Training for a marathon or half marathon can put a lot of strain on your body. But there are things you can do to improve your form and reduce the impacts.
Watch Your Pace
Believe it or not running at too slow of a pace can cause injury. Figure out your steps per minute (spm) by counting one foot's landing for 30 seconds and multiplying by four. If it's less than 160 spm you are at a higher risk for lower leg injuries. You need to increase your speed by between five and ten percent to reduce stress on the hip and knee joints. An easy way to do this is to download a metronome app to your phone, and increase the beat per minute to the desired rate.
Lean Into It
You don't want to be straight up and down when running. Staying too upright will put more demand on your quads, and increased compressive forces to the knee. Instead use a stance that mimics a plank with your upper body - and then lean forward about ten degrees. Of course, don't lean so far forward that you cannot catch yourself if you trip.
When you walk your body is like a pendulum - with a combination of pulling and pushing motions. This is not the case when you run because there are moments when both feet are off the ground. You need to remove, or at least minimize, the pull component. You can do this by imagining your feet are pushing you forward - like they would when you are kicking off on a skateboard or scooter.
By using the proper running form you will be less likely to suffer injuries - and more likely to make it to the finish line.