That's an excellent question. For me, it is very difficult to play when my hands are cold. They get stiff and rigid and the compositions just don't flow out like I would like them too. Before practicing and performing, I run my hands under hot water. I believe that this loosens the muscles and allows them to move and flow more evenly. Glenn Gould, a famous Bach performer, soaked his hands in a bowl of warm water before he went on stage. However, what do you do when there's nowhere to wash your hands? This is when I put on a pair of extremely heavy and thickly insulated mittens. It has the same effect, just without the physical water. Hope this helps!