Stretching for Runners
The current research pre run has massively come away from the Static stretch and moved towards a more dynamic warm-up to improve functional mobility for your run and we would agree with this approach for the majority of runners.
The time to statically stretch, we feel, is after your run when the muscles are warm and extensible. The stretch should be felt but never sharply painful.
The other point to remember is that if you spend time improving your muscle flexibility you then need to strengthen it so that you have strength through your full range of movement, but we will cover the strengthening exercises for runners in another post.