Muscle spasm pain can be quite severe. Pressure and Pain receptors in the muscle fibers become activated and a local inflammatory response is mounted. The increase in local inflammation serves to increase the pain and further irritate the muscle in spasm. This does not have to affect the whole muscle and can involve only some fibers, causing myofascial trigger points. These are places in a muscle that go into spasm and inflame the covering of the muscle locally. These can be exquisitely painful and send referred pain to other parts of the body.