How long should a long run be? Time is a better gauge than distance.
That is, the goal of a long run is not to cover a certain distance, but to spend time on your feet.
Run for at least 1 1/2 to two hours. That's the minimum long run roughly 10 to 16 miles to maintain a high endurance level.
Increase your long runs by no more than 15 minutes at a time. Any more and you're setting yourself up for injury or illness. For marathoners, 26 is better than 20. Exercise physiologist David Martin, Ph.D., says one 26-miler is better than several 20-milers: "Milers run miles in practice, 10K runners run 10Ks, so why shouldn't marathoners cover their distance in practice, too?"
Adds 1972 10,000-meter Olympian Jeff Galloway: "Long runs of 26 miles train the body to do what is required of it during the event." However, both Galloway and Martin advise building up to 26 miles gradually over a period of months.
How fast? There are reasons for easing back on the throttle during your 20-milers, and they agree with common sense:
Long runs at race pace may be workouts in your mind, but they're races for your body. That's a lethal mix that can easily lead to overtraining, injury or illness. "Running long runs too fast causes more problems than any other training mistake," Galloway says.
Fast long runs miss the point. "Long runs are endurance workouts, not speed workouts," says Steve Jones, former world record holder in the marathon. "You get speed from other workouts during the week."
Adds Galloway: "Training is like putting together a top-of-the-line stereo system. Long runs are the endurance component. Speed is a separate component entirely."
The ideal pace for long runs is at least one minute per mile slower than your marathon pace. Preferably, it's 1:30 to 2:30 slower a pace at which you can carry on a conversation (not one in monosyllables, either).
Remember: The goal of the long run is time spent on your feet.