20. The Hard/Easy Rule
Take at least one easy day after every hard day of training.
"Easy" means a short, slow run, a cross-training day or no exercise at all. "Hard" means a long run, tempo run or speed workout. "Give your body the rest it needs to be effective for the next hard run," says Todd Williams, a two-time U.S. Olympian and online coach at pushthepace.com. Apply the hard/easy rule to your monthly and yearly training cycles by treating yourself to one easy week each month, and one easy month each year.
The Exception: After the most exhausting long runs and speed workouts, especially if you're 40 or older, wait for two or even three days before your next tough one.
More from Runner's World: The World's Simplest Beginner Plan
21. The 10-Degree Rule
Dress for runs as if it's 10 degrees warmer than the thermometer actually reads.
To put it another way, dress for how warm you'll feel at mid-run—not the first mile, when your body is still heating up. This means choosing the right apparel. (See the "Dress for Success" table) "On cold days, the new soft-shell tops and tights are light, warm and breathable," says Emily Walzer, fabrics editor for Sporting Goods Business Magazine. "On warm days, wear a lightweight performance fabric next to your skin, which will disperse sweat through evaporation."
The Exception: There's a limit to how many clothes you can take off without getting arrested, so if it's in the 70s or warmer, wear minimal lightweight, light-colored apparel.
More from ACTIVE: 6 Tips to Run Through the Heat
22. The Speedwork-Pace RuleThe most effective pace for VO2-max interval training is about 20 seconds faster per mile than your 5K race pace.
The best way to increase your aerobic capacity and long-distance speed is through VO2-max interval training. A pioneer of VO2-max training is Jack Daniels, Ph.D., coach at the Center for High Altitude Training in Flagstaff, Arizona. "By stressing your aerobic system," he says, "this pace optimizes the volume of blood that's pumped and the amount of oxygen that your muscle fibers can use."
The Exception: The exact pace is closer to 10 seconds faster per mile than 5K race pace for fast runners, and 30 seconds faster per mile for slower runners.
More from ACTIVE: How to Improve VO2 Max
23. The Tempo-Pace Rule
Lactate threshold or tempo-run pace is about the pace you can maintain when running all-out for one hour.
This pace is about 20 seconds slower per mile than your 10K race pace, or 30 seconds slower per mile than 5K race pace. "The key benefit of this pace is that it's fast enough to improve your threshold for hard endurance running, yet slow enough that you don't overload your muscles," says Daniels. The ideal duration of a tempo run is 20 to 25 minutes.
The Exception: The exact pace is less than 20 seconds slower per mile than 10K race pace for faster runners and slightly more than 30 seconds slower per mile than 10K race pace for slower runners.
More from ACTIVE: What are Threshold and Tempo Runs
24. The Long-Run-Pace Rule
Do your longest training runs at least three minutes per mile slower than your 5K race pace.
"You really can't go too slow on long runs," says RW "Starting Line" columnist Jeff Galloway, "because there are no drawbacks to running them slowly. Running them too fast, however, can compromise your recovery time and raise your injury risk."
The Exception: Galloway says you should run even slower on hot days.
25. The Finishing-Time Rule
The longer the race, the slower your pace.
How much slower? Jack Daniels and J.R. Gilbert spent years compiling a table (see "Predict Your Performance") that shows how much you should expect to slow down from one race distance to the next. "We did some curve-fitting to come up with a formula that generates a pseudo-VO2-max for each race time," says Daniels. They sweated the math; now you just need to sweat the race.
The Exception: Terrain, weather, or how you feel on race day could all throw off the table's accuracy.
More from ACTIVE: 5 Tips for Marathon Pacinghalf marathon race.