On Sunday, thousands of runners and walkers will endure 26.2 miles on foot to complete the Honolulu Marathon course. The majority of these athletes have spent several months training their bodies for the required endurance. During training, muscles, joints, hearts and lungs strengthened gradually and body fat decreased. This preparation was needed to handle the hours of running required to finish the event, but all that effort shouldn’t end at the finish line.

Question: How long does it take to recover from a marathon?

Answer: It has been estimated that full recovery from a running event takes about one day for every mile of running at one’s personal competitive pace. This recovery period involves a substantial reduction in the extent and intensity of training that gradually returns to normal. So, full recovery after a marathon takes about a month. In contrast, some marathon finishers return to a couch potato lifestyle, and training stops or drops to near nothing.

Q: How quickly does the post-marathon couch potato lose the benefits gained during marathon training?

A: The answer depends on the type of training benefit being considered. During the months of marathon training, the typical changes that occur include a loss of body fat, a drop in blood pressure, improved heart function, increased “good” HDL cholesterol, increased ability to utilize oxygen during exercise, increased capacity to use fat for fuel during exercise, increased insulin sensitivity (which helps to normalize blood glucose levels), and an increased capacity to store carbohydrate and fat in muscles.

Based on a study conducted in the early 1980s with middle-age men, body fat lost during training can return rather quickly when training is stopped. These men completed the Honolulu Marathon Clinic nine-month training program and stopped training after finishing the marathon. They regained all the body fat they had lost (about four pounds) within eight weeks of no training. In other words, a nine-month investment was lost in eight weeks. Men in the study who kept running at a reduced level of about 15 miles per week did not regain any body fat.

Many of the less obvious changes that take place in the body during marathon training also can shift into reverse just as quickly when training is stopped. For example, blood pressure generally increases during detraining, and HDL cholesterol levels drop. The capacity of the heart to pump blood gradually declines. Along with these cardiovascular changes, related changes take place in the lungs and muscles that reduce the ability of the body to utilize oxygen.

Losing marathon fitness also results in a decreased sensitivity to insulin that leads to increased blood glucose levels. The ability of daily exercise to help regulate blood glucose is what makes exercise so beneficial for those with type 2 diabetes or prediabetes. Especially in the early stages of type 2 diabetes, it is now known that the right dose of regular exercise can reverse the condition and often hold it off as long as fitness is maintained. This is one of the main reasons that we are all encouraged to incorporate regular exercise into our lifestyle.

So, once you are trained for a marathon, don’t stop abruptly. The time and effort it takes to maintain the benefits of fitness are much less than what it takes to get back into fitness. Regular exercise has so many health benefits that it is often said that if you could put exercise into a pill, it would be the most frequently prescribed medication in the world.

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Joannie Dobbs, Ph.D., C.N.S., and Alan Titchenal, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.