Runners in final preparations for the Austin Marathon on Feb. 14 are thinking now about pace.

Even casual observers have heard of "the wall" at the 20-mile mark. How do you pace yourself to make it past "the wall" and on to the finish line at 26.2 miles?

The obvious strategy is to slow down. Set a slower pace to conserve energy. In fact, run with someone who is slower.

Good idea? Maybe not.

"I've talked to many runners who run a marathon with a slower runner just to help them out, and they find it's not easy at all," says Jay Hilscher, a local running coach, who has run a national class 2:27 marathon.

The key is that running more slowly is not necessarily a more metabolically efficient way to get to the finish line. In fact, research indicates that in terms of energy cost (calories burned), each runner has an optimal pace, and it may be faster than they thought.

"When I ran 2:27:57, it felt a lot easier than when I later ran a 2:32," Hilscher says. "I ran maybe 10 minutes slower in the second half when I ran the 2:32."

Experienced runners may be familiar with their optimal marathon pace, and what it feels like. They've run the pace in training enough so that they're able to mentally lock into it.

For many runners, the optimal pace will be about a minute per mile over the pace they ran in their most recent 10K. Those who ran the recent half-marathon might find that their optimal marathon pace is about 35-40 seconds per mile slower than the half-marathon pace.

About a year ago, researchers published a study in the Journal of Human Evolution suggesting that the optimal running speed — the pace burning the fewest calories — was considerably faster than once thought. University professors Cara Wall-Scheffler and Karen Steudel collected data on nine people running on a treadmill at different speeds, ranging from a 13:20 minute per mile pace to a 5:30 pace. Each person ran six different speeds: two slow, two comfortable and two fast. The researchers then measured how many calories the runners burned at each speed.

According to their research, the age-old tenet that you burn the same number of calories (about 100) whether you jog a mile, or run a fast mile, does not hold up. What they found was that everyone has a unique optimum running speed that burns the least amount of calories and is therefore the most efficient.

The average optimal speed for women in the study was a 9:15 per mile pace; for men it was a 7:15 per mile pace. And runners who ran slower or faster than their optimal pace burned more calories. The researchers found that the slowest running speeds were the least metabolically efficient.

Haile Gebrselassie set the world marathon record of 2:03:59 in 2008. That's 4:44 minutes per mile. Steudel and Wall-Scheffler believe he achieved that by running at maximum efficiency.

"I don't think he'd be able to maintain that sort of pace over that distance unless he were running at max efficiency," said Wall-Scheffler. "In a competitive setting, the trained mind and body will arrive at the optimal pace. People who run a lot know the pace that will work best."

"On the other hand, less experienced runners may be caught thinking 'this pace feels the best' (because it's easy), and it may not actually be the best or optimal pace."

"Research often backs up what we intuitively already know," says Hilscher. "I would agree that there's an optimal pace that's most efficient. Obviously if you go too fast, you blow up. I tell marathon runners that first, not to be nervous, and enjoy themselves. As far as pace goes, I say, 'Relax the first 10-13 miles, and after that assess your pace but don't obsess about it.' I think runners will recognize their optimal pace."