Driving your heel into the ground with every step creates a braking force that slows your forward momentum. Every step is reduced to a braking action with slows forward movement followed immediately by a pushing off force to re-accelerate to maintain pace. Here’s an experiment for heel strikers:
Situation 1: Get in your car. Go to a road with no traffic. Accelerate for one mile without touching the brake. Notice it’s smooth and seamless. This is equivalent to running with good form.
Situation 2: Now do the same thing, except this time tap your brakes about 140 times each minute as you drive the same mile. This is what you are doing when you overstride with a heel strike.
How did that work out for you? Notice a significant difference?
This is a great metaphor to explain the difference between heel and mid or front foot striking.
For years, I was a heel sticker and I still need to constantly be mindful of my form as I run. Sometimes I catch myself letting go and loosing form.
Someone in the comments of that post wrote:
Fred Flinstone used his heels to stop his car… Not speed up.