5 Weird Things Running Every Day Does to Your Body

1. Runner’s Knee

Patellofemoral pain syndrome, also known as runner’s knee, tends to affect runners who try to do too much, too soon, according to Bert Mandelbaum, MD, an orthopedic surgeon and sports medicine specialist at Cedars-Sinai Kerlan-Jobe Institute in Santa Monica, California.

“One of the risks with running is that you increase the chances of getting some type of stress-related injury, because you’re putting additional stress on your bones, tendons, and cartilage, and that includes the knees,” he says.

Runner’s knee causes pain around or just behind the kneecap. If particularly severe, you might feel the pain all the time; if less severe, you may feel it after long periods of sitting with bent knees, running, squatting, or climbing or descending stairs, per research.

What to Do About It You’ll want to stop running until the pain goes away. Then, starting with brisk walking, gradually increase your distance and speed. Dr. Mandelbaum suggests no more than a 10 percent increase per week on each of those variables, but increase distance or speed one at a time, not both simultaneously. (If the pain doesn’t go away after three to five days of no running, it’s time to call your doctor.)

Also, be sure to warm up before running (or any exercise) and incorporate leg-strengthening exercises into your workout routine to strengthen the muscles supporting the knee.

And you may need to change how you run, as your stride could be the main culprit, suggests Carol Mack, DPT, CSCS, a doctor of physical therapy and trainer in Cleveland who often works with runners. Talking with a running coach or physical therapist who can evaluate your body mechanics can often make a big difference in taking pressure off your knee, she says.

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2. Your Toenails Turn Black

What causes the toenails of distance runners to turn black? It’s actually the result of bleeding underneath the nail.

Improperly fitted or too-small footwear is usually the culprit, says Mandelbaum, as well as longer toenails. “When your toenails hit multiple impact points inside the shoe, it can create different points of force — which causes stress on that area,” he says. The excess rubbing stride after stride eventually causes enough damage to bruise or bloody the toes. Wearing the right size shoes, as well as not ramping up training too quickly, can help you avoid the problem, he adds.

What to Do About It Make sure your running shoes fit, your toenails are clipped, and you’re not overtraining. To find the right fit for your running shoes, make sure there is space equal to the width of your thumb between the tip of your big toe and the end of your shoe. If you’ve been diligent about all of these things, and you’re still struggling, try visiting a running store that sells shoes based on assessment of your gait, Mandelbaum suggests. If there isn’t one near you, look online for running-specific stores, since they often have tips on shoe selection.

3. Chafing

Nothing takes the fun out of a long run quite like chafing. It’s the skin irritation that results from skin rubbing on skin (or something else) repeatedly. It’s typically a problem that gets worse when you run for longer distances or longer periods of time. The more rubbing, the more irritation. But heat, moisture, and certain fabrics can all make the problem worse, too.

It’s typical for men who run to experience chafing on their nipples, a sensitive area of skin. Women often experience chafing along the bikini line, also a sensitive skin area (thong-style underwear can make the problem worse). But chafing can certainly occur in other areas, too, like between the thighs, under the arms, or anywhere in the groin area where skin is rubbing against skin or other material.

What to Do About It Rub petroleum jelly or another product specifically designed to address chafing on areas of skin that may chafe, or protect them with bandages. To protect skin around the underwear line, choose clothing made from fabrics with natural wicking properties.

4. Overactive Bladder

Find yourself needing to “go” only a short distance into your run — even though you used the bathroom just beforehand? This could be due to a couple of factors. Increased blood flow from the cardiovascular workout can speed up other body systems as well, including your kidneys’ production of urine.

Also, the urge to pee may not be what it seems. If you’re dehydrated, your body may hold onto this concentrated reserve of urine, creating a sensation similar to the one you get when you have to urinate.

What to Do About It Stay hydrated (especially if it’s warm out or if you’re sweating a lot). Getting plenty of water is essential to a healthy workout. Plan ahead to scope out pit stops along your route, and talk to your doctor if it becomes a consistent issue.

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5. Tummy Trouble

Another potential side effect of dehydration is having gastrointestinal issues, says Mack. Dehydration can alter the way the stomach and digestive system work in a way that will leave your bowels irritable once you start moving a lot on a run, she says. Paying attention to hydrating the day before, as well as during, a long run may help.

Even if you’re well hydrated, you may still have tummy trouble, and it’s common for runners, she adds. As you run, there’s a lot of repeated bouncing of the body and the internal organs, blood flow to the intestines may decrease, and typical production of hormones by the intestines may be interrupted, which may all contribute to GI issues, according to the Mayo Clinic.

“I feel like stress about the run itself doesn’t get as much attention as it should,” Mack adds. “But it often causes digestive issues, too.”

What to Do About It Don’t eat any new-to-you foods before or during a run, and especially not during a race, says Mack. “Not every energy gel, protein bar, or sports drink agrees with every runner’s stomach; and it’s best to find what works before you run,” she suggests.

It’s also best to avoid caffeine for three to six hours before running, and try not to put anything in your stomach for at least two hours before a run, advises the Mayo Clinic.

Another tip: This is the one time you get to skip loading your plate with vegetables. Mack says lots of veggies, whether cooked or raw, tend to increase risk for GI problems during a run.

And if you suspect prerun nerves may be playing a role, try adding meditation or journaling to your prerun routine (either just before you head out or even the day before), Mack says.

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