I've got chronic sciatica, and multiple compressed or ruptured discs as well as severed nerves, and kneeling for me is absolute torture because it forces the lower back to curve, further loading up on the injuries, what works for me is my kneeling thwart is lowered and angled so I can use it for a toe bar, essentially locking me in place.I kneel about half the time because it takes all the pressure off my lower back. If anyone has compressed discs or problems with sciatica, then kneeling is the perfect solution. My ability to be in a boat for a long time is a function of being able to change position frequently. Whenever I kneel in a canoe it reminds me of my father, who didn't canoe, but was able to spend extended periods kneeling on the ground, thigh and shin folded flat, with feet folded over each other. For me it comes naturally because I've done it all my life, but I imagine if you haven't it takes some getting used to over time. Bucking firewood with a chainsaw on the ground is easy for me, but most people struggle.