Check this bit of journalism witnessing firsthand the products of R&D ongoing at DARPA (Defense Advanced Research Projects Agency), in Virginia.
All it takes is a chilled metal sphere, your hand tightly gripping the sphere, and a vacuum around your hand, and not only won’t your body overheat, but you’ll be able to do nearly 1000 consecutive pushups.
I’m not kidding. Apparently by pulling blood to the surface of the skin and either heating or cooling the hands, your body can recirculate either cooled or heated blood and counteract the effects of an overheated–or overcooled and hypothermic–body. The effect can prolong the body’s endurance when it’s in extremis, whether cold or hot.
Looking forward to using these things on the battlefield.