Cramps, shin splints, and chest pain: what to do when running hurts
There is actually quite a bit written about side cramps or stitches (these terms are used interchangeably). It is a cramping of the abdominal muscles – diaphragm. Most often it is on the right side but most definitely it can be on the left or both sides. You may even get a deferred pain in your shoulder due to nerve connections.
First, the huge consensus is that a more novice runner or an out of shape returning runner are by far the most likely to experience a stitch.
Second, stitches can often be traced to faulty breathing.
Third, and related to the first two, is running downhill (and occasionally uphill). Because we alter our body alignment or posture, we stress those abdominal and respiratory muscles differently. We are not in shape for this type of running.
Mostly, it is related most often to a newer runner or someone out of shape, or someone pushing themselves to higher levels (or on new terrain) than they have prepared for in training. In each case, your breathing becomes increasingly relied on to supply your body with oxygen due to the work load. The work load is relative so it makes sense in each case that these people are most susceptible to side cramping.
Prevention & Cures for Stitches
At the foundation of ridding yourself of stitches is progressively getting in better shape. As your diaphragm and intercostal muscles get more exercise they begin to accommodate to heavier breathing for longer periods of time. These muscles are in no different situation than your leg muscles for running; they have to be conditioned. Like I always say: "Repetion is the best teacher!"