The relationship between leisure-time physical activity and stress on workdays with special reference to heart rate variability analyses

The purpose of this study was to investigate how physical activity (PA), cardio- respiratory fitness, and body composition are associated with objective heart rate variability (HRV)-based indicators of stress and recovery on workdays. Additionally, the association of subjective self-reported stress with HRV-based stress was investigated. Samples of 81 healthy men (age 26–40 years), and 16 275 Finnish employees (6863 men and 9412 women; age 18–65 years) were assessed in the cross-sectional analyses. A sample of 221 overweight psychologically distressed individuals (36 men and 185 women; age 26–60 years) was examined in both cross-sectional and longitudinal analyses. HRV-based stress and recovery were determined from the beat-to-beat R–R interval recordings mainly over 2 workdays in a real-life setting. The Perceived Stress Scale was used to assess subjective stress. The level of PA was evaluated using both subjective (validated questionnaire/interview) and objective (real-life R-R interval recording) methods. Cardiorespiratory fitness and body fat percentage were determined under laboratory conditions. Additionally, body mass index (BMI) (kg/m2) was used as a measure of body composition. The results showed a positive association of subjective stress with HRV- based stress. Higher PA, cardiorespiratory fitness, and favorable body composition were associated with a lower level of HRV-based stress. Cardiorespiratory fitness and favorable body composition were associated with better recovery during sleep. A higher initial level of HRV-based stress predicted a weaker decline, whereas a higher initial level of PA and HRV-based recovery predicted a larger decline in subjective stress during a 9-month study period among psychologically distressed and overweight individuals. The results indicate that there is an association between subjective and objective HRV-based stress measured in real-life. However, these two dimensions of stress react differently over the long term. Additionally, the results support the beneficial effects of PA on HRV-based stress