Are you talking A) feet pressed soles flat against the side (legs spread open) of the stipes, or B) the sides of the feet against the stipes and the nail driven in from the side of the foot? (Damn, it sounds like I'm asking if this is an African or European Swallow, sorry.) Because if the nail is driven from the side through the heel or ankle, it would rotate on the nail every time you pushed up.I wouldn't be so sure of that. I think a lot of it depends on how they've nailed the feet. If your feet at nailed either side I would imagine you'd have stability so you could push upwards..... Where as, if your feet are nailed one over the top of the other, your feet would pivot on the nail causing your feet to rotate inwards making harder to hold your weight on already mega agonised feet.
Feet nailed to either side of the post would be the lesser of the two.....
Trev
A)
B)