The female orgasm: pelvic contractions.
Eleven nulliparous women manually self-stimulated to orgasm, each on three separate occasions. Pelvic contraction pressure was measured by an anal probe and a vaginal probe simultaneously. Near the perceived start of orgasm, a series of regular contractions began in nine of the women. Anal and vaginal contraction waveforms were synchronized with each other, and the same number of orgasmic contractions occurred in each lumen. Anal pressure had a higher resting baseline and greater amplitude contractions than vaginal pressure. The perceived start of orgasm did not correspond precisely with the onset of regular contractions. Mean intercontraction intervals increased linearly at an increment of about 0.1 second through the series of regular contractions. Amplitudes of contraction pressure waveforms, representing pelvic muscular force, were initially low, increased through the first half of the regular series, and then decreased. Area and net area of the pressure waveforms, reflecting pelvic muscular exertion (force x time), increased during the regular orgasmic contractions. Three of the women's orgasms consistently included only a series of regular contractions (orgasm type I). For six other women, orgasms consistently continued beyond the regular series with additional irregular contractions (orgasm type II). Types I and II had been identified previously in men. Two women had no regular contractions during reported orgasms. This pattern, type IV, had not been recorded in men. Women of different types showed marked differences in orgasm duration and number of contractions. Identification of these types in subjects is important for meaningful comparison of contraction parameters in different studies.