"And here were the questions: What did he eat? Did he believe in isometrics? Isotonics? Ice and heat? How about aerobics, est, ESP, STP? What did he have to say about yoga, yogurt, Yogi Berra? What was his pulse rate, his blood pressure, his time for the 1OO-yard dash? When he finally heard the one about how "I couldn't drive as far as you run"!
What was the secret, they wanted to know; in a thousand different ways they wanted to know The Secret. And not one of them was prepared, truly prepared to believe that it had not so much to do with chemicals and zippy mental tricks as with that most un-profound and sometimes heart-rending process of removing, molecule by molecule, the very tough rubber that comprised the bottoms of his training shoes. The Trial of Miles; Miles of Trials. How could they be expected to understand that"
What Cassidy was explaining is quite simple, he was fast because he ran a lot of miles. There are many aspects of running, many types of workouts that one can follow. But the single most effective path to running faster is by running more miles, even if many of them are easy miles.
There is a physiological basis for this. The more you run the more you stress the body, the more the body adapts, and more efficient it becomes at running. The heart gets stronger and requires less effort to pump blood,and the lungs get more adept at providing oxygen to the blood. Your muscles adapt by creating more capillaries, allowing more oxygen to get to the muscles faster. The cells of your muscles develop more mitochondria, enabling the muscle to utilize more oxygen. The body's ability to utilize oxygen is the single most important factor in determining running performance! This is true regardless of whether your are training for a 5k or a marathon.
Results from over distance training does not appear over night. The training you do this week will most likely benefit you 2 weeks from now. It will take several weeks of increased mileage for your body to truly adapt to the training. Once your body adapts it hangs on to the benefits for a longer period of time than any other type training.
How much is enough? Obviously running 20 miles a week will produce better results than 10 miles a week. So any increase in your weekly mileage will begin to provide results. 60 miles a week is where your body gains the most benefit from training.
A word of caution here, increasing your mileage to quickly can also lead to injuries, so it is best to develop a schedule that allows you to increase your weekly mileage incrementally 10%-15% a week over several weeks. Also keep most of your running at an easier pace on the weeks that you increase your mileage. Once your body has gotten used to running higher mileage weeks you can mix in harder running. Over time your speed will show up, though it may not seem like it when your legs are tired from this "Base" training. Don't try to get into shape in 2 weeks, it won't happen! Think long term.