I've worked in all types of weather. Some of the work was heavy labor in different conditions, but none were as brutal as that in cold weather. I don't think we're really designed for it, and the worst of fatigue I ever experienced was after working a long day in cold weather. Summer can be exhausting, but the cold takes more, and the constant cold takes much more to endure.
I'm glad I don't have to spend long days in the cold any longer. Truthfully, I don't think I have the stamina any more.