Weird, gross and unexpected things that happen when you run

Story highlights

  • Wacky and serious side effects of running, as explained by experts
  • How to deal with nipple chafing, mid-run pooping and black toenails

(CNN)According to Bruce Springsteen and modern research, we were born to run.

In fact, studies (PDF) show that our legs and body mechanics are naturally suited for covering many miles for long periods of time.
But while running may be a natural body movement, the things that happen to us when we run can be downright weird.
    From chafing to more serious issues, experts explain the unexpected side effects of pounding the pavement and what you can do to prevent them.

    Chafing

    Most runners have experienced chafing at some point. When clothing exceedingly rubs against a runner's chest, armpits, thighs or groin, it can be irritating and painful, almost like a rug burn. In severe cases, the friction can be so rough that it creates a fissure on the skin, causing sensitive areas, such as nipples, to bleed.
    That problem even has a clinical term: jogger's nipple.
    "You don't want to be that guy," said Dr. Jordan Metzl, a New York sports medicine doctor who has finished 35 marathons.
    Metzl explained that jogger's nipple happens when a runner's shirt rubs against his exposed chest. To avoid this painful problem, he suggests wearing sweat-wicking tops rather than loose cotton T-shirts. Slathering skin with Vaseline or Body Glide and placing Band-Aids on sensitive areas can also help prevent chafing.
    Thanks to sports bras, women are usually protected from chafing of the chest. However, sports bra straps and athletic pant linings are also prone to rubbing. Often, chafing is exacerbated when clothes get wet, such as when running in the rain. Cold weather can also cause more chafing, Metzl explained, because dry, cold skin is more susceptible to abrasive friction.

    Cold symptoms

    Ever returned from a run with your nose still running? Having a runny nose, a hacking cough or a sore throat after running isn't uncommon, especially in cold months, Metzl says.
    Cold air can constrict airway and nasal passages, and dry air irritates lungs, which need air to have a certain level of humidity. This is why it can be harder to breathe in the winter season than in humid summer months.
    "Sniffles -- snot rockets galore -- and cough were just part of the game when it comes to winter running," said Liam Boylan-Pett, a former middle-distance runner at Columbia.
    Cold-like symptoms from running aren't restricted to outdoor miles. Even indoors, dry air can cause chest tightening and coughing. High school and college runners who compete in indoor track meets often experience scratchy throats and burning lungs from the dry, overheated air in indoor complexes. To help prevent this, stash a bag of cough drops in your gym bag before heading to the track or treadmill.

    Potty problems

    Dr. Jason Karp, an exercise physiologist and author based in San Diego, says bathroom trouble is a hot topic for runners. "It's a real concern," Karp said. "When you're running in a public place with no bathrooms or bushes in sight and you have to poop, what do you do?"
    Having to use the bathroom mid-run, particularly to defecate, is a problem that plagues runners much more than, say, cyclists or swimmers.
    "When you're running, there's a lot of up and down movement going on," Metzl explained. This jostling motion can kick-start muscle contractions in the intestines, moving whatever we had for dinner last night out of our systems.
    "There's extra gravity when you run," Karp added. "It has more of an effect (on your digestion) than if you were biking or swimming." Unfortunately, the urge to poop while running can come at inopportune times: when you're halfway through a run on vacant city streets or you're competing in a marathon with no portable toilets in sight.
    To avoid this problem, Karp advised, "Go to the bathroom, and get everything out of your system before you run." Races usually have portable toilets available near the starting line.
    What you eat and when you eat before running may be the key to a happy gut. Generally, runners should avoid eating high-fiber and high-fat foods too close to running, as these foods tend to linger longer in the intestines -- and may haunt you later.
    "Some runners like to eat more fiber the night before a race or run, to start the digestion process earlier," Metzl said. "You want to be cleaned out before you start running."
    However, there's "no one size fits all" when it comes to nutrition, says Chris Troyanos, medical coordinator of the Boston Marathon. Though some runners eat fiber the night before a race, others tend to load up on carbohydrates, such as heaping plates of pasta. While runners need plenty of energy, stuffing yourself with carbohydrates -- especially if you've never carb-loaded before -- can lead to an upset stomach, Troyanos says.
    "It's important to practice what you eat and drink, before, during and after running," Troyanos said. If you normally have a bowl of oatmeal and a banana before a morning workout, don't try a spicy sausage biscuit the morning of a marathon.

    Blisters and black toenails

    As you find which food best fuels your running, find your perfect fit in running shoes. Dr. Stuart Weiss, medical director of the New York City marathon, says new runners commonly complain of joint pain and muscle soreness.
    "I'll ask, 'What's going on here?' " Weiss said. "Usually, it's bad shoes."
    To find a well-fitting pair of shoes, Weiss tells new runners to visit a running store for a proper foot measurement and a gait analysis test, which is performed on a treadmill. Knowing a runner's foot shape and size, as well as his running mechanics, is crucial to picking out the right pair -- and may seriously decrease injury risk.
    Among the injuries that can be triggered, blisters and black toenails are classic consequences of too-small shoes. Karp explains that when you run, your feet swell a bit, and your toes can rub against the top of your shoes. Constant rubbing can create blood blisters beneath the toenails, giving the appearance of black nails. In some cases, toenails can be pried off completely.
    "You want ample room in the toe box of your shoes," Karp said. Being sure to trim toenails and wear good-quality socks can also help avoid black toenails, he says.

    Serious issues

    Although black toenails can be irritating, there are more serious issues runners sometimes deal with. At marathons, Troyanos has witnessed several medical emergencies, many of which he says could have been prevented.
    "Running a marathon is inherently a safe exercise," Troyanos said. "When people don't prepare, there's a potential risk."
    For example, at the 2012 Boston Marathon, the temperature soared to 86 degrees, and runners who weren't prepared for the heat suffered heat exhaustion and dehydration, he said.
    Mark Beams, a former runner for the University of Michigan track and cross-country teams, had a heat-related incident on the track in 2014. During a 10,000-meter race at his regional meet in Jacksonville, Florida, his legs began to buckle.
    "I remember stumbling and hitting the track and thinking, 'Well, that's weird,' " Beams said. In his last two laps, he fell three or four more times. He remembers falling, but he can't recall what happened between the falls or what happened after the race. "My memory is pretty spotty," he said. "I don't remember crossing the line."
    Hours later, Beams learned that he had collapsed right before the finish line. "I was in and out of it, and I couldn't hold my head up," he said. He had a dangerously fast heart rate of 212 beats per minute, even 10 minutes after the race.
    He was covered with ice packs, laid on a stretcher and sent to a nearby hospital, where he received 4 liters of IV fluids. "I was overheating," Beams said. "My body shut down."
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    "As an athlete, you have to know your limitations," Troyanos said. He emphasizes that every runner is different: One runner's training, diet and hydration plan may work perfectly for him but maybe not for anyone else.
    "You have to listen to your body," Weiss agreed. "When people are out of it after a race, they haven't listened to their bodies."
    Troyanos added, "You have to ask (yourself), 'What's the responsibility of the runner?' 'Are you really prepared?' The stress a body takes when running is significant."