Circadian effects on the acute responses of salivary cortisol and IgA in well trained swimmers

Objective: To examine whether time of day significantly affects salivary cortisol and IgA levels before
and after submaximal swimming.
Methods: Fourteen male competitive swimmers (mean (SD) age 18 (3.2) years) volunteered to participate
in the study. In a fully randomised, cross over design, each subject performed 5 ´ 400 m front
crawl at 85 (1.2)% of their seasonal best time (277 (16) seconds), with one minute rest between each
400 m, at 0600 and 1800 hours on two separate days. Timed, unstimulated saliva samples were collected
before and after exercise. Saliva samples were analysed for cortisol and IgA by
radioimmunoassay and single radial immunodiffusion respectively.
Results: Significant time of day effects (am and pm respectively) were observed in IgA concentration
(0.396 (0.179) v 0.322 (0.105) mg/ml, p<0.05), IgA secretory rate (0.109 (0.081) v 0.144 (0.083)
mg/min, p<0.01), and saliva flow rate (0.31 (0.23) v 0.46 (0.22) ml/min, p<0.001) before exercise
(all values mean (SD)). Differences in cortisol levels before exercise (1.09 (0.56) v 0.67 (0.94) μg/dl)
approached significance (p = 0.059). The exercise protocol did not significantly affect IgA concentration
and secretory rate (p>0.05) but, in comparison with values before exercise, caused significant
alterations in cortisol (p<0.01) and saliva flow rate (p<0.01). There was no significant interaction effect
of time of day by exercise on any salivary variables measured (p>0.05). However, most of the values
of the salivary variables before exercise were significantly inversely related to their exercise induced
response (p<0.05).
Conclusion: These results suggest a significant circadian variation in the variables measured before
exercise, without showing a significant effect on their acute responses to exercise.