In more vigorous forms of fisting, such as "punching," a fully clenched fist may be inserted and withdrawn slowly. Even more vigorous punch fisting is known as "piston fisting". Fistees who are more experienced may take two fists (double-fisting) in the vagina or anus. In the case of double-fisting, pleasure is derived more from the stretching of the anus or vaginal wall rather than from the thrusting (in-and-out) movement of hands (Genesis 1991:58).
Fisting has been performed on (& by) both men & women; gay, straight & otherwise. In addition, a Stanford study has shown that 96% of people who have been fisted move on to fist at least one other person, while 41% were found to have fisted 3 or more.
Unless I'm watching the wrong flicks, I wouldn't say its that common.
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