A formula for an ideal marathon pace might stave off hitting the wall

Marathoners typically have two goals: finish the race, and finish the race under a set time without hitting the wall. One researcher thinks he's found a new formula that calculates how much carbohydrates a runner needs to eat and at what pace he or she needs to run in order to complete the race without feeling any ill effects or dropping out.

Running the 2005 New York marathon was the catalyst for the study by Benjamin Rapoport, a student in the Harvard-MIT division of health sciences and technology. He hit the wall during the last few miles of the race, and said in a news release, "You feel like you're not going anywhere. It's a big psychological letdown, because you feel powerless. You can't will yourself to run any faster."

In an intense endurance event such as a marathon, the body burns carbohydrates for most of its energy, and those carbs are stored as glycogen in the liver and leg muscles. When the body runs out of carbs to burn and starts burning fat, an athlete can hit the wall, experiencing symptoms such as pain, fatigue and wooziness. Some runners can bounce back after eating or drinking something carb-based, but that plus recovery time can cost precious minutes in a race.

Rapoport's formula focuses on two factors that he says can restrict performance for endurance runners--aerobic capacity and how capable the leg muscles are at storing carbohydrates as glycogen.

Aerobic capacity is typically measured by VO2max, or the maximum amount of oxygen a person uses during intense exercise. While this can be measured accurately in a lab, runners can also estimate their VO2max by measuring their heart rate during exercise.

The equation uses VO2max to determine a range of running paces, including a reasonable pace that can be run for the length of the race without hitting the wall. The full formula, which runners can use, is available in Rapoport's study released Friday in PloS Computational Biology.

But calculations are only one part of competing in an endurance race, as those who have competed in them can tesitfy. Weather conditions, course terrain and mental fortitude also play a part.

"Once you figure out your target pace, you have to stay at it," Rapoport said in the release. "People sometimes get too excited or change their game plan on the day of the race, and that's a tactical mistake."

 -- Jeannine Stein / Los Angeles Times

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