Why is climbing out of the saddle so tough for me? It really wears me out when I do it, but I do enjoy it. I'm a recreational rider, so it matters not, aside from the fact that I'd like to do it more for my own enjoyment.

I'm a heavy guy at 104 kg/230 lb. Yeah, yeah, I'm trying to get back into shape. So is my difficulty with climbing out of the saddle simply a function of the load I'm hauling? Is it easier if you're lighter?