Effects of circulating estradiol on exercise-induced creatine kinase activity

The present investigation sought to determine the effects of circulating estradiol (E2) and oral contraceptive use on serum creatine kinase (CK) activity following acute eccentric exercise. Ten college-aged female subjects were grouped according to their use (OBC, N=5) or non-use (NOBC, N=5) of an oral contraceptive. Both groups performed strenuous eccentric muscle actions (5 sets with 10 repetitions/set; ≥100% of concentric 1RM) during the menstrual cycle phase corresponding to low E2 concentrations. The OBC group had significantly lower E2 concentrations than the NOBC group (11.6 versus 27.2 pg/mL, respectively; p<0.01) prior to exercise. The results indicated that the OBC group (lower E2) had significantly higher CK activity at 48 and 72 hr post-exercise when compared to baseline CK activity (p<0.05). Although the NOBC (higher E2) group showed a slight increase in CK activity at 24, 48 and 72 hr post-exercise, values were not significantly different from pre-exercise. Perceived soreness values were generally dissociated from CK activity, but demonstrated a similar post-exercise response between groups. The results indicate that pre-exercise concentrations of circulating estradiol can affect serum CK activity following damaging eccentric exercise.