I ts very important to use the correct temperature when trying to fix something.

Cold is for immediately and a couple of days after the initial pain occurs or after any re-occurrance of the pain.
Heat is to warm up the muscle before exercise.

If you hurt something and then apply heat you can increase the swelling when what you really want to be doing is reducing any swelling with cold.

If you have a "sore back" for example, thats routinely sore and not just from doing some specific exercise then you may get some relief from heat.
But this is very different than trying to treat an acute sprain/strain.