Daily timing of salivary cortisol responses and aerobic performance in lean and obese active females

Abstract

The main aim of the present study was to study the effects of morning and afternoon physical activities on cortisol responses in obese and lean women. Twenty women volunteered to participate in this study. Subjects were divided into an obese group (BMI =29.1 kg/m2) and a lean group (BMI =19 kg/m2). All subjects participated in an exercise program consisting of treadmill running at 65±2 % VO2max until exhaustion. In order to study effects of circadian rhythm, exercise was performed at a similar intensity and in similar environmental conditions at both 8:00 AM and 4:00 PM. Saliva specimens were collected at rest 20 minutes before activity and then immediately after the exercise in both morning and afternoon sessions. Morning and afternoon exercise resulted in a significant increase in salivary cortisol concentrations compared to basal levels in both lean and obese women (p<0.05), though the change in cortisol concentrations were higher in lean. The aerobic function of lean and obese women in the morning and afternoon showed a significant increase of 13.8 % and 5.9 %; respectively, with lean being consistently higher than obese. In conclusion, the stress response to exercise is related to circadian rhythm and individual's body weight. Based on the results of this study, it is suggested that overweight women perform exercises in the afternoon to minimize the stress response for the exercise volume performed.