Formally known as an Exercise Induced Orgasm (EIO), a coregasm is an orgasm that is triggered by physical exercise or some other abdominal engaging activity.
Coregasms are actually relatively common amongst women, and those who are not orgasming may atleast be experiencing Exercise Induced Sexual Pleasure (EISP). A 2011 study coauthored by the fantastic Debbie Herbenick, examined the occurance of EIOs and EISPs in 530 women. The main findings were that a variety of different activies can lead to EIOs, including climbing, sit-ups and weight lifting. Importantly, women who had EIOs rarely had them in connection with sexual thoughts or fantasies, which has interesting implications for our understanding of female sexuality.
The majority of females in the study sample, noted that uncontrollably climaxing in a gym is actually a little embarassing. But if you would like to have a coregasm, science suggests the 'captain's chair'.