As the manufacturers of motorcycles know, having cold hands leads to a lack of concentration and often results in accidents. I was watching some people playing hockey in very cold weather when the following, related, idea occurred to me.
The shaft of each winter sports stick (including icehockey, hiking, skiing, shinty etc) could be filled with a long, thin tube full of heat pad crystals. This tube would be extracted, pre-game, boiled and reinserted, providing at least one half’s worth of handwarming (reheatable at half time if necessary).
The volume and placement of the tube could be tuned, for a given size of stick, to maintain the normal sweet spot (centre of percussion) in ballgames, without affecting the held surfaces or the freedom to change grip.