LEAVE IT UP TO A PIECE OF PAPER TO TEACH YOU TO RUN EASY

BEFORE I FELL for running, I thought the hardest thing about the sport was the fast stuff: the speedwork, the sprints, and the intervals.

And I do find that running fastmaking my lungs beg for air, feeling my heart pounding all the way in my ears, and pushing my legs to their limits is indeed hard. Some days nearly impossible.

But no: Turns out, the hardest thing about running is keeping the easy miles easy.

The irony is not lost on me that, somehow, breathing evenly enough to be able to talk while running, keeping my heartbeat under control, and moving my legs only to the point where they feel comfortable with the effort can be considered a challenge at all. But ever since I started running consistently three years ago (which coincides with my start date at Runner's World and definitely not by coincidence), keeping it slow-all the while knowing I could be running so much faster-makes me feel like I'm not trying hard enough.

Why am I even talking about this, you ask? Some 80 percent of your weekly mileage should be at an easy pace (including your long run), no matter the type of training, because adaptations in the body happen during easy efforts. These miles are aerobic, meaning they help increase capillary densities, which are tiny blood vessels that deliver oxygen and nutrients to muscle cells and, in turn, improve aerobic capacity, the amount of oxygen your body can use while running. Moreover, it teaches your body to use fat for fuel and conserve glycogen (the stored form of glucose that comes from carbohydrates).