A large number of factors have been identified as causes of trigger point activation. These include acute or chronic overload of muscle tissue, disease, psychological distress, systemic inflammation, homeostatic imbalances, direct trauma, radiculopathy, infections, and lifestyle choices such as smoking. Trigger points form as a local contraction of muscle fibres in a muscle or bundle of muscle fibres. These can pull on ligaments and tendons associated with the muscle which can cause pain to be felt deep inside a joint. It is theorized that trigger points form from excessive release of acetylcholine causing sustained depolarization of muscle fibres. Trigger points present an abnormal biochemical composition with elevated levels of acetylcholine, noradrenaline and serotonin and a lower ph. The contracted fibres in a trigger point constricts blood supply to the area creating an energy crisis in the tissue that results in the production of sensitizing substances that interact with pain receptors producing pain. When trigger points are present in a muscle there is often pain and weakness in the associated structures. These pain patterns follow specific nerve pathways that have been well mapped to allow for accurate diagnosis or the causative pain factor.