Take It Easy (and Hard)

Old CW: Make every run count.
New CW: Use the "hard-easy" rule.

Use a 1-to-10 scale to rate how challenging your workouts are. Most runners hover around a 5 (not hard, not easy) day after day after day. Today's top runners avoid this gray zone by doing runs that are either truly challenging (8 and above) or very easy (3 and below).

The reason? The biggest fitness gains come from the hardest workouts—but you can't take yourself to the limit every time you lace up your Asics. Follow the hard-easy rule and you can achieve better results with the same total amount of training you're doing now. You'll be able to push harder on some days by allowing your body to recover on others. This will help you avoid overtraining, and you won't tire from a repetitive routine.

Let's say you run four times a week at level 5. This week, try doing two level-8 runs (one long run and one speed session) and two level 2's (short, easy runs). Either approach adds up to 20 effort "points." Stick with the hard-easy schedule for a couple of months and check your race times. Your numbers should be smaller.

http://www.menshealth.com/mhlists/running_efficiently/Take_It_Easy_and_Hard.php