If you have ever watched the opening intro to "Baywatch" you can easily envision too much vertical movement in your stride. The characters look like they are running on the moon with big, bounding, leaping strides. Although it may look like a powerful stride, all that bounding requires, and wastes, a lot of energy. To run most efficiently you want to produce just enough lift to overcome the force of gravity and move yourself forward; any more than that is wasted energy that adds up big time.
Lets assume you run produce just 1cm more vertical motion than you need to overcome gravity. Running an 8 min. mile pace at 80 strides per minute will then create 640cm, or 64 meters of excess vertical movement per mile. Over the course of a 5k you will have projected yourself well over a tenth of a mile upwards that you did not need to. That is a problem!
An efficient runner looks like they are gliding over the ground. You see little head bob and their leg motion has a smooth high turn over- almost akin to cycling. Overcoming excessive vertical oscillation not only improves efficiency it greatly decreases impact forces helping prevent injury. In fact over striding and excessive impact forces are the two key factors in running related overuse injuries.
Where to begin? I like to start with fast walking. The difference between walking and running is that when you walk you always have one foot on the ground whereas with running both feet are off the ground. In other words you are always anchored to the ground when you walk preventing you from bouncing. It is important to note that elite race walkers walk at a pace that most runners can not come close to- well under 7 min. mile pace. They accomplish this by fast turn over and extreme efficiency; which is exactly what most runners lack. Many runners would be be better served with a fast walk over a slow, bouncy, inefficient run!
Start off by progressively fast walking to your walk/run threshold which for most will be around 15 min. mile pace. Perform this several times focusing on increasing your turn over and leg speed. The drill is to smoothly transition from a very fast walk into a run without dramatically increasing vertical oscillation. This walk/run progression drill more than any other in my opinion begins to get the athlete to sensate smoothy skimming over the ground. With each repetition run speed should be increased but fast turn over maintained. For most it is a completely different way of running and they can feel the dramatic reduction in impact forces. As speed increases the stride opens up but again fast stride rate and low oscillation is maintained. Before and after video will often show a "night and day" difference in form at the same pace.
It is important to note that very fast walking can be an integral part in run training, especially for beginners. Fast hill walking for example is great to develop strength endurance needed for running without the impact. Incorporating the walk/run progressive drill regularly into your training regime is a great way to start improving your running efficiency. I recommend performing these drills before each training session and then attempt to carry the improved form into your training run.