Ischemic but not thermal pain sensitivity varies across the menstrual cycle

Findings from both animal and human research suggest that pain sensitivity changes across the menstrual cycle; however, among humans the nature of these menstrual cycle effects remains unclear. The present study used a repeated-measures design to evaluate changes in thermal and ischemic pain responses during three phases of the menstrual cycle, midfollicular (postmenstrual), ovulatory, and mid-to-late luteal (premenstrual), in 11 healthy women. The cycle phase during which subjects began their participation was determined randomly. Plasma levels of estrogen, progesterone, luteinizing hormone (LH), testosterone, and beta-endorphin were determined at each experimental session. Participants also completed a daily diary of physical and emotional symptoms for two complete menstrual cycles before the experimental sessions. The results indicated that women showed less ischemic pain sensitivity during the midfollicular compared with the ovulatory and mid-to-late luteal phases, but thermal pain responses did not vary significantly across menstrual cycle phases. Physical and emotional symptoms were minimal and did not change significantly across the menstrual cycle. These findings indicate greater ischemic but not thermal pain sensitivity among women after the midcycle LH surge. The practical relevance and potential mechanisms of these findings are discussed.