Trigger points, also known as trigger sites or muscle knots, are described as hyper-irritable spots in skeletal muscle that are associated with palpable nodules in taut bands of muscle fibres. The palpable nodules are small contractions or knots in a muscle and a common cause of pain. Compression of a trigger point may elicit local tenderness, referred pain, or a local twitch response.
The local twitch response is not the same as a muscle spasm. This is because a muscle spasm refers to the entire muscle contracting, whereas the local twitch only involves a small twitch and no contraction of the actual muscle.
Activation of trigger points may be caused by a number of factors, including acute or chronic muscle overload, disease, psychological distress (via systemic inflammation), homeostatic imbalances, direct trauma to the region, accident trauma (such as a car accident), which stresses many muscles and causes instant trigger points.
Trigger points form only in muscles. They form as a local contraction in a small number of muscle fibres in a larger muscle or muscle bundle. These in turn can pull on tendons and ligaments associated with the muscle and can cause pain deep within a joint where there are no muscles. When muscle fibres contract, they use biochemical energy, and depletion of these biochemicals leads to accumulation of fatigue toxins such as lactic acid. The tightened muscle fibres constrict capillaries and prevent them from carrying off the fatigue toxins to the body’s recycling system (liver and kidneys). The build-up 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. Many trigger points have pain patterns that overlap, and some create reciprocal cyclic relationships that need to be treated extensively in order to remove them.
The therapists may use myotherapy (deep pressure), dry-needling, “spray-and-stretch” using a cooling (vapocoolant) spray, and stretching techniques that invoke reciprocal inhibition within the musculoskeletal system. Practitioners use elbows, feet or various tools to put/place pressure directly upon the trigger point.
Successful treatment relies on identifying trigger points, resolving them and elongating the structures affected along their natural range of motion and length. Fascia surrounding muscles should also be treated, possibly with myofascial release, to elongate muscles and resolve strain patterns, otherwise muscles will simply be returned to positions where trigger points are likely to re-develop.
The results of manual therapy are related to the skill level of the therapist. If trigger points are pressed for too short a time, they may activate or remain active; if pressed too long or hard, they may be irritated or the muscle may be bruised, resulting in pain in the area treated. This bruising may last for 1–3 days after treatment, and may feel like, but is not similar to, delayed onset muscle soreness (DOMS), the pain felt days after overexerting muscles. Pain is also common after a massage if the practitioner uses pressure on unnoticed latent or active trigger points, or is not skilled in myofascial trigger point therapy.