, its acute effects have not been studied extensively. The purpose of this study was to examine over time the acute effects of different durations of aerobic exercise on cardiovascular reactivity to stressors. Twenty-four sedentary men underwent minimal exercise, 1 or 2 hr of stationary cycling at 55% VO2max. Heart rate, blood pressure, and blood catecholamines were measured during cold pressor, Stroop, and public speech tasks 1, 3, and 24 hr after exercise. One or two hours of exercise attenuated blood pressure responses to stress. The attenuation was evident 3 hr following exercise and was most apparent on the cold pressor task. These effects were independent of epinephrine level and stress appraisal. The role of central sympathetic processes in the effects of exercise and methodologic implications are discussed.

T-wave amplitude utility revisited: some physiological and psychophysiological considerations

The last decade has seen some quite polemicized discussions concerning the utility of T-wave amplitude as a psychophysiological measure, but more recent reports indicate that we are now moving into a more empirically oriented and analytic examination of this topic. Such a report is one by Contrada et al. (1989), who manipulated sympathetic (beta-adrenergic) influences both pharmacologically and behaviorally, and whose main conclusion was that their results "support the hypothesis that T-wave is significantly affected by beta-sympathetic influence on the heart". However, we question their other conclusion that "a nonspecific effect of heart rate change on T-wave amplitude would also account for these results", and also suggest that their discussion of the "implications for the utility of T-wave amplitude in psychophysiological research" bears further consideration. In particular, for psychophysiologists, of fundamental importance is the distinction between T-wave amplitude's utility as a physiological index and its utility as a psychophysiological index. Concerning the former issue, we consider: (a) the alpha/beta adrenergic distinction, (b) inappropriate T-wave amplitude augmentation effects to sympathomimetic stimulation, (c) the nonspecific-response-to-tachycardia argument, and (d) the view of pulse transit time as a criterial standard, rather than as a candidate index. Regarding the issue of psychophysiological index utility, we consider: (a) dependent-variable sensitivity, drawing a further distinction between reactive and specific sensitivity, and (b) independent-variable-manipulation effectiveness.

Reactivity to written mental arithmetic: effects of exercise lay-off and habituation

The present study examined (i) the effects of exercise lay-off on heart rate (HR) and subjective response to mental stress in 24 individuals highly committed to exercise, and (ii) psychophysiological reactivity to a challenging written mental arithmetic with subjectively controlled difficulty level. Subjects were tested on two occasions one week apart. Exercise withdrawal did not influence psychophysiological stress response. Second exposure to the mental arithmetic resulted in significantly lower HR response, due to habituation; higher pretask resting HR, due to anticipation of performance; and later onset in HR recovery. No changes in task performance and subjective measures were observed from session one to session two, indicating that habituation is rather a physiological than behavioral phenomenon. While these findings do not strengthen the link between exercise and stress response, they demonstrate the significant mediatory roles of habituation and anticipation in laboratory studies employing a test-retest design.

Effect of a six-month aerobic exercise training program on cardiovascular responsivity in healthy middle-aged adults

The purpose of this study was to determine the effects of a six month aerobic exercise training regimen on cardiovascular responsivity to mental arithmetic in healthy middle-aged men and women. Subjects were randomly assigned to a moderate intensity exercise intervention or to an assessment-only control group. Before and after the intervention subjects' heart rates and blood pressures were measured doing a mental arithmetic task (N = 83). Other physiological and psychosocial measures included the Type A structured interview and a maximal exercise treadmill test. Validated adherence to the exercise regimen exceeded 75% and there were significant increases in aerobic capacity in those subjects receiving exercise training. Exercise did not significantly reduce cardiovascular responsivity to the stress task. Type A behavior did not interact with reactivity across exercisers or controls nor was it significantly correlated with adherence. The results are discussed with respect to factors that have been previously reported to potentially influence the exercise/reactivity relationship.

Aerobic fitness, physical activity, and psychophysiological reactions to mental tasks

The association between aerobic fitness, exercise, and psychophysiological reactivity was assessed in cross-sectional and prospective analyses. Seventy-five healthy but sedentary adults carried out a sub-maximal exercise test and easy and difficult problem solving tasks. Blood pressure, heart rate, skin conductance level, respiration rate, tidal volume, and oxygen consumption were monitored and additional heart rate was also computed. Differences between relatively fit and unfit individuals were found in respiration rate during tasks and in skin conductance level during post-task recovery periods, with a tendency toward diminished heart rate reactivity in fitter people. Subjects were subsequently allocated to four conditions: high intensity aerobic training, moderate intensity aerobic training, an undemanding strength and flexibility program (designed as an attention-placebo condition), and waiting list control. Training programs were conducted over a 10-week period, and were followed by a second laboratory session. Appropriate changes in aerobic performance over the training period were observed in the 12-min run/walk test. There were no important modifications in psychophysiological stress reactions associated with the different experimental conditions. These results are discussed in relation to the literature concerning the effects of fitness and physical activity on physiological response patterns.

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.

On approaches to explaining cardiovascular reactivity: toward explanations that explain

The control-system mode of analysis proposed by Pavloski for cardiovascular reactivity phenomena is a purposive or teleological form of explanation, because the explicans has purpose as the central term. The problem with such explanations is that they are circular and empty, providing only a rhetorical feeling of understanding, and absence of strong-inference research. The S-O-R approach, which Pavlovski opposes, provides at least the potential for non-circular explanations, provided that the O-related explanatory constructs are specified in normal cause-effect terms so that, in another context, the explicans can also serve as an explicandum, and vice-versa. Pavloski may be right in suggesting that the evidence requires a feedback, "control-system" construct to account for cardiovascular reactivity phenomena (although he is far from having proved this in his paper), but such a view would need to be supplemented by (non-purposive) control-system explanations that really explain in the logical rather than the merely rhetorical sense of that term.

Aerobic fitness and the physiological stress response: a critical evaluation

Aerobically fit persons need less sympathetic activation to perform the same absolute workload than less fit persons. This led to the idea that aerobic fitness might reduce the physiological activation during psychological stress as well. Several experiments showed inconsistent results with regard to this supposed effect of fitness. The comparability of the results is hampered by the differences in operationalization of aerobic fitness and by the confusion of the terms aerobic fitness, training and habitual physical exercise. The expectancy of an effect of fitness on the physiological stress response is based on the assumption that this response resembles the response to exercise. The tenability of this assumption was examined for cardiac, vascular and hormonal responses respectively. It was concluded that the two types of responses only superficially have similarity. So a simple analogy between the stress and the exercise response does not allow a reliable prediction concerning the effect of fitness on the stress response. There are however other reasons to expect an effect. Especially the effect of fitness on adrenoceptor sensitivity suggests that the most important effect of fitness might be found in the vascular part of the stress response. It is argued that the measurement of complete response patterns, instead of isolated parameters, is a prerequisite for progress in this field. Future studies should address the question what the relative contribution of psychological and physiological factors is to the effect of fitness on the physiological stress response.