18 Weird Ways Running Affects Your Body

Answering the “why” behind twitchy legs, black toenails, and an urgent need to find a bathroom.

Dimity McDowell |

Runners know bodies.

We understand what training does for our legs, lungs, and heart. We’re also intimately familiar with the other, less attractive ways running impacts our bodies. But we don’t necessarily know why we have to pee even though the shrubs got watered just two kilometres ago. Or why our knees crackle and pop as we go down stairs. Or why someone way heavier can kick our skinny butts in a half marathon.

So Runner’s World consulted doctors, physiologists, nutritionists, and other experts, and frankly asked them the most quirky and perplexing questions about the bodies we know and love. We also asked for practical advice about how to deal with our issues. Here’s what the experts said.

Jesse Lefkowitz

1. How can someone just as short/tall/skinny/fat as me run so much faster?

Plenty of reasons why your doppelganger leaves you in the dust. Speedwork may be his religion, and you haven’t converted yet. This may be her 50th 10K, when you’re just stepping up to the distance. He may have a new girlfriend standing on the sidelines; she may have a post-pregnancy goal she’s gunning for.

RELATED: 8 Tips For Running During and After Pregnancy

“Just because two people are long and lean or have a powerful build doesn’t mean they match up in terms of VO2 max, mental toughness, or injury history,” says Kristen Dieffenbach, associate professor of athletic coaching education at West Virginia University. Many performance components, such as endurance, pace, turnover, and mental toughness, can be improved with planned, systematic training, except for one very significant one: genetics. “Muscle-fiber type and VO2 max are genetic,” says Jay Dicharry, director of the REP Lab in Bend, Oregon. “That’s how some people who don’t even train can blow by you on race day.”

Running Rx: You can’t change your genetic destiny, but you can greatly influence your performance by training smart, adding speedwork, tempo runs, running-specific drills, and strength training to your routine. Plus, remember there’s a reason it’s called a PR: Beat it – not yourself – up.

2. Why does my GI tract act up when I’m running?

Some people get headaches when they’re stressed. Runners get the trots.

A 2008 study on 1,281 Dutch runners found that at least 45 percent complained of some gastro-related issue during the run.

RELATED: 15 Tips For Avoiding Runner’s Trots!

“The GI tract is very sensitive to stress, and running – or the anticipation before a race – is definitely stressful,” says Darrin Bright, family physician and sports medicine specialist in Columbus, Ohio. When you run, your intestines take a double hit: The motion jostles their contents and speeds things along. Plus, blood, essential for your tract to stay on track, is rerouted to vital organs and muscles in your lower half, disrupting the sensitive balance your body has for fluid absorption and possibly causing dehydration, which can lead to cramps that force you to beeline for the bathroom.

Running Rx: Bright recommends putting the stop on bathroom-inducing high-fibre and high-fat foods 24 hours before a race or long run, and fuelling up on benign, already-tested, plain meals.

3. Why do I get so antsy during a pre-race taper?

That two-week-ish span where you cut back training volume by about 50 percent gives you time to recover and to become mentally and physically stronger. You probably haven’t felt well-rested in weeks.

RELATED: Three Ways to Calm Taper Anxiety

“Runners typically aren’t used to having all that energy,” said Larry McDaniel, associate professor of physical education at Dakota State University in Madison, South Dakota. “The body gets accustomed to fatigue as a ‘normal’ state.” Your mind is probably on overdrive, too, thinking about your highly anticipated race day. “A fresh body, coupled with nerves and excitement, can drive you – and those around you – crazy.”

Running Rx: Take 10 minutes to visualise the race, and then try not to think about it for the rest of the day. See a movie (avoid Chariots of Fire); read a book (stay away from Born to Run); grab a beer with a non-running friend; do some gentle exercise if you must.

4. Why do the nipples of some male runners bleed during a marathon, but those of females don’t?

Sweat is a mix of water, salt, and a handful of other minerals. When the water evaporates, you’re left with abrasive salt on your nipples, which are front-and-centre in a high-sweat zone.

“After a few hours, a shirt rubbing against that salt feels like sandpaper,” says Bright, adding that beginner male runners are most susceptible because men typically sweat more than women, and novices take longer to complete a race. The abrasion causes chafing, which causes bleeding, which causes red stripes down the front of a white shirt, especially near the end of marathons. Women aren’t immune. Even nursing moms can be afflicted. “The skin around your nipples isn’t capable of thickening and getting stronger,” says Bright, medical director for the Columbus Marathon. The few women he has seen with bloody nipples were wearing no bra, a poorly fitting bra, or a cotton one.

RELATED: How to Prevent & Treat Chafing

Running Rx: Stay hydrated. “When you stop sweating, all you have left on your skin is salt,” says Bright. “The liquid takes the edge off the salt.” Equipment fixes for men: Protect your teats with circular Band-Aids. Women? A moisture-wicking, properly fitted sports bra.

Jesse Lefkowitz

5. Why does the inside of one ankle get bloody from being hit by the opposite heel, but not the other?

That red tattoo is called a heel whip, and it’s from excessive rotational motion of your foot. Instead of your foot traveling in a forward plane, it makes an arc, causing your heel to nick your anklebone. It doesn’t have to be gory: Heel whips can also just dirty your inside shin.

“The extra torsion can be caused by anything from the alignment in your ankle to a hip issue,” says Dicharry, who adds that one side usually bears the bloody brunt because of muscular imbalances.

Running Rx: Think about pushing off through the big toe, not the pinky toe, so that your foot swings cleanly forward, and you’ll whip your ankle less. If you need more than just a Band-Aid after a run (e.g., ice packs and Advil for various parts of your lower body), a visit to a physical therapist will help you determine whether you have strength imbalances that can be corrected with single-leg exercises.

6. Why do my legs shake after a hard run?

If your rubbery, burned-out gams had a fuel gauge, it would be firmly on “E.” For beginners, the needle may arrive there as a result of sheer effort.

“If your muscles aren’t familiar with a new movement, they become inefficient at contracting and can’t work in a coordinated manner, which results in shaking,” says Michele Olson, professor of exercise science at Auburn University in Montgomery, Alabama. (Veteran runners might experience this phenomenon when they attempt push-ups on feeble arms.) For others, it could be that you started too quickly.

“When you go out too hard, the oxidative system doesn’t kick in as smoothly as it does when you warm up and work up to a pace,” McDaniel says. “It’s like shifting gears too quickly in a car. You deplete your energy levels prematurely.” The other cause is simply that your muscles are depleted of electrolytes and glycogen – easily accessible fuel on which they run – and the shaking is their way of telling you to fill ‘em up.

RELATED: The 5-Minute Warm-Up You Should Be Doing!

Running Rx: Warming up pre-run is key for beginners and vets. Start slow, and ease into your ultimate goal pace. If you’re running hard for more than 45 minutes, drink eight ounces of sports drink about 20 minutes before you run; the carbs will keep your muscles humming. Post-run, if you’re trying to shake the shakes, walk around, stretch gently, and grab quick fuel, like a sports drink.

Jesse Lefkowitz

7. Why does coffee speed up more than just my legs?

A pre-run pre-req for many runners to clear the system on their own terms, java stimulates the muscles in the GI tract faster than Mother Nature; some reports say coffee jolts your system in as little as four minutes. Once you’re out on the road, proceed with caution: Many energy gels have caffeine in them, which may cause your intestines to move as quickly as your legs.

Running Rx: In the weeks before an important run or race, determine how much coffee you need for an evac, then sip and lighten your load accordingly. Also, figure out if you can tolerate caffeinated gels. Plan B: Pick a route with a few public restrooms along the way, so you can properly do your business.

8. Why do I feel nauseated after a long run?

You put in 28 kilometres to be able to eat a burger, not to feel pukey thinking about one. Blame the decreased appetite on chemistry; a 2008 study published in the American Journal of Physiology found that a 60-minute session of treadmill running increased the amount of the gut hormone peptide YY, an appetite suppressant, and suppressed acylated ghrelin, an appetite stimulant. Full-on nausea? “There’s a good probability you haven’t fuelled properly during the run,” says Ilana Katz, a sports nutritionist in Atlanta. A lack of fuel in your body sends it into a stressed mode, that fight-or-flight mentality where survival – not eating rice, beans, and guac – is key.

Running Rx: Try to prevent the problem by taking in about 60 grams of carbs per hour, either through a sports drink, gel, or regular food during your run. “The body can process about one gram of carbs per minute,” says Katz. Post-run, try to knock back something easy, like a recovery drink, within 30 minutes. If you can’t eat right away, don’t worry too much. “Appetite loss is typically short-lived,” says Katz. “Within an hour or two, suddenly you’ll have a major one.”

9. Why do I get headaches during or after a run?

It’s not just because you know you’re returning to the mess you ran away from. Headaches stem from a range of causes, from simple (a too-tight hat) to complex (a proclivity for migraines). Two of the most common reasons are tight muscles and poor hydration. “The trapezius attaches high on your scalp, so if you hold a lot of tension in your upper body as you run, your head could ache,” says Bright. Headaches are also a symptom of both underdrinking and overdrinking.

RELATED: 5 Hydration Mistakes You Are Probably Making

Running Rx: Shake out your arms and hands and teeter-totter your neck as you run. At home, hold your left ear toward your left shoulder, right toward your right; repeat with the chin. Nail your beverage needs by weighing yourself before and after an hour run (without drinking).

Jesse Lefkowitz

10. Why do my bending knees sound like Rice Krispies when I walk down the stairs?

Snap, crackle, pop? Crepitus, the medical term, happens when cartilage, the connective tissue between bones, starts to age, says James Wyrick, orthopedic surgeon and associate professor at the University of Cincinnati in Ohio. We all start life with quiet, smooth cartilage between our kneecaps and thigh bones, but over time, it becomes gray and old and doesn’t regenerate; most people older than age 30 have some mild crepitus. Weak quads or a tight IT band can pull the kneecaps out of alignment and exacerbate the wear and tear.

RELATED: 3 Steps To Beating ITB!

Your knees pipe up when they bend past 30 degrees because the kneecap tracks into a groove in your femur – that is, cartilage-weak bone grinds into cartilage-weak bone. “The intensity of the pressure and the different contact points in the groove make the noise,” says Dicharry.

Running Rx: Cracking knees may lead to problems down the line, like arthritis,” says Dicharry. Minimise that chance by strengthening the muscles that control the hips and knees, and keep your lower half in alignment, such as clamshells for the hip; squats for the knees.

11. Why is it easier for me to run in the morning and so hard to rally at the end of the day – or vice versa?

Your natural bird persona – lark or owl – is partly determined by genetics. Housed in the hypothalamus, the portion of the brain that also controls sex drive and appetite, your biological clock is difficult to alter. If your forebears coherently discussed the Middle East situation at 7 a.m., you’re likely to feel sharp before the sun comes up, too. If they thought 9 p.m. was the perfect time for dinner, you probably are happy staying up late. “Natural morning people seem to hit their lowest body temperature earlier in the night than evening people do,” says Chris Kline, an exercise physiology researcher at the University of Pittsburgh who specializes in sleep research. “Their body temperature is warmer when they wake up, so they’re much more ready to go.”

RELATED: 6 Foolproof Ways To Become A Morning Runner!

But even early birds aren’t primed to perform at sunrise. “Typically, aerobic capacity is slightly lower in the morning because of a lower core temperature and lower levels of hormones that affect performance,” says Matt Fitzgerald, coauthor of The Runner’s Body: How the Latest Science Can Help You Run Stronger, Longer, and Faster. In the late afternoon, the body is naturally the strongest and most flexible it’ll be all day, plus your aerobic capacity is at its highest. “Emotional moods and motivation have been shown to peak in the late afternoon,” says Kline. “Nobody really knows why, but people are typically more willing to push themselves harder in the afternoon.”

Running Rx: If you want to hit the track at 6 a.m. – and not hit anybody there over the head with a coffee cup – expose yourself to light, the easiest way to wake up your body, as soon as the alarm goes off. Also, realise that as you age, you naturally become more of a lark. Want to extend your staying power? Exercise either outside, if the sun is still out, or in a bright room two to four hours before bed.

12. Why am I so sore after a marathon, when I’ve done 35-kilometre training runs?

Did you do your training runs with crowds yelling at you and competitors around you unconsciously prompting you to run faster? Thought not. Whether you’re a 2:30 or a 5:30 marathoner, your race-day pace tends to be at least a smidge – and possibly lots – faster than training days. That’s the difference, says Bright, between being pleasantly and painfully sore. “You accumulate lactic acid in your muscles by pushing the pace, which brings on premature fatigue,” says Bright. “Plus, the extra mileage – very few people do a 42.2-kilometre training run – causes more micro tears in your muscles, and it’s likely your muscles haven’t totally healed from your training. Race day, they get even more beat up.” The combination nets marathonitis, an acute condition that demands stairs be taken backward and the size of a stride be cut in half.

Running Rx: A huge fan of ice baths, Bright recommends the anti-inflammatory plunge, post-race, for at least five to 10 minutes. Don’t bother taking anti-inflammatories. “The newer studies show they really don’t do that much for inflammation,” says Dr. Bright. “And they can potentially put your kidneys at risk.”

Jesse Lefkowitz

13. Why do my legs twitch in bed at night after I’ve run that day?

If your legs are still moving when you’re under the covers, chances are you skimped on a post-run meal. “When you work hard and sweat, you excrete a lot of sodium and calcium, two electrolytes that are responsible for muscle relaxation,” says Olson. “Being iron deficient, especially for women, can also contribute.

Running Rx: Get up and head to the kitchen for a glass of milk and some salty biscuits. To stave off future problems, make sure to include dairy, salt, and iron, found in lean red meat and spinach, in your meals after a run.

Jesse Lefkowitz

14. Why do my toenails go black?

“For regular runners, a black toenail is not a matter of if, it’s when,” says Bright. Three causes of the black badge: a too-short shoe; a toenail that comes into contact with the roof of the shoe too often; and a runner who uses his toes to grip too hard. However it happens, the result is the same. Blood vessels under the nail break open, which spill blood (which looks black under the opaque nail) into the area between the toe bed and the toenail. “That area isn’t accommodating to blood collection: It’s rigid and restrictive,” says Bright. “It builds up a lot of pressure quickly.”

RELATED: 5 Causes of Black Toenails – Identify The Harmless From The Harmful

Running Rx: If the pressure is bothering you and you can handle more hurt, press the end of a paper clip or safety pin, heated with a match, through the nail. “That’s a pretty painful proposition,” says Bright, who recommends the gentler touch of a doctor. Do it sooner, while the blood is still fluid. If the pain decreases and doesn’t bother you, no need to take action. Either way, the skin below it will heal, the nail will die and fall off. Don’t worry, it’ll grow back someday.

Jesse Lefkowitz

15. Why is it mentally so tough to push myself?

There is, alas, no simple answer to the million-dollar question. Experts confidently proclaim two basic things: The brain controls the amount of pain to which you willingly subject yourself, and the human body inherently does not like pain.

“Our brain discourages us from running to the point of disrupting the physiological homeostasis that our bodies depend on to preserve life,” says Fitzgerald, author of RUN: The Mind-Body Method of Running by Feel. “The brain won’t actually allow a true, 100 percent effort.” Robert Weinberg, a professor of sports psychology at Miami University in Ohio, adds that one’s goals may not be aligned with what one is truly willing to physically endure. “You may think you want a sub-three-hour marathon, but you may not be interested in doing the hard work it takes,” he says.

Running Rx: ”You have to train to suffer,” says Fitzgerald, adding that many runners embrace one type of suffering – usually the high-volume grind – but not the lung- and leg-burning type that creates speed. He recommends intervals, hill repetitions, and tempo runs at least once a week to build your mental muscle. “Discomfort should be an explicit objective of the workout,” he says. Realise you’re not up for that pain? Weinberg suggests pushing yourself more moderately by running with people who are slightly speedier than you are. The peer pressure will unconsciously make you mentally stronger – and faster.

16. Why do I get side stitches?

That pain that rips through your midsection, usually on the right side? Chalk it up to the act of breathing. Or, more accurately, to your diaphragm, the muscle that controls your breathing motion. “It attaches to the liver on the right side,” says Wyrick. “When you run, the attaching ligaments stretch, which stresses the diaphragm and causes pain.”

RELATED: 5 Ways To Help Ditch The Stitch

Running Rx: Slow down or walk so you can take deep, full breaths. Grabbing your right side and squeezing it to support the liver may also end the pain. Another option: When your left foot hits the ground, exhale, which causes your diaphragm to rise; inhale on your right foot, and it falls down, which decreases the stretching. Finally, keep training. Side stitches typically happen to beginners. “Over time, the ligaments become conditioned to the stress,” says Wyrick.

Jesse Lefkowitz

17. I use the bathroom right before I start, so why do I have to pee mid-run?

The urge to detour into the bushes can happen for a couple reasons, says Craig Comiter, associate professor of urology at Stanford Medical School: As your heart pumps blood more rapidly around your body, your kidneys may produce more urine, especially if you were well-hydrated prior to your run and you drink during it. You may also be dehydrated, and the concentrated urine in your bladder may give you that got to-go feeling; or, because of a slightly weak sphincter combined with the jostling of running, a bit of urine may leak through the bladder and stimulate the urethra, making you wish you could cross your legs while running. (Pregnancy causes the need for more pitstops, too.)

Running Rx: Take a pee break, says Comiter. If it happens a lot, schedule a pit stop at a urologist’s office.

18. Why does my nose run as fast as my feet?

Don’t chalk it up to empathy. A runny nose, a condition called exercise-induced rhinitis, is most likely because of the increased air flow; as your breathing rate increases, your nose kicks into hyperactivity. “Cool and dry air – or both – have been shown to increase secretions, similar to what we see in exercise-induced asthma,” says James Sublett, an allergist in Louisville, Kentucky. If you’re self-conscious about your drippy schnoz, know you’re not alone: A 2006 study, published in the Annals of Allergy, Asthma & Immunology, surveyed 164 exercisers and found that 40 percent had a runny nose while exercising inside, and 56 percent had one outside.

Running Rx: If your runny nose is a serious issue – it continues to run long after your workout and into your very important presentation – you might consider taking an antihistamine, or using an over-the-counter saline nasal spray prior to your run. Otherwise, stuff your pockets with tissues, and perfect your farmer’s blow.

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