Fisting is a sexual activity. The fister puts his or her hand into the vagina or rectum. The fingers are then clenched into a fist or kept straight. Fisting may be done with or without a partner.
Fistees is another form of fisting. It is for the more experienced. It may take two fists. This is called double fisting. Double fisting pleasure depends more on stretching of the anus or vagina rather than thrusting with an in-and-out movement of the hands.[1]
Fisting can cause lacerations to the vagina, perineum, rectum, and/or colon. This may result in serious injury.[2] These lacerations may even lead to death.[3][4][5][6] Sexual activities that cause air to enter the vagina can lead to a fatal airclot. [source?] The risk is probably even higher during pregnancy.[7]
Risks
Fisting can cause cutting or tearing or of the vagina, perineum, rectum, and/or colon, resulting in serious injury[2] and even death.[3][4][5][6] In general, sexual activities that cause air to enter the vagina can lead to a fatal air clot, and the risk is probably even higher during pregnancy.[7]
Anal fisting carries risks of colorectal tearing; people doing it should use latex gloves and lubricant, and have a safeword, which they can say when they want it to stop immediately. The practice, along with the insertion of hard objects into the anus or the vagina has been significantly related to the traumatization of the vaginal or rectal mucosa in increasing the likelihood of infection, including Hepatitis B virus.[8]
Donovan B; Tindall B; Cooper D. Brachioproctic eroticism and transmission of retrovirus associated with acquired immune deficiency syndrome (AIDS). Genitourin Med. 1986 Dec;62(6):390-2.