1. The effect of the different phases of the menstrual cycle on skeletal muscle strength, contractile properties and fatiguability was investigated in ten young, healthy females.Results were compared with a similar group on the combined (non-phasic) oral contraceptive pill (OC). Cycle phases were divided into the early and mid-follicular, midcycle (ovulatory) and mid-and late luteal. Cycle phases were estimated from the first day of the menstrual bleed. 2. Subjects were studied weekly through two complete cycles. Previous studies of muscular performance during the menstrual cycle have concentrated mainly on changes in endurance performance, rather than strength, and have usually compared the early follicular and luteal phases (for review see Lebrun, 1994). Those studies which have looked at explosive power events have mainly measured performance levels, which are influenced by many variables other than muscle strength or power output. One study investigated the changes in handgrip strength and standing long jumps during the menstrual, ovulatory and luteal phases of the cycle (Davies, Elfors & Jamieson, 1991). The only significant difference found was a stronger handgrip strength during the menstrual phase, which the authors attributed to the lower oestrogen and progesterone levels. These results therefore conflict with those of Phillips et al.(1993a).Despite the high level of interest in the effect of the menstrual cycle on athletic performance and fitness, there remains considerable controversy in the literature. The purpose of this study was to investigate the effect of the menstrual cycle phase on simple tests of muscle strength in large muscle groups which are important in many sporting and everyday tasks (quadriceps and handgrip). In order to