How can trigger point therapy release muscles?

Relaxes the area: There are many ways of trigger point therapy. One is just applying pressure over those areas with fingers, knuckels, or with devices ( gun like or ballpoint like). Also those areas may be injected wtih small doses of cortisone with local anesthesia ( xylocaine (lidocaine) or marcaine) and with muscle relaxants like diazepam or alike and even with antiinflamatories like toradol. This tx relaxes the area.

Not known exactly: There are theories ranging from changes in electrical potential within the muscle to release of endorphins. The exact mechanism isn't known and may well be a few mechanisms together during trigger point therapy.