Here's What Running Marathons Does to Your Body

Women running marathon

Getty Images / Leo Patrizi 

If you’ve seen enough inspirational photos on your Instagram feed of friends completing marathons, or are bored with your spinning routine, you might find yourself wondering if it’s time to hop on the marathon bandwagon yourself. After all, running seems like a positive "trend" to jump on, since it gets your heart pumping, your muscles moving, and your lungs breathing in the fresh outdoor air. However, pounding the pavement (or trail, track, or treadmill) for so many miles has us wondering if there are any serious bodily risks involved.

To get to the bottom of the potential risks and benefits of marathon training, we turned to two running experts.

Meet the Expert

Jonathan Cane is an exercise physiologist and certified running coach. He has been coaching marathon runners for over 30 years, and is the author Triathlon Anatomy ($19).


John Rowley is a certified personal trainer, the ISSA director of wellness, the founder of UX3 Nutrition, and the best-selling author of The Positive Power of Fitness ($16).

The Potential Risks

Let’s get the bad news out of the way first. While Cane and Rowley shared that there are definite benefits to training for and running marathons, there are a handful of risks and consequences as well. But before you nix the idea of putting “running a marathon” on your bucket list, stick with us. Our experts have some great advice on mitigating the potential risks.

It can cause musculoskeletal injuries.

According to Rowley, by far the most common downside of logging so many miles is that it causes a significant amount of wear and tear on joints and muscles because of the frequent and heavy impact. A research review of risk factors for running injuries found evidence suggesting a correlation between a history of previous injuries and a higher risk of incurring new ones from running. Runners who previously suffered overuse injuries should be sure to address and correct whatever factors led to that injury—be it improper footwear, overly aggressive training, muscle imbalances, or nutritional deficiencies. Failing to remedy the root cause is a recipe for a recurrence.

Even though running injuries are common during marathon training, there are several steps you should take to minimize your risk. The first is to train smartly. Runners who do too much too soon, overdo it in general, or train too sporadically are all at increased risk for musculoskeletal injuries. The body needs time to adapt to training, and recovery and rest are also critical for tissue repair. Make sure you work with a coach or get a proper training plan.

Secondly, make sure you warm up for your training runs and races. "Instead of starting in a full-out sprint, give yourself some time to gain better range of motion and momentum—once you feel your body is acclimated to a comfortable speed, you can then start to push yourself a little more to avoid injury,” Rowley says. He also urges all runners to stretch. "You're less likely to encounter injury while running if you've prepped your muscles with a good stretch." 

Thirdly, make sure your shoes fit properly and are changed every 350-500 miles to ensure they still provide the support and cushioning you need.

Lastly, Rowley recommends eating a diet full of lean protein, complex carbohydrates, and fresh greens, as well as plenty of water. It’s also important to get enough calories to help your tissues rebuild.

It can cause muscle soreness.

To the uninitiated, it might seem like marathoners like their lingo almost as much as the post-race brunch. After all, it shows you’re part of the special 26.2-mile club. If you’re thinking of becoming a card-carrying member, one of the terms you should be familiar with is DOMS, which is an acronym that stands for Delayed Onset Muscle Soreness. While popular thought used to be that DOMS was the result of lactic acid in the muscles, this is not true (lactic acid is metabolized and removed).

“In most cases, DOMS is due to microscopic tearing of muscle tissue. It's usually worse after hard runs, and especially so after downhill running,” explains Cane. “Being attentive to post-run nutrition can help decrease the effect or duration of the soreness, so be sure to get some protein, complemented by carbohydrate shortly after the run.”

“If you're having trouble differentiating between ‘normal’ muscle soreness and injury, keep in mind that DOMS usually sets in the day after a run, gets worse the second day, and [then] starts to ease up,” says Cane. “If your pain is not following that pattern, [or] is sharp or radiating, it may be indicative of something more substantial.”

You might lose a toenail (or two!).

You might need to put your favorite pedicurist on speed dial once you start marathon training. Though certainly the gravity of black toenails or even toenail loss pales in comparison to true injuries, toenail maladies are so ubiquitous among marathon runners that there are memes declaring them a rite of passage. 

“To a certain extent, it's just the nature of the beast; your toes contact the inside of your shoe thousands (if not tens of thousands) of times in each run,” explains Cane. “Even a subtle rub adds up when multiplied over days, weeks, months. That repeated contact can lead to blood forming under the nail, which in turn can lead to the nail falling off.” If only the tooth fairy could recruit a running toenail fairy...

The good news is that while some degree of microtrauma is inevitable, you can reduce your risk, should you decide you’re perfectly fine skipping this rite of passage. “First, cut those toenails short. The shorter they are, the less contact there will be with the shoe,” advises Cane. “Second, make sure your shoes fit properly. Sure, some of this is inevitable, but if it's happening often, it's likely that the shoes don't fit properly. Along those same lines, experiment with different sock thicknesses.”

It may cause harm to your kidneys.

Most people don't immediately think of kidney damage when they think of the common risks of marathon running. However, according to research conducted at the Yale University School of Medicine, 82% of marathoners experienced acute injury (AKI). AKI affects the kidneys' ability to filter waste from the blood and balance fluids and electrolytes. Fortunately, this condition typically resolves within 48 hours with proper rehydration. A subsequent study found that runners who experienced AKI during a marathon were particularly heavy sweaters, losing approximately four liters during the race—two liters more than marathoners without AKI. According to Cane, with proper race hydration, including the ever-important electrolytes such as sodium and potassium, it should be possible for all runners to avoid AKI.

It may not be effective for weight loss (should that be your goal).

Logging many miles does burn calories, since the average person burns roughly 100 calories every mile they cover. However, if you think that marathon running is you ticket to quick-and-easy weight loss, you might be surprised. "While lots of running is a great way to build endurance, it does slow down your metabolism since you're technically losing muscle," Rowley says. In other words, running consistently depletes the calories needed for sustaining muscle mass, and it’s muscle mass that most significantly dictates your metabolic rate.

Additionally, many people experience a significant increase in their appetite after they start marathon training. The body needs fuel for the run and for proper recovery. It's often the case that the calories burned during a long run are (and should be) replaced after the sneakers come off.

It can weaken your immune system.

”After particularly challenging runs, your immune system is suppressed, and you're more susceptible to illness,” says Cane. “That's certainly not a reason to avoid running, but it is justification to avoid hard efforts if you're already feeling compromised or might be exposed to contagions.” Fortunately, if you listen to your body and skip your run when you feel a sore throat coming on or feel worn down, your immune system should be able to fend off any illnesses during your marathon training. After all, getting regular exercise has been shown to correlate to a more robust immune system. Just don’t overdo it.

The Potential Rewards

Marathoning also has many upsides, which is probably why over a million people around the world toe the starting line for a marathon every year. “Running, and exercise in general, has countless health benefits that go well beyond being able to run faster,” notes Cane. Let’s dig into some of these benefits.

It's good for your cardiovascular health.

Marathon running has been shown to improve markers of cardiovascular health. For example, research has shown that it can decrease blood pressure and resting heart rate. It may also reverse the aortic stiffening process that naturally occurs with aging. And because aortic stiffening is associated with increased risk of cardiovascular events, this means running marathons may keep your ticker healthily ticking along.

It produces mood-lifting endorphins.

If you've heard of the notorious "runner's high," you are likely aware that running for long periods of time can bring on feelings of euphoria. This happy feeling is the result of endorphins, the natural, feel-good hormones produced by the body. Even though Cane says "the so-called 'runner's high' is as elusive as a yeti for most runners," distance running, like most exercise, produces endorphins, so you're apt to feel happier, less stressed, and experience less pain for a period of time during and after a long run.

It can improves mental health

Beyond just the short-term, mood-boosting power of endorphins, training for and completing a marathon can improve your mental health overall. Running can build a sense of confidence and self-efficacy, “Running a marathon was the best thing I’ve ever done for myself. I have struggled with depression since I was a young teenager and have had a very hard time finding a sense of self-worth,” shares marathon runner Nicole Fisher. “I always felt like anything I had succeeded in couldn’t be that hard if I’d done it. When I finished my marathon, for the first time, I had irrefutable proof that I had done something extraordinary.” What’s even better is that this feeling of accomplishment and self-efficacy has lasted long after the race medal went up on Fisher’s wall. “While I’ve still had ups and downs with my mental health, I like myself now even when I’m down. I know the strength inside of me and the determination,” says Fisher proudly “I know it sounds insane, but it immediately changed my view of myself and what I can do.”

It is relatively accessible.

Besides needing a good pair of shoes (though some runners still swear that barefoot is the way to go), running doesn’t require a lot of special, expensive equipment. Sure, there are all sorts of accessories, cute clothes, and training gadgets you can buy if you have the desire and means, but overall, running is a relatively affordable hobby. Marathon entry fees can cost upwards of $200 for some of the most popular big-city races, but you can save money by opting for a smaller, local race and registering well in advance.

You—yes, you—can do it.

Although it’s undoubtedly an impressive feat, running a marathon is actually possible for most people. There are even avenues for runners with physical impairments, such as Achilles International for vision-impaired runners and Prosthetic Running for runners with limb loss. You also don’t have to have to look a certain way, and it’s never too late to start. Take it from Nancy Morgan Scholl: “I used to be overweight and inactive. I hated to sweat,” Scholl admits. “I started to run/walk when I was 50 and ran my first marathon at [age] 57.” Nearly a dozen marathons later, she says, “I feel so much better about myself, mostly because of the commitment that I have maintained toward good health for 14 years.”

Doretha Walker, who ran her first marathon at age 46, shares the positive aftermath of the lasting pride she gained by finishing such a challenging endeavor: “[Since then], whenever things got bad I would whisper to myself ‘you ran a freaking marathon, you can do this’—and I proceeded to do the thing, whatever it was. And after eight more marathons, I still whisper that to myself because sometimes life is hard,” shares Walker. “Those words have gotten me through three triathlons, getting my PhD, a few breakups, losing my job, a move to another state, deaths of loved ones, and a host of other things. No matter what comes my way, I know that I can do it.”

Article Sources
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  3. Mansour, Sherry & Martin, Thomas & Obeid, Wassim & Pata, Rachel & Myrick, Karen & Kukova, Lidiya & Jia, Yaqi & Bjornstad, Petter & El-Khoury, Joe & Parikh, Chirag. (2019). The Role of Volume Regulation and Thermoregulation in AKI during Marathon Running. Clinical Journal of the American Society of Nephrology. 14.

  4. Anish N. Bhuva, Andrew D’Silva, Camilla Torlasco, Siana Jones, Niromila Nadarajan, Jet Van Zalen, Nish Chaturvedi, Guy Lloyd, Sanjay Sharma, James C. Moon, Alun D. Hughes, Charlotte H. Manisty. (2020). Training for a First-Time Marathon Reverses Age-Related Aortic Stiffening. Journal of the American College of Cardiology, Volume 75, Issue 1, Pages 60-71.

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