Most areas respond best to ice in the first few days to try and decrease the inflammation.
Additionally, and importantly, nerve conduction works best at 98.6 degrees. So cooing an area interferes with pain sensors conducting pain.
Ice really is a cheap way of anesthetizing an area.
But the back is an usually an exception to the general guide that cold is the best initial therapy.
The muscles that are in spasm are usually not the superficial muscles of the back, but the deep ones, buried under several layers of muscle.
It is difficult to get these deep layers cold enough to really affect the pain. They are just too deep.
Also the mechanism of what is going on for most
people with low back pain is different than pain in other areas.
Low back pain usually
involves muscle spasm, while pain in most areas (fingers, elbows, shoulders, knees) does not involve muscle spasm.
Heat causes relaxation of muscle fibers leading to relief of the spasm.
(Conversely, cold causes contraction of muscle fibers, hence no relief of spasm and therefore no pain relief.)
The above is the reasoning behind why most sources recommend heat for low back pain.
The Claim: Heat Wraps Ease Back Pain http://www.nytimes.com/2007/05/01/he...real.html?_r=0
Notice that the above New York Times article that exercise is recommended after several days and worst pain and spasm has gone away.
Suzanna McGee, who posts here as Sixftlion has a a great tennis fitness site, Tennis Fitness Training.
She has an exercise, "cats and dogs", that seems deceptively simple, but is a good early exercise to flex and extend the back muscles:
"Cats & Dogs Exercise Helps Painful Shoulders, Elbows, Wrists, Lower Back and Knees": http://www.examiner.com/article/pain...-cats-can-help
Over the long term, a stronger core, which includes the back, can help prevent recurrences of low back pain.
While we play tennis for fitness, the serve and big forehands leads to muscle imbalances, and that includes putting undo stress on one side of the back more than the other.
So starting a back conditioning program with at least body weight squats and lunges would be recommended.
[Obviously, not all low back pain is due to muscle spasm. If your back pain is continuing to bother you, you should get checked out medically to see if there is some structural problem like a bulging disc.]