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

Abstract

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.

The effect of mental stress on heart rate variability and blood pressure during computer work

“…The main finding of this study, that HRV indices of parasympathetic nervous activity are sensitive indicators of mental stress during computer work, are consistent with a number of other studies using either prolonged (Bernardi et al 2000;Miyake 1997;Pagani et al 1991) or short-term exposure to psychosocial stressors (de Geus et al 1990;Sloan et al 1991). The latter two studies suggested a withdrawal of vagal modulation of the heart during short-term stress.…”

Effects of mental workload on physiological and subjective responses during traffic density monitoring: A field study

“…Our results were consistent with the results of the above mentioned studies. The HRV indices of parasympathetic nervous system activity were sensitive indicators of MWL during traffic density monitoring; this main finding was consistent with a number of other studies using either prolonged (Miyake, 1997;Bernardi et al, 2000) or short-term exposure to psychosocial stressors (De Geus et al, 1990;Sloan et al, 1991). Ryu and Myung (2005) showed a clear correlation between the difficulty of the tracking task and HRV indices.…”

Physical training and the dynamics of the cardiac baroreflex: A comparison when blood pressure rises and falls

“…Another hypothesis to explain the beneficial effects of exercise is the reduction of cardiovascular reactivity and/or increased recovery from stress. It is postulated that the improvement of vagal tone could attenuate cardiovascular reactivity, compensating for the increases in sympathetic cardiac influences under stress (de Geus et al, 1990;Sakakibara and Hayano, 1995). Some studies have found that fitness level is associated with smaller reactivity effects on both the heart and the vessels (van Doornen and de Geus, 1989).…”