A muscle spasm consists of a strong and painful contraction which is commonly centralised around a strain or tear in the muscle. Electrolyte and neuromuscular imbalances, muscle fatigue and drugs such as diuretics, corticosteroids and estrogens are all causes of excessive spasm with muscle tears and strains. As the injured tissue in or around the muscle activates the pressure sensitive A-delta sensory nerves, there then becomes an intense nociperception/sensitivity and an increased amount of spasm in the muscle.
Muscle spasm associated with a strain or tear causes both the muscle and connective tissue in the muscle to shorten. Because both tissues in the muscle are shortened there is a greater resistance to lengthening/stretching than a hypertonic muscle. Therefore a muscle spasm will show little to no improvement to stretching, palpation or muscle tranquillisers such as acetylcholine due to the connective tissue shortening.
Acupuncture treatment can be of benefit to treating spasms but is unlikely to give complete resolution to the spasm in one treatment. The strains and tears need time to heal before any release of spasm can occur, where acupuncture can come in as a treatment is in shortening this healing process.