Muscle scar tissue usually forms after an injury. The scar tissue that forms doesn't function as optimally as the old tissue did, and therefore can cause pain. While muscle scar tissue can be painful, it may not always be apparent while you are exercising, unless the scar tissue is being stretched.
Regular muscle fibers run parallel to each other in a neat, orderly route. When scar tissue forms, it is a knotty, tangled and twisted mess, which is where pain may occur. Scar tissue is inelastic and won't move as easily as your muscle did pre-injury. Because of its effect on movement, scar tissue located by a joint can also cause joint problems from improper form and movement, which may lead to future complications.
Painful Scar Tissue
When connective tissue is injured, the nerve tissue in that surrounding area is injured as well. When nerve tissue is damaged, it reacts by growing smaller, immature nerve branches, which the Doctor Schierling website explains are up to 1,000 times more pain sensitive than normal tissue. The scar tissue forms as a protective measure that will avoid overstretching the muscle, which is sometimes how the injury may have originally occurred. Therefore, stretching of scar tissue can also be very painful.
Exercising too soon after scar tissue has formed is likely the most painful time to exercise because the new nerve tissue is still developing. Any exercise that stretches the scar tissue will also cause pain. For example, if you tore your quadriceps muscle just above the kneecap, any bending at the knee, such as with squatting or lunging, will stretch the muscle and cause pain. An old rotator cuff injury that formed scar tissue around your shoulder joint may cause pain when you move your shoulder in all directions.
Scar tissue won't always be painful during exercise, but it will leave the area more susceptible to re-injury. Chronic pain around the scar tissue should be treated by a doctor, because that can lead to degeneration and osteoarthritis, among other joint and muscle problems. Depending on the location of the tissue, surgery may be required. Using a foam roller for self-myofascial release can reduce adhesions and scar tissue formation, leading to less pain after time.