The dry needling is aimed at treatment of trigger points. Trigger points, defined very simply, are the points where muscle tissue is more shortened, so that you are missing nutrients and, therefore, is hypersensitive to touch. You can also take a radiating pain.
The idea is to treat this area of maximum contracture (myofascial trigger point) by the introduction of a needle, usually in acupuncture at the trigger point. This makes the central nervous system begins a process of regeneration of the damaged muscle so that more nutrients reach, and if the puncture is successful, the muscle relaxes and disappear entirely symptoms such as local pain and radiating pain.