Serum creatine kinase activity, oral contraception use, and exertional rhabdomyolysis

Abstract

2297 Animal studies have shown that estrogen attenuates creatine kinase (CK) release from skeletal muscle damaged via strenuous exercise, likely due to the membrane stabilization properties of estrogen. To examine this effect in humans, two previous studies compared blood CK activity after exercise in oral contraception users and nonusers and found no significant difference between the groups. However, these studies used small sample sizes and, due to the high variability in the CK response, may not have had sufficient statistical power to detect differences. PURPOSE: We examined post-exercise changes in serum CK in a large group of women who participated in a clinical trial, with the hypothesis that women taking oral contraceptives (OC) would show a blunted CK response to damage-inducing exercise due to the chronic elevation of estrogen induced by OC use. METHODS: Subjects were grouped into non-users (NonOC, N= 59) and OC users (N=37). Subjects performed a bout of 50 eccentric contractions of the elbow flexors. Maximal isometric strength (MVC) was assessed before and immediately following the exercise. Blood samples were taken pre and 4 d post-exercise and analyzed for CK activity. Strength loss and serum CK levels were evaluated using repeated measures ANOVA. RESULTS: The percent MVC loss immediately post-exercise (mean (SE)) was 57 (2.5) and 57 (3.2) for NonOC and OC, respectively. The CK activity at 4 d post-exercise for NonOC and OC was 5790 (807) and 5569 (1126) U/L. There were no significant differences between groups in MVC loss or CK. Pearson correlation between CK and percent immediate MVC loss was r= −0.5 (p<.01) for all subjects and r= −0.46 (p<.01) and r= −0.53 (p<.01) for NonOC and OC users, respectively. CONCLUSION: CK activity 4 d after eccentric exercise was strongly related to strength loss induced by the exercise but did not differ significantly between OC and Non OC users.