Running is hard. If you're targeting a goal—whether it's entering your first race or qualifying for Boston—you spend a lot of time pushing your limits. So when it comes time to run easy, you happily succumb to your inner plodder, right? Nope. "Not running slow enough on easy days is probably the number-one error runners make," says Greg McMillan, M.S., an exercise physiologist and running coach in Flagstaff, Arizona.

More: How to Avoid Common Running Mistakes

Consciously or not, many runners push too hard on easy runs and miss out on their varied benefits—like time to heal, for one. Demanding workouts like speedwork and long runs put a great deal of stress on muscles, and "any time there's a stress, you have to allow some recovery time for those tissues to rebuild," McMillan says. Time spent going easy also builds your fitness base and staves off burnout. "Easy runs allow you to focus on enjoying the run and your surroundings," says Michael Sachs, Ph.D., a sports psychologist at Temple University.

More: 5 Phases to Speed Up Your Running Recovery

Rule #1: Run Slow Often

It's easy: Seventy percent of your weekly mileage should be easy miles. Depending on your age and fitness level, your muscles need 30 to 60 hours to recover from a hard effort, says McMillan. (Long, slow runs lasting 1.5 to 2.5 times longer than your average weekday run count as hard efforts due to their duration.) Running super slow and relaxed for one to three days after tough workouts gets blood flowing to muscles, which flushes away broken-down proteins, delivers new proteins to rebuild damaged tissue, and carries carbohydrates to replenish depleted stores in muscle cells. "That gentle exercise bathes muscles in the good stuff they need and removes all the bad stuff caused by the prior training," McMillan says. "And running as part of your recovery makes your body say, 'Oh, I'm still getting this stress—I better build this tissue even stronger.'"

More: 4 Tips to Run the Stress Off

Rule #2: Heed Your Watch—or Listen to Your Body

"Could I go farther or faster with no problem?" Running based on feel rather than time allows for variations in weather, wind, and terrain. "The body doesn't know pace, it only knows intensity and duration," McMillan says. "Tuning in to that is really important."

More: 6 Tips to Tackle Any Terrain