Lactic acid is created by muscle movement, and muscle knots form when the hydrogen ions in lactic acid fill muscles, explains TriggerPoint Yoga. This is particularly likely to occur with the repetitive movement of strength training.
Muscles need lactic acid to move, according to TriggerPoint Yoga. Lactic acid can be moved from the muscles by the body, but sometimes it is generated faster than it can be moved. The body does not cleanse the muscles of all the hydrogen ions created during physical activity or repetitive movement. If the surplus is not flushed away, the muscle fibers contract and form a knot.