Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity. It can happen when you hold or pick up something, or when you stretch or exercise with weights.

Muscle knots are hard, sensitive areas of muscles that tighten and contract even when the muscle is at rest. These tense muscle fibers can cause pain in other parts of the body when touched. Muscle ...

Human movement is reciprocal in nature: Opposing muscle groups must coordinate for proper movement. Muscle length and strength between opposing muscle groups need to be in balance for normal movement ...