I feel it is incumbent on me (a person who actually knows anatomy) to say that none of the recent videos I saw posted in this thread show fisting being done in a manner that exemplifies skillful, deftly performed fisting that eases insertion to great depths. She did get in deeply, but in a very awkward and unskillful manner. She has ZERO knowledge of anatomy, and yes, I can blow my own horn and exclaim that I AM AN EXPERT on this topic. Being able to stick your hand up someone's ass does NOT mean you know anatomy.
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First of all whether the fister is right or left handed is NOT NOT NOT the reason to use either hand. The reason to select which hand to use when fisting somebody depends on which direction both of you are facing.
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Maybe this will help you go to the elbows and beyond or at least get in more easily. . . . .
If you, the receiver, are on your back and your wife is lying, sitting or standing between your legs, she should use her RIGHT hand to fist you. In that position, your descending colon will be on your wife's right side and will turn left into the receiver's transverse colon, which is what you want because her left wrist and arm won't be able to bend properly to go up your descending and into the transverse. Her left hand and wrist as it were, would be asked to bend backwards to follow the curves of the colon. Using her right hand in this position enables her elbow and wrist to bend in the necessary directions to get in very deeply.
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If you, the receiver, are lying on your stomach or are on all fours, and your wife is lying, sitting or standing between your legs essentially facing your buttocks, and both of you are essentially looking in the same direction, she should use her LEFT hand because that way her wrist and arm will be able to bend in the direction of the colon. Her left hand will enter the rectum, then sigmoid going superiorly into the descending colon, which in the receiver will then turn right into the transverse colon. The fister's LEFT hand will be able to make those bends very easily.
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If you only go in about a foot or less, it does not matter which hand you use--but for very deep insertions like the elbow and beyond, IT MATTERS.
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As an avocational tribologist, the use of J-Lube, X-Lube or K-Lube is best because it is water soluble and its lubricating ingredient, hydrated polyethylene oxide IS the most lubricious/slippery sexual lubricant on the market despite having to occasionally re-apply it or spray some water on the skin to keep it hydrated and slippery. We never liked crisco.