Originally Posted by
DrIsotope
I would have to think less energy, because we're already so inefficient. For me, a 40-mile ride @ 90ºF I might intake +50oz of water, while the same ride @ 50º might be 8oz of water. I'm producing the same amount of waste heat both days, but on the colder day I can actually use that heat-- I don't need to sweat buckets to accommodate it. At least to a point. Below 30ºF I always feel like output is way down-- my body just doesn't like it that cold. Once the hands and feet get chilled through, I feel like I'm just trudging along.
This is a good answer. According to my understanding, the physiological processes involved in body cooling require energy and they can be dialed back when exercising in the cold. Active physiological heating consists of shivering and brown fat metabolism, but they don’t kick in until core temp falls to the shivering point, and no one, other than outdoor workers and street people, likely has enough brown fat to make a big difference. Up until that point, all the body does is vasoconstriction, which reduces the volume of the circulation, making it more efficient—the opposite of what happens in the heat. People have pointed this out up thread.
I do think about the viscosity of heavy tights and the weight of my Lake winter boots. I think I can feel that. The air density thing is also interesting.