Neuromuscular performance and balance during the menstrual cycle and the influence of premenstrual symptoms

Sammanfattning: Several studies have demonstrated a higher incidence of sports related knee injuries among female athletes compared to their male counterparts regardless of exposure time and activity level. Different intrinsic and extrinsic factors have been proposed as risk factors in women. The hormonal variation during the menstrual cycle has been suggested as one of the intrinsic factors and an association between sport injuries in female athletes and the menstrual cycle has been reported. An increased injury rate has been observed during the premenstrual and menstrual phase, whereas one author reported a higher incidence during the ovulatory phase. It has been suggested that impaired neuromuscular function due to the specific hormonal influence of the menstrual cycle contributes to the association between sport injuries and different phases of the menstrual cycle. Furthermore, women with premenstrual symptoms (PMS) have been shown to be at greater risk of injury compared to women without PMS. The overall aim of this work was to explore if and how neuromuscular performance and balance vary across three well defined and hormonally confirmed phases of the menstrual cycle in moderately active women and to study if PMS can affect performance. Muscle strength and endurance, knee joint kinesthesia, neuromuscular coordination and postural control were measured in the early follicular phase (FP), the ovulatory phase (OP) and the mid luteal phase (LP) of the menstrual cycle. Menstrual cycle phases were determined by analysis of sex hormone levels in serum and ovulation was detected by the luteinising hormone surge in urine. A prospective rating of PMS was used to divide the subjects into two groups, one with PMS and one without. No significant variations in muscle strength or muscle endurance during the menstrual cycle were detected. An impaired knee joint kinesthesia was detected in the LP and women with PMS showed an overall greater threshold for detection of passive movements than women without PMS. Neuromuscular coordination was significantly improved in the OP compared to the other phases. A significantly altered postural control was detected in the LP in the PMS group, but no differences were shown between phases in the non-PMS group. There was no significant difference in hormone levels between the PMS group and the non-PMS group and there were no correlations between hormone levels and the variables tested. The results of this thesis demonstrate a significant variation in knee joint kinesthesia, neuromuscular coordination and postural control during the menstrual cycle, while no differences in muscle strength or endurance were observed. Impaired neuromuscular performance and balance may contribute to the increased incidence of sports injuries in female athletes. Further studies are needed to clarify the precise mechanisms for menstrual cycle related variation in neuromuscular performance and postural control.