Trigger points are hyper-irritable spots that are in the skeletal muscle, they commonly occur with nodules found in taut bands of muscle fibres. Compression of trigger points may cause a twitch response, local tenderness or referred pain. Palpation of trigger points may bring on the pain, whilst adding pressure to the point may release the pain.
An active trigger point is one that actively refers pain either locally or to another point:
A latent trigger point is one that exists but does not yet refer pain yet but may do when pressure is applied.
A key trigger point is on that may cause a latent trigger point due to the nerve pathway.
A satellite trigger point is one which is activated by a key trigger point. Successfully treating the key trigger point often will resolve the satellite and return it from being active to latent, or completely treating it too.