The Science of Marathon Running

Completing the Boston Marathon is a feat of speed and endurance. One sprint across the finish line represents months, if not years, of diligent training. 

Maybe you’d like to join those athletes one day, or maybe you’d just love to get off the couch and complete a 5k. The good news is, almost any physically healthy person can take up running, says Roger Fielding, associate director of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts and leader and senior scientist of the Nutrition, Exercise Physiology, and Sarcopenia (NEPS) team. 

It offers a host of health benefits, too.

“Running is one of several types of activity that uses a lot of the large muscle groups in our body. It can be performed at an intensity that causes our cardiovascular system to be activated. It raises our heart rates and allows for the cardiovascular system to do its job: pump lots of blood to our working muscles,” says Fielding, who’s completed a few half-marathons himself.

When you start running a marathon, muscles have to adapt and maximize their internal storage of carbohydrate, known as muscle glycogen. As the marathon progresses, these stores become depleted, resulting in fatigue or exhaustion. Boston’s many downhill sections also cause lengthening or eccentric contractions, which can lead to muscle damage and soreness that require days or weeks of recovery.

Beyond muscle maintenance, cardiovascular fitness when running is key: To complete a marathon, you need to be able to run at between 50 to 70 percent of your maximal aerobic capacity for upward of three to five hours. Also known as VO2max, maximal aerobic capacity is the “gold standard” for cardiorespiratory fitness, Fielding says. Usually measured on a treadmill, this is the maximum amount of oxygen a person can consume per minute during intense exercise. Essentially, this reflects how well your heart and blood vessels can pump and deliver oxygen, and how effectively your working muscles extract that oxygen. Values vary depending on sex, age, weight, genetics, and fitness level.

This won’t happen overnight. It’s important to build gradually to avoid injury. Here’s how to get started, at any age.

20s and 30s

Cardiac fitness is at its peak right now (and decreases by 1 percent each year–another indignity of aging!), so this is prime time to lace up your shoes. But even young people should start with low-intensity, shorter runs, Fielding urges. 

“As your body adapts, you can increase both the duration or distance that you’re running, and start to think about increasing the intensity or speed,” he says.

Fielding says that overenthusiastic young runners often think they can run through injuries, such as shin splints or knee or hip pain, exacerbating arthritis.

Durations and distances are highly individual, but no matter what: “The one thing I always tell people is make sure that you don't overtrain and you don't do anything to get injured,” he warns. 

40s and 50s

By now, it might take a bit longer to build muscle and to recover from each run.

Fielding says that all middle-aged people, runners or not, should strive for 150 minutes of moderate to vigorous physical activity per week. Training for a marathon requires even more activity, depending on baseline fitness, but that’s a good place to start.

And take heart (literally): small amounts of exercise matter, even if they won’t prepare you for a full marathon.

“Even if you go from being sedentary to walking 15 or 20 minutes every day, that health benefit is really important,” he says.

If you have cardiovascular risk factors such as hypertension, diabetes, or elevated blood cholesterol, check with your doctor before training. 

50s and up

First, the good news: “You're never too old to run a marathon, but you have to go into the race being in the right cardiovascular and endurance condition,” Fielding says.

At this stage, it could take roughly six to 12 months of training to prepare for the rigors of 26.2 miles. It’s important to mix training with plenty of recovery periods (which will differ for each individual), and to check with a doctor to ensure cardiovascular fitness.

Older people’s muscles are also vulnerable to sarcopenia, an age-related syndrome where muscle mass declines.

With sarcopenia, “the actual size and cross-sectional area of individual muscle cells and fibers decreases. In addition to that, there are well-described decreases in the maximal voluntary strength that those muscles can generate,” he explains.

It’s possible to ward off sarcopenia with structured programs in strength training. Protein supplements could also promote gains in muscle mass when combined with exercise.

The Key: Hydration

Last but not least: Hydration is key, whether you’re 25 or 75.

“As people exercise, they sweat and dissipate heat through our body’s evaporative, sweating mechanisms. They lose body water. If you don't adequately replace those sweat losses with fluid intake, you can actually get into a very serious situation with either heat exhaustion or heat stroke,” he warns.

According to the National Academy of Science, men need 15.5 cups of water per day, while women should aim for 11.5 cups. Fielding also recommends solutions with both fluid and carbohydrates, such as Pedialyte or Gatorade. The small intestine absorbs them quickly, leading to faster rehydration. 

And, even if you’re not ready to pound the pavement, maintaining muscle strength is a requisite part of long-term health.

“It may improve the quality of your life and increase what we think about as your health span, or the number of years that you live disease-free or independently. Muscle strength is a really important component of maintaining a person's independence as they age,” Fielding says.

And aerobic exercise—in most any form—is important for younger folks, too. “Gains in aerobic fitness and strength have multiple health benefits at most ages, including improvement in blood pressure … positive effects on mental capacity, reduced risk of cardiovascular disease and many types of cancer, better sleep, and improved glucose tolerance,” Fielding says.

Best of all?

“These benefits occur even with more modest amounts of training. You don’t have to train for a marathon,” he says.