Trigger points are described as hyperirritable spots in muscle that are associated with palpable nodules or taut bands of muscle fibers. The trigger point model states that pain frequently radiates from these points of local tenderness to broader areas, sometimes distant from the trigger point itself. Referred pain patterns have been identified from trigger points.

iStock 000006209199XSmallActivation of trigger points may be caused by a number of factors, including acute or chronic muscle overload, activation by other trigger points (satellite trigger points), disease, psychological distress, direct trauma to the region, accident trauma (such as a car accident which stresses many muscles and causes instant trigger points), radiculopathy, infections and health issues such as smoking.

Trigger points form only in muscles. They pull on tendons and ligaments associated with the muscle and can cause pain deep within a joint where there are no muscles. When muscle fibers contract, they use biochemical energy, and depletion of these biochemicals leads to accumulation of fatigue toxins such as lactic acid. The tightened muscle fibers constrict capillaries and prevent them from carrying off the fatigue toxins to the body's recycling system (liver and kidneys). The buildup of these toxins in a muscle bundle or muscle feels like a tight muscle.

When trigger points are present in muscles there is often pain and weakness in the associated structures. These pain patterns in muscles follow specific nerve pathways and have been readily mapped to allow for identification of the causative pain factor. Compression of a trigger point may elicit local tenderness, referred pain, or a local twitch response. Many trigger points have pain patterns that overlap, and some create reciprocal cyclic relationships that need to be treated extensively to remove them.

Myofascial dry needling is one form of therapy that treats trigger points successfully. For those people who may be weary of needles, trigger point therapy by pressure (also known as ischaemic compression) has also been found to be very effective.