Sorry about that. Unfortunately running is a fairly high risk activity if you try to be competitive and train for faster times. If you take it completely casually and just do 3-4 easy runs a week at a slow pace then its safe as houses, if you want to get your race times down then you have to push yourself to force adaptions and then the risk of injury increases rapidly sadly. The stats for runners are really not that encouraging, between 37-56% chance of an injury every year!
http://www.ncbi.nlm.nih.gov/pubmed/1439399
If you have sufficient mental strength then it is easy to push yourself too hard, beyond your bodies limits, just as I found out recently. If you are determined then it is relatively easy to push beyond safe limits for your current muscular-skeletal condition t handle - running intervals too hard, too many long runs, running all your runs too fast, not enough recovery time etc. It gets hard to simply run at 9:30 a mile for 5 miles when you find it easy to run 7:30 a mile for 12 miles but the latter increase injury risk exponentially.
There are a couple of issues. Primarily, your ability your increase cardiovascular fitness is orders of magnitude faster than increasing muscular-skeletal condition. In a few months you can raise your CV fitness a lot, especially with interval training and the like. But getting your bones, ligaments, tendons, organs, muscles to cope with the increase speed, increased force and increased repetitive pounding can take years. The faster your run the higher the impact force and the greater the injury risk. The other factor is that there isn't really a skill or technique to running, its just fitness based, so you can very quickly ramp up your running speed and running distance simultaneously withut your body having time to strengthen. Compared to say swimming where there is a load of technique involved.
As I realize now there is no fast track to being a fast runner. You can easily train harder, that is ironically is the easy part, but training harder will tend to push your body beyond its limits. You have to train slower and have longer term goals. The fact that marathon training schedules are all 12-18 weeks probably doesn't help. Its probably better to imagine 6-9 months of training, with the first 3-6 months simply a very slow and steady build up before you have a final 2-3 months of specific training with a little more intensity.
