![]() Oxygen is critical to muscle performance because glucose can only be broken down completely in the presence of oxygen. Aerobic capacity, also known as VO2max, is a measure of how much oxygen the body can transport to the muscles and consume during aerobic exercise. To create his new model, Rapoport identified two fundamental physiological factors that limit performance in endurance runners: aerobic capacity and the ability of the leg muscles to store carbohydrates as glycogen. Once you do that, you need to make sure you appropriately carbo-load.” You need to set a target pace that will get you to the finish without hitting the wall. ![]() “In order to avoid it, you need to know what your capabilities are. “People think hitting the wall is inevitable, but it’s not,” says Rapoport, who has run 18 marathons, including a personal best of 2:55 at this year’s Boston Marathon. When that happens, the runner’s pace can drop about 30 percent, and ketones, the byproducts of fat metabolism, start building up in the body, causing pain and fatigue. Hitting the wall occurs when those stored carbohydrates are completely depleted, forcing the body to start burning fat. A small amount of glucose is also present in the blood. Most of those carbohydrates come from glycogen stored in the liver and in the leg muscles. Of the hundreds of thousands of people who run a marathon each year, more than 40 percent hit the figurative wall, and 1 to 2 percent drop out before finishing.ĭuring strenuous exercise such as running, the body relies on carbohydrates for most of its energy, even though fat stores are usually much larger. You can’t will yourself to run any faster.” “It’s a big psychological letdown, because you feel powerless. “You feel like you’re not going anywhere,” says Rapoport. 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. As he entered Manhattan for the last several miles of the race, his legs just didn’t want to keep up the pace. The Harvard-MIT scientist, Benjamin Rapoport, was inspired by his experience in the 2005 New York Marathon. 21 issue of the journal PLoS Computational Biology, which allows runners to calculate personalized targets using an estimate of their aerobic capacity. The result is a new model, described in the Oct. student in the Harvard-MIT Division of Health Sciences and Technology - has taken a more rigorous approach to calculating just how much carbohydrate a runner needs to fuel himself or herself through 26.2 miles, and what pace that runner can reasonably expect to sustain. Now, one dedicated marathoner - an M.D./Ph.D. Most marathon runners know they need to consume carbohydrates before and during a race, but many don’t have a good fueling strategy.
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