By Richard AlleyneThe researcher has worked out a mathematical model that calculates how much carbohydrate each individual runner needs to eat in order to stop their body reserves running out during the race.
Hitting the wall occurs when those stored carbohydrates are completely depleted, forcing the body to start burning fat.
When that happens, the runner's pace can drop about a third and byproducts from the fat, start building up in the body, causing pain and fatigue – and often forcing runners to pull up.
Runners often think this is an inevitable hurdle to jump but according to Benjamin Rapoport, a medical student at Harvard, proper planning means it should never happen.
"Hundreds of thousands of people run marathons a year and 40 per cent of them hit the wall," he said.
"That is not necessary and with this formula you should not hit it again.
"The wall is not inevitable if you run at the right speed and prepare with the right food you should not hit it," he said.
"At the moment there are rules of thumb that people follow but they are just not accurate enough. That is because there is no such thing as an average runner."
Mr Rapoport has come up with the Marathon Formula which uses simple factors such as body weight, age, resting heart beat and fitness levels, to work out range of times that can be achieved and how best to "load up on carbs" before the 26.2 mile race.
The amateur runner was inspired by his experience in the 2005 New York Marathon.
As he entered the last few miles of the race, his legs just didn't want to keep up the pace.
He was experiencing a common phenomenon among marathoners, known as "hitting the wall." Essentially, the body runs out of fuel, forcing the runner to slow down dramatically.
"You feel like you're not going anywhere," said Mr Rapoport.
"It's a big psychological let-down, because you feel powerless. You can't will yourself to run any faster."
Of the hundreds of thousands of people who run a marathon each year, more than 40 per cent hit the figurative wall, and one to two per cent drop out before finishing.
During strenuous exercise such as running, the body relies on carbohydrates for most of its energy, even though fat stores are usually much larger.
Leg muscles can be saturated with carbohydrate between 36 and 12 hours before the race.
Using the calculator, which is available online, an 11 stone man, who is 35 years-old and wants to run 4 hours, 30 mins, is told to eat 1,600 calories of carbohydrate – eight bowls of rice or five of pasta, in addition to their normal diet before the race.
If he wants to faster, it calculates he should eat 3,000 calories – 15 bowls of rice or 10 of pasta.
"People think hitting the wall is inevitable, but it's not," said Mr Rapoport, who has run 18 marathons, including a personal best of 2:55 at this year's Boston Marathon.
"In order to avoid it, you need to know what your capabilities are. You need to set a target pace that will get you to the finish without hitting the wall.
"Once you do that, you need to make sure you appropriately carbo-load."
To create his new model, Mr Rapoport identified two fundamental physiologic factors that limit performance in endurance runners: aerobic capacity and the ability of the leg muscles to store carbohydrates as a substance called glycogen.
Aerobic capacity is a measure of how much oxygen the body can transport to the muscles and consume during aerobic exercise. Oxygen is critical to muscle performance because glucose can only be broken down completely in the presence of oxygen.
The journal PLoS Computational Biology.
Aerobic capacity can be measured by measuring resting heart rate or when running at a constant pace on a treadmill.
The model's predictions also depend on the runner's leg muscle mass, because larger muscles can store more glycogen. Leg muscles make up about 21 per cent of body mass.
One of the most important things a runner should do during a marathon is stick to his or her target pace, Mr Rapoport said.
"When runners start out too fast, they burn a higher percentage of carbohydrates, increasing the risk of hitting the wall.
"Once you figure out your target pace, you have to stay at it," he said.
"People sometimes get too excited or change their game plan on the day of the race, and that's a tactical mistake."
The Marathon Formula calculator can be accessed at endurancecalculator.com.
The Formula
Mc =dmfc (i)
Carbs needed (Mc) = distance in kilometres (d) X weight in kilograms (m) X intensity factor (fc(i)) *
*This is how fit you are and how hard you are pushing your body
Example:
For an averagely fit, 11 stone runner aged 35
The Marathon Formula calculates that to run 4 hours 35 mins he needs to eat 1,546 calories of carbohydrate (eight servings of pasta or 10 of rice) 36 hours to 12 hours before the race. (This is on top of normal meals)
To run 3 hours 10 mins need to eat 2,900 calories (15 servings of pasta or 20 of rice)
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