Avoid Injury when Running
More and more people including many friends have started running and usually after six to twelve months they end up asking me what to do about this or that stress injury. While by no means an expert, my past in elite sports does provide me with some kind of reference frame. Also, I've myself asked knowledgeable people the same questions so it's easy to paraphrase.
The cause of the stress injury is usually the same: They are between 20 and 30, ambitious, and used to exercise/biking. This means they are generally fit and especially that their cardiovascular capacity is quite good. Add to this a spark of ambition and what happens once they pick up running is that their muscles and tendons aren't ready for the repeated pounding running tends to induce. To make matters worse, the body doesn't fail at once as these are healthy young individuals and thus the stress injury first occurs after some time at which point recovery is already somewhat of a lengthier process.
To sum up, these aren't 50+ year olds first-time exercisers who need a 2-min run, 2-min walk program, but rather energetic and active people already in good shape whose bodies need to get used to the impact from running.
A few tips to follow in order to avoid injury:
SHOES: It should come as no surprise that a good pair of running shoes is essential. It doesn't have to be the most expensive ones, but don't get the cheap supermarket model either. Also, running shoes tend to wear out after about 1,000 km or two years whichever comes first, that is the shock absorbing effect diminishes. A bonus tip: Get two pair of shoes. This has at least three advantages. First, switching between the two stresses your muscles and tendons in slightly different ways. Second, if you start using your second pair half a year or so after the first, you will always have a pair of shoes that are broken in. Third and lastly, if you run on consecutive days allowing the shoe to rest will restore its impact-reducing effect .
ROUTE: Try to choose a route with as little asphalt/concrete as possible. This not always being doable there's a second tip: Alternate the direction of the route you're running. Being habitual creatures we tend unconsciously to choose the same direction of the route time and again, and as there inevitably are inclines and declines and the surface tilts, you stress your muscles and tendons in the very same way. By alternating you'll make sure to stress both sides of the body.
10-PERCENT RULE: A rule of thumb says that you shouldn't increase the total distance covered in a week by more than 10% in the following week . Remember that your body most likely will not tell you to hold back before it's too late so this has to be a conscious decision. You should also take into account that the pounding of your legs is a lot tougher the faster you run (compare walking with sprinting) so it's not purely mathematical. In short, just be aware not to increase the intensity (distance and speed) too quickly.
INJURY: If a stress injury strikes the treatment consists of rest, rehabilitation and, if you want to get fancy, icing. You might need to have a break. Once you start back up, cut down on your intensity both in terms of distance, number of weekly runs and speed. Even non-acute stress injuries benefit from icing, so placing a bag of ice/frozen vegetables on your shin/knee/ankle after your run speeds up recovery . Albeit I find treadmills close to the most boring thing ever, if you have access to one this can help you control these parameters, and the surface is somewhat softer.
There's really nothing of the above that isn't common sense. Rather, it's the fact that ambition and desire for immediate results quickly take over. As such, these tips are also helpful when starting back up after a winter break.
 The way it was explained to me, there are small air bubbles in the sole providing the impact reduction when you run. After a run these have been squeezed out and need to reestablish themselves, and this process usually take somewhere between 24 and 48 hours. It's also these cushioning air molecules that tend to wear after a certain mileage/time. There are a myriad of sources on this, one being: http://www.runningfit.com/index.php?option=com_content&task=view&id=129&Itemid=85.
 Be sure to wrap the ice in a T-shirt or towel rather than applying it directly as this might harm the skin/tissue. Apply for 15-20 minutes. This is called the RICE-principle (http://en.wikipedia.org/wiki/Soft_tissue_injury).
Thanks to Anders la Cour Bentzon and Martin Borch Jensen for reading drafts of this.