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Runners Can Now Calculate Calories Needed For Energy

October 22, 2010

A new formula could help runners determine a more exact way to calculate just how many carb calories are needed to stay in a 26.2 mile race before a phenomenon occurs known as “hitting the wall.”

“About 40 percent of marathon runners hit the wall,” Benjamin Rapoport, a student in the Harvard-MIT Division of Health Sciences and Technology, told Reuters Health.

Runners burn up all the carbohydrates stored in their livers and leg muscles, forcing them to slow down dramatically as the body starts to burn fat. 

“You feel like you’re not going anywhere,” Rapoport said in a statement. “You can’t will yourself to run any faster.”

He said many runners believe hitting the wall is inevitable and it is just part of running a marathon.

Rapoport said in a telephone interview with Reuters “that is not true at all.”

“What I came up with was essentially a set of formulas,” he said.

“People need to know really three things: how much they weigh, what their target marathon time is and their maximum oxygen intake capacity,” he said. “That is a measure of a person’s aerobic fitness.”

Aerobic capacity is a measure of how oxygen in the body is transported to the muscles and consumed during aerobic exercise.

That capacity, known as VO2max, requires a treadmill stress test at maximum effort to measure.  However, Rapoport said an informal way to estimate aerobic capacity is to divide your maximum heart rate by your resting heart rate and multiply by 15.  In order to find your maximum heart rate, simply subtract your age in years from 220 beats per minute.

He said the result is a number that tells runners how many excess carb calories they need before participating in a race.

He said many runners also supplement their stores carbohydrates by taking gels and sports beverages as they are running, but a runner is able to carry more fuel in their legs and liver if they know the right amount.

He has built an online calculator to help figure that out.  This way runners are able estimate their aerobic fitness pace and race goals.  The calculator is available for free online.

“It’s my gift to my fellow runners,” he told Reuters.

Rapoport’s study was published Thursday in the journal PLoS Computational Biology

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