Running might seem like a straightforward activity to take up to improve your fitness. However, it's not quite as straightforward as it may seem with some scientific studies finding that up to 70% of runners get an overuse injury each year. Depending on how bad that overuse injury is and just how it is maintained, many runners just give up and do not continue to run. The the things that cause running overuse injury are multiple but are associated with problems such as doing too much running too early before letting the body to adapt to the increased levels of exercise. Poor running shoes with design features which do not go with those of the runners needs may also be an issue. Issues with foot biomechanics and the running technique may also be problems at increasing the chance for an injury.
A good example of an overuse injury is anterior compartment syndrome. There is fibrous fascia around muscles which support the muscles in place. In the event that fascia is tight, if we exercise the muscle will need to expand but that tight fascia inhibits it. That compression inside the fascia compartment may be painful. In anterior compartment syndrome, this affects the muscles that are on front of the lower leg. The most frequent cause of this condition is what is known as overstriding. In this the runner is hitting the ground with their leading leg too far in front of the body. To lower the foot to the ground, the anterior leg muscles need to work harder. As they work harder, the muscles expand and if the fascia doesn't allow it, then this will end up painful. It is going to only hurt when running and will not be painful when not running. The best way to deal with anterior compartment syndrome to use approaches for the runner to shorten their stride length to ensure the front foot does not make contact with the ground too far in front of the body when running.