I found an article that was posted to our marathon training page & thought this excerpt might be helpful to you:
It’s from “Why Running Form Matters: And how you can improve your form” by Scott Douglas
“Are You Overstriding?
There’s a difference between overstriding and having a long stride. Overstriding means that your feet land significantly in front of your center of gravity. When this happens, you’re unable to make full use of your fitness, because you’re braking with every step. And you might soon be breaking with every step, in that overstriding amplifies the already-strong impact forces of running and therefore can contribute to more strain on your bones, muscles and ligaments.
Coach Roy Benson suggests these two methods of determining if you’re overstriding.
1. Have a friend with a video camera stand 20 yards back from the side of a level surface. Run past your friend for 30-40 yards at an easy pace. Then run past at around 10K race pace. Finally, run past at a near sprint. Says Benson, “When you watch yourself, even though you might not be able to stop action and analyze it at that level, just by seeing your form you can recognize whether you’re overstriding. As long as your knee is bent and your foot is coming down back underneath you or close to you there’s probably not much inefficiency and not much risk.”
2. Have a friend stand in front of you while you run toward her at the three effort levels in the above exercise. Says Benson, “The friend looks to see how much of the sole of your shoe is showing on impact. If there’s 4, 5, 6 inches of daylight between your toe and the ground when your heel hits, you’re overstriding.”
The three effort levels are important, Benson explains, because many runners, especially those without a background in scholastic running, become overstriders only when they try to go faster.
To improve a tendency to overstride, practice running fast while landing over your center of gravity. This is often best done by going to a field or other safe, soft surface and shedding your shoes. Says Benson, “At first, jog in place. You’ll be landing on the ball of your foot. That’s what it feels like to be a midfoot striker. Now stay up there and jog in place and lean over and slowly accelerate over the next 50 yards or so and don’t go so fast that you forget to stay up there and land on the ball of your foot. When you do them right, strides like these are fast enough to be a good way to teach midfoot strike.” Then stay conscious of what that footstrike feels like when you do track workouts and other faster sessions.”