If you're working up a sweat, I'd hazard a guess that you're doing it wrong. Working up a sweat in winter will kill you, and native americans used snowshoes regularly for months on end, in temperatures of 40 below, year after year, until the invention of the snowmobile.

Disclaimer: I've only gone snowshoeing once, in the Canadian Armed Forces reserves for a winter warfare weekend exercise, but we travelled a considerable distance and I don't remember being winded or exhausted; in fact, it was the most fun I ever had on a military exercise.

Backpacking on snowshoes doesn't make a lot of sense to me; far better to get yourself a proper sled for towing and put your gear on that, which is how the Canadian Army and native americans, at least, do it.

My guess is, you're carrying all your winter survival gear in a humongous backpack, weighing twice as much as it does in summer, and wearing oversize snowshoes to compensate for the added weight. Ditch the backpack; buy yourself a couple of cheap children's sleds, made out of molded plastic, rig up a handle (so they don't run into you when you're going downhill), tie your backpacks onto them and haul your gear behind you.