The Long Run - A Great Summary

From RunCoachJason.com

The purpose of easy and long runs is to stimulate the physiological, biochemical, and molecular adaptations needed for endurance, including the storage of more fuel (glycogen) in your muscles, an increased use of intramuscular fat at the same speed to spare glycogen, an increased number of red blood cells and hemoglobin, a greater capillary network for a more rapid diffusion of oxygen into the muscles, and an increased mitochondrial density and number of aerobic enzymes to enhance your aerobic metabolic capacity. Since many of these adaptations are volume-dependent, not intensity-dependent, the speed of easy runs is not as important as their duration. The single biggest mistake competitive runners make is running too fast on their easy days. By doing so, they add unnecessary stress to their legs without any extra benefit and they won’t be able to run as much quality on their harder days.