Thanks Admi.
One thing that those visual aids and the ones at the top have hammered home hard to me is the point (ouch!!) that the nails driven into me, especially in my feet (whether vertically through the instep or laterally through my ankle) will be in contact with my bones, rubbing against them, pushing them, even cracking them. As anyone who's experienced a fracture or severe impact on a bone (as all of us who've been whipped know well), that's where the main nerves run, that's where pain is most horrendous.
So if I'm pushing down on my nail feet to try to ease the strain on my shoulders, the agony will be hideous, the nail (whether 1 or 2) forcing against the tiny bones like a metal wedge. Giving up and letting my wrists take the weight will be marginally better, but even there the pressure against the carpal joint, gradually forcing it open, as well as the strain on my upper arms, shoulders and chest, will be unbearable.
I doubt whether I or any averagely healthy youngish woman would be able to survive that agony for more than a matter of minutes, before at least losing consciousness and probably dying under the shock. Fitting a sedile after you've enjoyed 10 - 20 minutes of my struggling would be essential if you want me to survive for hours or even days.
I've sometimes thought about the alternative of not nailing or restraining the feet at all. If I were nailed by my wrists, and supported (hanging below the level where my arms are stretched to strain-pain point) by an uncomfortable sedile with a sturdy 9"/20cm cornu in my vagina, I'd be firmly held in a very distressing and humiliating position. My legs could kick freely, I'd even struggle to wrap them around the stipes and lift myself to ease the strain, and you could hammer in a large nail where I can just reach it with my big toe to press down on for slight, temporary relief to my arms, but of course I'd have no chance of escaping that spike penetrating right into my womb. Crucifixion in this way would be less agonisingly painful, but I'd survive a good deal longer, probably (given water) several days, and my helplessness would make for enjoyable viewing.