Have you been working out a lot lately, or started a new hobby and you're a little sore? What should you be using to help alleviate the pain?
If you have injured your self or have an over use injury. It is good to use Ice right away. Ice will not heal your injury, but ice is very effective for reducing swelling and inflammation. If swelling does not subside, you should seek medical help.
Lets say you tweaked your back or have some sore aching muscle, then heat is the way to go. But only if there is no swelling or inflammation, then you should continue with ice. Heat should be used on the lowest setting first and is good for helping relax and sooth your tight muscles. You should not use heat for longer than 30 minutes and do not use ice to cool the area down.
Alternative heat and ice is not effective and should not be done unless prescribed by your doctor. Ice or cold with constrict the blood vessel and then adding will heat will open up the blood vessels and this will results in a open and tightening of the blood vessels and we do not want that if we are trying to sooth an injured area. Depending on your injury timeline or cycle, you will always want to use one or the other, not both at the same time.
Of course any new or lingering injuries should be looked at by a doctor as there may be something more serious going on.