Dynamic strength and work variations during three stages of the menstrual cycle.

The purpose of this article was to investigate the effects of three different phases of the menstrual cycle on dynamic strength and work performance of the knee flexors and extensors. Twenty-one women (18-36 years of age) were tested for dynamic strength and endurance on a Cybex II isokinetic dynamometer at speeds of 60, 180, and 240 degrees /sec. Each subject was tested within 24 hours from the onset of the menses, at the time of ovulation, and during the luteal phase. Strength was determined by peak torque values of knee flexion and extension at the three speeds. Flexion and extension endurance ratios and a work ratio was determined at a speed of 240 degrees /sec. ANOVA failed to show any significant differences among the strength variables during the three phases of the menstrual cycle. The endurance ratios indicated that peak torque values were less than two-thirds of original strength at the end of 20 repetitions. Flexors fatigued slightly less than extensors. There were no significant differences in work ratios among the three phases. Thus it was concluded that the active woman with a normal cycle should experience no discernible change in strength and work performance as a result of cycle changes.J Orthop Sports Phys Ther 1988;10(4):113-116.