Heat Wave Instant Hot Pack
Love this!  A simple push of a button causes a chemical reaction and the pack turns hot.  I believe it lasts for about 30 - 40 minutes, but enough time to loosen up those muscles.  Have to boil the packs in water to get it back to it's original state, but if you still need a hot pack, coming out of the boiling water should take care of that!  Highly recommend!
Rating: 5 stars