The interrelationships among sex hormone concentrations, motoneuron excitability, and anterior tibial displacement in women and men.

CONTEXT: Sex hormone fluctuations have been implicated as a contributing factor to the high rates of noncontact injury to the anterior cruciate ligament in females.

OBJECTIVE: To determine the strength of the relationships among variables of sex hormone concentrations, motoneuron excitability, and anterior tibial displacement (ATD) in women and men and to determine if these relationships differ between the sexes.

DESIGN: Cohort study.

SETTING: Sports medicine laboratory.

PATIENTS OR OTHER PARTICIPANTS: Twenty-eight regularly menstruating women (age = 22.4 +/- 3.4 years) and 15 men (age = 22.3 +/- 3.7 years) participated in the study.

INTERVENTION(S): Fluctuations in sex hormones were determined for the participants. Female participants were tested every other day of their menstrual cycles, whereas male participants were tested every fourth day during the 28-day period.

MAIN OUTCOME MEASURE(S): We measured Hoffmann reflexes (maximum Hoffmann reflex [H(max)] to maximum M-wave [M(max)] ratio in the soleus), ATD under a 134-N load, and saliva concentrations of estrogen and progesterone. The independent variable was sex. Pearson product moment correlation coefficients were calculated for each participant by pairing measurements made on the same day. Two-tailed independent-samples t tests were used to determine the difference between the male and female correlations for each variable.

RESULTS: Over the course of the study, the relationships between H(max)ratioM(max) and estrogen, H(max)ratioM(max) and progesterone, ATD and estrogen, and ATD and progesterone were not different between the sexes. However, the relationship between ATD and progesterone was different between the sexes (P = .036).

CONCLUSIONS: The observed correlations did not support our hypothesis that the relationships between sex hormone levels and reflex activity or between sex hormone levels and ATD would be different for women compared with men. If sex hormone concentrations significantly contribute to anterior cruciate ligament ruptures because of changes in laxity or in motoneuron excitability, their mechanism of action is likely multifactorial and complex.