One of the things runners do not like is an injury that prevents them from running. Some minor injuries only require a few days to recover while others may last several months. Usually, a major type of injury such as a torn ligament or cartilage in the knee can lay a runner up for several months. An additional problem occurs when after the injury has healed there are still some issues. The period of inactivity has caused some of the muscles used in running to be weakened by the lack of exercise. With weakened muscle strength, the return to the normal running style is off. It might be a problem with stride length, push-off strength, a favoritism toward the once-injured knee that limits a normal gait or even an irregular foot plant on the injured leg. And with this altered gait, the runner’s muscles and posture may be changed slightly, which again causes more problems and even another injury.
Even an injury to another body part may lead to problems in running. Newton’s Law of “For Every Action, There is an Equal Reaction” applies in this case. An injured shoulder may prevent the arm from moving in the normal motion. Holding the arm tight against the side to prevent movement has a reaction to the legs' normal gait. The altered gait in the legs leads to a change in muscle action and balance of the runner’s weight to offset the lack of movement from the injured shoulder.
A pulled muscle in the low back will change the posture a runner normally has. I remember coming up on a friend in a race and seeing him bent over to his side and leaning forward at the waist. I asked him, “Is this your new running form?” He had an injury that prevented him from standing up straight and he was trying to find a position with his upper body to lessen the pain. He would have been much better lying down and resting. But, being an addicted runner, he was out trying to run a 10K race. He just laughed and told me later the comment regarding his running form was the only thing that helped him finish the race.
