How does running slow make you run faster?

There has been a recent shift in thinking about the types of training that makes a distance runner faster while mitigating the risk of injuries.  It has been found that running up to 80% of your  weekly miles at a very comfortable slow pace was optimal for the fastest improvement.  A slow pace can be measured by running at or below 70% of your maximum heart rate (MHR=220 beats per minute minus your age).  For those who don't have a heart rate monitor, another way to measure that you are in this zone is by being able to have a conversation without being out of breath. This “run slow to get faster" methodology has been embraced by the elite running community and some believe has contributed to the multiple recent world records for both men and women in the middle and long distances.  This has also been shown to have the same effect on beginner runners and had tremendous benefits that resulted in improved overall speed performance, while reducing the risk of injury in getting to your race day.