8 Fitness Myths That Drive Experts Crazy

When done right, exercise can be a veritable miracle drug. But follow the wrong advice and you can easily set yourself up for injury. Take the sit-up: Once considered the gold standard of core exercises, we now know that it can make low-back pain worse.

Fitness culture is rife with such misconceptions, thanks to constantly evolving science and fitness influencers who share tips based on “anecdote and gym lore,” said Brad Schoenfeld, a professor of exercise science at Lehman College in New York. “Once those opinions are disseminated to the public and take hold, they are hard to change.”

I asked more than a dozen fitness experts to share the myths they hear most often among their clients and patients, and that they wish they could debunk once and for all.

Myth 1: You should stretch before you work out.

If you’ve taken a high school gym class, you’ve probably been told to spend a few minutes stretching before exercising. But recent research has found that stretching before exercising is ineffective for preventing injury and may actually work against you. That’s because stretching a muscle for more than 90 seconds temporarily diminishes its strength.

“You’ve just transiently weakened all the muscle groups you’re trying to train,” said Dr. Josh Goldman, associate director of the Center for Sports Medicine at UCLA Health.

If you really enjoy the feeling of stretching before physical activity, don’t hold the stretch for long, Dr. Goldman said.

For the most effective preparation to work out, try a dynamic warm-up — a series of active exercises that get your blood flowing and gently stress your muscles. Save your stretching for a separate time, he said. “I like to tell people to do it before bed,” since it gives your muscles time to recover before moving again.

Myth 2: You need to lift heavy weights to build muscle.

Not true, said Dr. Schoenfeld, who studies muscle growth. A significant body of research now shows that lifting relatively light weights for, say, 30 repetitions is just as effective at building muscle and strength as lifting weights that feel heavier for five to 12 reps. It’s a matter of personal preference.

But don’t avoid heavy weights for fear that they will make you “bulk up,” said Dr. Jacob Sellon, a sports medicine physician at the Mayo Clinic. “It actually takes a lot of effort” to build Popeye muscles, he said. “It doesn’t just happen with typical strength training.”

Myth 3: Running destroys your knees.

Fear not, research has debunked the notion that running increases your risk of osteoarthritis, and even suggests it can protect your knees against the condition. In fact, not moving increases your risk of developing osteoarthritis, along with age, weight and genetics.

For years, experts thought that “our knees were like tires — you drive the car a lot, you burn through your tire tread,” Dr. Goldman said. “That is not true, because our body is dynamic,” and our joints can regenerate themselves, especially when we are regularly active.

That said, running can definitely lead to knee pain or injury if you train too aggressively, said Dr. Jordan Metzl, a sports medicine physician at the Hospital for Special Surgery in New York. Dr. Metzl called this “violating the rule of toos” — running too fast or too far too soon. “Increase slowly,” he said. And if you start to feel knee pain, get it checked out as soon as possible by a sports medicine expert.

Myth 4: Walking is enough to keep you fit as you age.

Walking is popular among older Americans for good reason: It’s been shown to lower the risk of heart disease, diabetes and certain cancers, as well as the risk of premature death. And it’s so doable.

But walking on its own is not enough to stay fit as you get older, said Anne Brady, an associate professor of exercise science at the University of North Carolina-Greensboro. Starting in your 30s, your muscle mass progressively declines, she said, so you also need to focus on strength training.

“People can do daily activities with a minimal amount of cardiovascular fitness,” she said. “But when they don’t have the strength or the muscle power to do daily activities, that’s when they lose their independence.”

Complement walks with at least two 20-minute strength-training sessions every week.

Myth 5: Modifications are for beginners.

Choosing to do a less-strenuous version of an exercise — say, a push-up or plank with your knees on the ground — doesn’t mean you’re weak or a novice or that you’re backsliding, said Stephanie Roth-Goldberg, a clinical social worker and therapist in New York who works with athletes. It’s a sign that you’re listening to your body and keeping it safe.

“Our bodies require different things on different days,” she said. “Modifying exercises helps us work on form and the mind-body connection.”

Myth 6: Runners and cyclists don’t need to strength-train their lower body.

Amanda Katz, a certified strength and running coach in New York City, said she often has to convince clients who run or cycle that they also needed to strength-train their lower body.

Pounding the pavement or pushing pedals does strengthen your lower body, but not enough to stimulate significant muscle growth, she said. A strength-training regimen that includes squats, lunges, glute bridges and pointers can improve bone density and lower your risk of injury — and make you a stronger runner or cyclist, too.

Myth 7: You need 10,000 steps a day to be healthy.

Nope. Exercise scientists debunked this one years ago, but many Americans still see it as a benchmark of good health, said Cedric Bryant, the president and chief science officer of the American Council on Exercise

The myth traces back to the 1960s, when a Japanese clock manufacturer mass-produced a pedometer with a name that translated to “10,000-steps meter.” “Unfortunately, it’s taken on a life of its own, because the research clearly doesn’t support there being anything magical about that goal,” Dr. Bryant said.

The latest research suggests that the health benefits of walking appear to plateau at around 7,500 steps, but even as few as 4,000 steps per day can reduce the risk of dying from any cause.

Myth 8: Taking an ice bath after a tough workout improves recovery.

Plunging into an icy tub after a difficult workout can feel like a safeguard against injury, since it helps to reduce inflammation. But there’s a problem with this.

“Not all inflammation is bad inflammation,” Dr. Goldman said. If you jump into an ice tub after every workout, you slow or stop the repair process.

When you work out, you create useful inflammation by strategically stressing your muscles, and as the body heals, it builds strength, he said. If you want to tend to a specific injury after a workout, Dr. Goldman recommended either icing the injury itself or waiting a day before taking a cold dip, to give your muscles time to start the repair process.

The same rule applies to over-the-counter pain medications like NSAIDs: Because they’re anti-inflammatory, you should only take them after a workout if you’re treating an injury. Otherwise, you risk counteracting your training.

“Cold water immersion is a very good anti-inflammatory tool, but you’ve got to use it in a time where you actually want to prevent inflammation and not as a prescription after every workout,” Dr. Goldman said.

For overall recovery after a workout, research suggests saunas may be safer and more effective.