Quiz: Do you know the sweaty truth about these common fitness myths?

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May 18, 2022

Plenty of people are hitting the pavement, the pool or the trails this spring with new fitness goals but outdated information.

Exercise scientists have solved many mysteries in the past century or so, but it’s still easy to find old misconceptions stated as gospel and newer research presented as fact when the data behind it is much squishier.

See if you can pick out the truth — if there is any — in these common exercise science myths, starting with an easy one that might be the grandmother of them all.

Myth 1 of 8

If you swim too soon after eating, you’ll get a cramp and drown.

Not quite.

The Washington Post will not call Grandma a liar, so let’s just say she was misled. Snopes.com found this myth stated as fact as early as a 1908 British scouting manual, which called a post-meal cramp “very likely” and spiced the point with a little victim-shaming: “Cramp doubles you up in extreme pain so that you cannot move your arms or legs — and down you go. You may drown — and it will be your own fault.”

In Grandma’s defense, any type of strenuous exercise immediately after eating may upset your stomach. Jostling a full belly can make you feel bloated, sloshy and queasy, but it has not been shown to increase drownings.

People do sometimes get severe muscle cramps while swimming, as with any physical activity. And some swimmers drown. Most drownings occur in chilly water, when people can be jolted by physiological reactions known as a cold-shock response. Among the effects: involuntary gasping, which overrides the ability to hold breath. But the timing of a recent meal is unrelated.

Myth 2 of 8

Exercise alone is a great way to lose weight.

Not quite.

“You might lose some weight, but it won’t be the huge weight loss most people are seeking,” said Melinda M. Manore, professor emeritus at Oregon State University, who has spent her career studying nutrition and exercise science.

Our bodies evolved to hang onto stored energy, she said, so if we suddenly start burning more than usual, all kinds of complex internal regulators kick in to try to prevent big weight loss. Even people training for endurance events such as marathons rarely lose more than a few pounds, in part because hormones make them want to eat more to compensate. So losing weight and keeping it off typically require lifestyle changes and diet adjustments as well as physical activity, Manore said.

But if you blow off exercise because it doesn’t melt off pounds, you’ll miss all its other benefits.

Even a little bit of regular movement — such as walking your dog — can reduce risk of diseases such as diabetes, osteoporosis and some cancers, improve heart and brain function, and even make you look leaner as body composition changes.

“People don’t focus on all the wonderful things, outside of weight, that change,” Manore said. “The way they feel and move through space better, increased stamina to do the things they love to do without being out of breath, better sleep, more positive mental health — the list goes on and on.”

Myth 3 of 8

Smiling makes exercise easier.

Not quite.

This one may not be a myth, but we don’t know yet. The words “small study” are the big clue. But “smile!” appears anyway in many lists of trendy exercise tips, where a narrow but intriguing finding has been stripped of all nuance and condensed to bumper-sticker length.

The 2018 study, published in the journal Psychology of Sport and Exercise, indicated that smiling seemed to improve running economy by more than 2 percent. If that is true, it would be a significant gain, particularly for competitive athletes looking to hit time goals.

Researchers recruited 24 experienced recreational runners to run in six-minute chunks on a treadmill at a prescribed effort level while trying to maintain different facial expressions. Fourteen of the 24 runners ran more efficiently during the six minutes when they were trying to maintain a smile. Interestingly, 10 of the 13 men in the study ran more efficiently when they wore smiles.

When Hope College kinesiology professor Brian Rider saw the study, his scientific brain was skeptical, but his distance runner’s heart was intrigued.

“That’s such an easy, small little win you can get,” said Rider, who directs the college’s Health Dynamics program. “If something as simple as smiling can improve running economy, I’ll take it, and I know a lot of people would.”

So he set out to replicate the study, only he used 24 college soccer players. His findings, now undergoing peer review, showed no statistically significant link between smiling and performance.

Would it have worked if his soccer players were training for soccer instead of running on a treadmill? Why was there a gender difference in the first study? Whom might smiling work for, and why?

Rider said his work doesn’t disprove the original study but shows that more research is needed. He said smiling ends up on those lists of tips to try not because it’s a sure thing but because there’s really no downside. The only thing it could hurt is your game face.

Myth 4 of 8

The more you can drink during exercise, the better.

Not quite.

Some exercisers barely perspire; others leave puddles after a workout. So there is no one-size-fits-all rule for how much a person needs to drink to replace lost fluid, said Matthew Ganio, a professor of exercise science at the University of Arkansas who studies hydration.

Drinking too little leads to dehydration, which may hurt performance and can contribute to serious heat illness.

But drinking too much can also be dangerous. The excess fluid dilutes the blood, causing a sodium imbalance in cells that can lead to fatal brain swelling. The condition is called exercise-associated hyponatremia, and sports drinks do not contain enough sodium to prevent it in most people.

So how do you hit the hydration sweet spot? Ganio said the ideal answer is to figure out how much you sweat so you know how much fluid you have to replace. You can do that by weighing yourself before and after a workout, in several types of weather throughout the year. (The Korey Stringer Institute has detailed instructions.)

At the very least, Ganio said, “if you’re thirsty, you should absolutely drink.” Ganio said the body’s thirst mechanism isn’t perfect, especially during exercise, because it often doesn’t kick in until a person is mildly dehydrated. But being a little dehydrated is okay for most people in most situations, and drinking to thirst should keep them out of serious trouble.

Oh, and the eight glasses of water per day rule of thumb? Ganio said it is the most common hydration myth he hears, even though it was discredited long ago. It’s too darn easy to remember.

Myth 5 of 8

If you stop exercising, muscle will turn to fat.

Myth 6 of 8

Lactic acid causes sore muscles.

Not quite.

“I think there must be some place in the world, maybe many places, that churn out fliers saying that lactic acid causes muscle soreness,” said Gladden, who is also the president of the American College of Sports Medicine. Although the idea was debunked decades ago, he still hears it constantly.

The origin story of lactic acid as a muscle-trashing supervillain can be traced to the early 1900s, when researchers observed that muscles in frog legs fatigued as they filled with lactic acid. (To be clear, the legs were no longer attached to the frogs’ bodies but could still respond to electric stimuli.) The notion was subsequently supported by a Nobel Prize-winning scientist in the 1920s.

Conventional wisdom became that lactic acid was a waste product, that it caused muscles to tire during exercise, and that it caused soreness afterward.

But live human bodies work differently than the legs of dead frogs, Gladden said. Our muscles produce lactic acid in the form of lactate, which can be used as a muscle fuel.

Not only does lactic acid not cause next-day soreness — blame microscopic tears in muscles and connective tissue for that — but lactate is an important energy source for all kinds of tissue. As some hard-working muscles produce and release lactate, other muscles and tissues guzzle it up.

For instance, “if lactate levels are high and exercise intensity is high, the heart's primary fuel is lactate,” Gladden said.

Some lactate mysteries haven’t been unraveled. Gladden said he thinks lactic acid buildup may contribute to muscle fatigue and “burn” during hard exercise, but it is an open debate with respected researchers on both sides.

Myth 7 of 8

Sunscreen will prevent you from getting enough vitamin D.

Not quite.

This one’s not just for exercisers: Information about sunscreen applies to everyone.

Sunscreen helps prevent skin cancer and other skin damage; vitamin D strengthens bones and is thought to have many other health benefits. So you want enough of both. Fortunately, this is a have-your-cake-and-eat-it-too scenario.

The sun’s ultraviolet rays help convert vitamin D from the food we eat into a form our bodies can use, said Darrell S. Rigel, a clinical professor of dermatology at Mount Sinai Icahn School of Medicine.

Some lab tests indicated that sunscreen might hamper this process, but in real-life use, that’s not the case, Rigel said. He said sunscreen is tested at two milligrams per square centimeter, an amount much greater than anyone would actually apply. (“You’d be as white as that door behind you,” he said. For the record, the door behind me was very white.)

Your body can convert only a fixed amount of vitamin D a day, Rigel said. Once you reach that level, “it’s basically like the bucket’s full and it won’t convert any more that day until the bucket empties a little bit and there’s room for it.”

The average person’s bucket will be filled if they step outside for just five to 10 minutes a day, he said, even if only their face and hands are uncovered and even if they’re wearing a sunscreen with a high sun protection factor (SPF). If more skin is exposed, it takes even less time. So most people get plenty of sun in the course of a normal day.

But if his patients are worried about a lack of vitamin D, or if a blood test shows they are deficient, Rigel suggests keeping the sunscreen, SPF 50 or more, and taking a daily 1,000 IU dose of over-the-counter supplement vitamin D3 to top off the bucket. That type of vitamin D is pre-converted, he said — no sun needed.

Myth 8 of 8

Caffeinated drinks will dehydrate you.

Not quite.

Caffeine has long been known to improve exercise performance, but it supposedly came with a downside: The diuretic effect would contribute to dehydration.

Not so, according to a pile of research that shows caffeine not only doesn’t have a diuretic effect in athletes, but it also has very little in other healthy adults, especially if they’re accustomed to drinking it.

Just like other beverages, most caffeinated ones increase your body’s fluid balance rather than decrease it. (Note that we’re talking about typical caffeinated drinks — coffee, tea, soda, sports drinks — not energy drinks that contain widely varying amounts of caffeine and other stimulants.)

Ganio said a couple of cups of coffee might seem dehydrating because urinary flow will increase at first. But, he said, “your body is very smart in saying, ‘Well, we just went to the bathroom, so we’re going to hold on to more fluid the next time we get fluid.’ You always have the fluid in your body going up and down throughout the day.”

During exercise, over-peeing is not a problem because your body doesn’t produce much urine anyway. Blood is being sent to fuel working muscles and perhaps to cool your skin, and not much is going to your kidneys. So caffeine will have even less of a diuretic effect than it would if you were just, say, relaxing and taking an online newspaper quiz.