Moving may be difficult because of disorders that restrict joint motion or that cause weakness, stiffness, tremor, or difficulty initiating movement (for example, Parkinson disease). Movement may also be limited when motion causes pain. People with pain in the muscles, ligaments, bones, or joints (see Introduction to the Biology of the Musculoskeletal System) tend to consciously and unconsciously limit motion. This limitation of motion often gives the impression of weakness even though the nervous system and muscles are able to generate movement.
A joint may have limited range of motion because of
Previous joint injury causing significant scar tissue
Prolonged joint immobilization (for example, when a person's arm is paralyzed by a stroke or placed in a sling) causing shortening of the tendons
Fluid accumulation in a joint resulting from arthritis or an acute injury (giving a sensation that the joint is locked)
A piece of torn cartilage (resulting from an injury, typically in the knee) that blocks joint movement
Although many people complain of weakness when they feel tired or run down, true weakness means that full effort does not generate normal, strong muscle contractions. Normal voluntary muscle contraction requires the brain to generate a signal that then travels through the spinal cord and nerves to reach a normally functioning muscle. Therefore, true weakness can result from injury or disease affecting the nervous system, muscles, or connections between them (neuromuscular junction).
Doctors can often diagnose weakness based on the person's symptoms and the results of a physical examination. Doctors first try to determine whether the person can contract the muscles with normal strength. If muscle strength is normal, and the person has difficulty moving a joint, the doctor tries to move the joint for the person while the person relaxes (called passive motion). If motion is painful, joint inflammation may be the problem. If passive motion causes little pain but is blocked, joint contracture (for example, due to scar tissue) or stiffness due to spasticity or rigidity caused by a nervous system disorder may be the problem. If passive motion causes little pain and is not blocked, doctors encourage the person to try as hard as possible to move. If movement is still difficult and still does not cause pain, true weakness is possible.
For joints with a limited range of motion, joint flexibility can be maximized by stretching exercises and physical therapy.
If the joint's range of motion is severely restricted by scar tissue, surgery may be necessary.
The best way to relieve weakness is to treat the disorder causing it, but physical therapy often helps a lot even when no ideal drug treatment exists.