A small study suggests it may not matter which one you choose.
Researchers say that neither heat nor cold will do much to ease that pain - at least, not immediately.
Often, the advice is to use ice right away after an injury and then heat in the days afterward.
Researchers reporting in the journal Academic Emergency Medicine studied 60 emergency room patients with neck or back pain.
The patients were randomly assigned to either heat treatment or a cold pack for 30 minutes.
No one reported any big improvement in their pain.