As is the case for the majority of people, running pain/injuries generally only bother them when they run (and sometimes for a bit after). When runners stop, the pain stops. However, as soon as they return, the pain also returns. This happens because running is a complex series of events that occur through the body (called the kinetic chain). Akin to a link of chains, if there is weakness (or stiffness) in one or more links in a chain, the energy transfer in that link of chains is disrupted (usually the chain breaks). As your foot hits the ground, muscles up the leg need to contract in a certain sequence to propel your body forward. As this is happening on one side of your body, the other side of your body using muscles in a different sequence to swinging your opposite leg forward to prepare for the next stride. There are many things that can go wrong during these sequences:
-Poor movement at the ankle (over-pronation, or lack of pronation)
-One foot hitting the ground harder than the other
-One foot being on the ground longer than the other
-Lack of stability of the knee causing knee to fall inwards
-Lack of stability of the hip causing hip to wobble (like a model walking down a runway)
-Poor movement in the Sacroiliac joint (the join between the spine and the hips)
So running is not a simple as putting on your shoes and going for a run. It is quite complex. To be able to perform at running, you need to be able to repeat the same sequence of events repeatedly, without failure. If you are unable to do this, it will lead to pain and injury!