Attenuation of stress-induced hypertension by exercise independent of training effects: an animal model

Changes in cortisol release and heart rate and heart rate variability during the initial training of 3-year-old sport horses

Based on cortisol release, a variety of situations to which domestic horses are exposed have been classified as stressors but studies on the stress during equestrian training are limited. In the present study, Warmblood stallions (n=9) and mares (n=7) were followed through a 9 respective 12-week initial training program in order to determine potentially stressful training steps. Salivary cortisol concentrations, beat-to-beat (RR) interval and heart rate variability (HRV) were determined. The HRV variables standard deviation of the RR interval (SDRR), RMSSD (root mean square of successive RR differences) and the geometric means standard deviation 1 (SD1) and 2 (SD2) were calculated. Nearly each training unit was associated with an increase in salivary cortisol concentrations (p<0.01). Cortisol release varied between training units and occasionally was more pronounced in mares than in stallions (p<0.05). The RR interval decreased slightly in response to lunging before mounting of the rider. A pronounced decrease occurred when the rider was mounting, but before the horse showed physical activity (p<0.001). The HRV variables SDRR, RMSSD and SD1 decreased in response to training and lowest values were reached during mounting of a rider (p<0.001). Thereafter RR interval and HRV variables increased again. In contrast, SD2 increased with the beginning of lunging (p<0.05) and no changes in response to mounting were detectable. In conclusion, initial training is a stressor for horses. The most pronounced reaction occurred in response to mounting by a rider, a situation resembling a potentially lethal threat under natural conditions.

Effects of exercise on Pavlovian fear conditioning

Exercise promotes multiple changes in hippocampal morphology and should, as a result, alter behavioral function. The present experiment investigated the effect of exercise on learning using contextual and auditory Pavlovian fear conditioning. Rats remained inactive or voluntarily exercised (VX) for 30 days, after which they received auditory-cued fear conditioning. Twenty-four hours later, rats were tested for learning of the contextual and auditory conditional responses. No differences in freezing behavior to the discrete auditory cue were observed during the training or testing sessions. However, VX rats did freeze significantly more compared to controls when tested in the training context 24 hr after exposure to shock. The enhancement of contextual fear conditioning provides further evidence that exercise alters hippocampal function and learning.

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.

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.

The effects of exercise training on mental well-being in the normal population: a controlled trial

This study was designed to compare the effects of two aerobic training programmes of differing intensities on mood and mental well-being with those of a credible attention-placebo condition. One hundred and nine sedentary adult volunteers from the local population were assigned to four conditions: high intensity aerobic training, moderate intensity aerobic training, attention-placebo and waiting list. Training was carried out over a 10 week period. Subjects were assessed before and after training with psychological measures and the 12 min walk-run test, and follow-up evaluations were undertaken after 3 months. Ninety-four subjects began the programme and the adherence rate averaged 80%, with no significant differences in number of drop-outs between conditions. Appropriate changes in estimated maximum oxygen consumption were observed in the three active conditions with the 12 min walk-run test. Psychological benefits were seen with the moderate exercise condition but not in the high exercise or attention-placebo conditions. These effects were manifest immediately after training on measures of tension/anxiety and confusion, and at follow-up on measures of perceived coping ability. The mechanisms underlying this pattern of results are discussed and the relative importance for health of vigorous activity and physical fitness is considered.