The effect of exercise on serum and salivary cortisol in male children.

The purpose of this study was to examine serum and salivary cortisol responses to cycling exercise in male children, 10.6 +/- 0.2 yr (mean +/- SE). Each child performed a graded exercise test on a cycle ergometer to determine VO2max. On a separate day, a 30-min bout of exercise at 70% of VO2max was performed. Blood, obtained from a venous catheter, and saliva samples were collected at rest, at 15 and 30 min of exercise, and 15 min post-exercise. The mean serum cortisol level at 15 min (7.94 +/- 1.43 micrograms.dl-1) and 30 min (8.72 +/- 1.77 micrograms.dl-1) of exercise and at 15 min post-exercise (8.21 +/- 1.59 micrograms.dl-1) were significantly greater than rest (5.54 +/- 0.86 micrograms.dl-1). The increase in salivary cortisol levels over time approached (P = 0.08), but did not reach significance. However, effect size analyses indicated that the increase in salivary cortisol at 30 min of exercise (0.64) and 15 min post-exercise (0.62) was similar to the change in serum cortisol at these same two time points (0.72 and 0.66, respectively). Serum and salivary cortisol were correlated (P < 0.05) at 15 min of exercise (r = 0.77), 30 min of exercise (r = 0.90), and 15 min post-exercise (r = 0.84), but not at rest (r = 0.46). In conclusion, 30 min of submaximal exercise at 70% of VO2max significantly increased serum cortisol level; and salivary and serum cortisol are correlated during and after exercise.