Smart Zones are designed to easily and accurately delimit the low (Endurance), moderate (Race) and high (Peak) intensity zones specific to your body, based on your heart rate and breathing.
Throughout the week, aim to run in the Endurance Zone 80% of the time by doing slow, comfortable runs and then go hard! Those easy runs will build up an itch for that sprint like an elastic being pulled back. Practicing such restraint can be surprisingly difficult at first, but if you take a leap of faith and follow through with your plan to slow down, your intensity discipline will be well-rewarded.
Don't let old habits get in the way of running slower. Think of the long-term effects and benefits, and how you're taking care of your body by running following the 80/20 philosophy.