The purpose of this study is to investigate the relationship between oral contraceptive use and the musculo-tendinous stiffness of the knee flexors. Twenty-three female participants and ten male participants (control group) ranging in age from 20 - 30 years. A uniaxial accelerometer was used to assess stiffness based on the exponential decay of the damped oscillation. Female groups had estradiol and 17 a-OH progesterone levels tested. At 30% of MVC, the Ortho-Tri Cyclen group, the Other OC group and women not using OC's had a mean stiffness of 249.3+94.5, 274.1+79.1 and 216.0+43.3 Nm/rad respectively and at 50% of MVC values of 290.2+70.7, 326.7+78.9 and 267.9+52.6 Nm/rad respectively. No significant difference in stiffness was found. Also no correlation was found between estradiol and stiffness. These results indicate that there was no significance between knee stiffness and oral contraceptives within the female groups. / School of Physical Education, Sport, and Exercise Science