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What is the simplest way to get the center of mass of a human body when sitting? I'm especially interested in getting this when sitting in a chair, so this center of mass would include the chair. I'm trying to make an exercise device for myself that attaches to a lift that I installed on my ceiling. I use a wheelchair and don't get much movement other than pushing my wheelchair, so I'm hoping this will improve my health.

My intention is to have a bar stabilizing the chair, but I don't want a lot of torque/stress (axle) on the chair. You can think of the axle as the rod that might connect the inner gimbal of a gyroscope. But this will only rotate on one axis. I will simply be able to change my pitch with this chair hanging.

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    $\begingroup$ I might suggest that you try to design a system that allows you to tune the exact position of the stabilizing bar after building it. This would allow you to get it more fine-tuned than any estimation will give you, as well as allowing you keep it stable if you gain or lose weight or muscle mass. $\endgroup$ Nov 25, 2017 at 6:18

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The chair can be hanging from a self leveling short (say 6 inches vertically by 2 inches horizontally) metal strap on each side. these brackets are attached to your bar through a bolt and nut on top passing through a flange welded on the bar, providin approximately 5 inch hanging distance between the floor of the chair and its support hinge!

Anybody can adjust the balance when they sit on the chair and let the gravity swing and suspend the chair and its occupant to CG of the system while the bar is locked.Then they tighten the screws on the bracket and unlock the bar!

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This link should help:

https://www.faa.gov/data_research/research/med_humanfacs/oamtechreports/1960s/media/AM62-14.pdf

For a natural sitting position with hands in the lap, the center of gravity is about (from what I can make out from the text - it is not clear) 8 3/8" (21.3 cm) and 9 1/8" (23.2 cm) from the horizontal and vertical reference points, which I believe are taken to be the horizontal and vertical surfaces of the seat. This would put the centre of mass somewhere around the position of your navel.

Including a wheelchair in the centre of mass would shift it downward and rearward probably by a small amount - maybe somewhere closer to your lap, but it all would depend on your mass and the mass of your wheelchair, etc.

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