Over-used muscles (and other soft tissues) change in three important ways:

• acute conditions (pulls, tears, collisions, etc),
• accumulation of small tears (micro-trauma)
• not getting enough oxygen (hypoxia).

Each of these factors can cause your body to produce tough, dense scar tissue in the affected area. This scar tissue binds up and ties down tissues that need to move freely. As scar tissue builds up, muscles become shorter and weaker, tension on tendons causes tendonitis, and nerves can become trapped. This can cause reduced range of motion, loss of strength, and pain. If a nerve is trapped you may also feel tingling, numbness, and weakness.