Is your exercise routine designed to target fat in your belly, arms, or elsewhere? Are you a woman who’s avoiding lifting weights out of fear you’ll look too “bulky”? Are you not running because it may wear out your knees? Are you skipping cardio because you’re worried that it will kill your strength gains? We’re here to set the record straight. 

Myth #1: Exercise before breakfast to burn more body fat 

To maximize fat burned during exercise, roll out of bed, lace up your sneakers, bypass the kitchen on your way out the door, and get your heart pumping. Or so the theory goes.  

“The claim has a logical basis,” explains Brad Schoenfeld, professor of exercise science at Lehman College in New York City. “If you don’t consume food prior to exercise, your glycogen—which is carbohydrate stored in the muscle and liver—will be somewhat depleted. So your body would rely more on fat than carbohydrate for fuel during exercise.”  

And people do burn a bit more fat during exercise that’s completed before they’ve eaten than when they exercise after eating. 

The problem: “The theory is shortsighted,” says Schoenfeld. “It only considers what happens during the exercise session. But how much fat you’re burning in this minute or the next doesn’t matter. Body fat loss happens when you’re burning more calories than you’re eating over the course of weeks.” 

Only a handful of small studies have tested whether exercising before or after eating causes greater fat loss over the course of weeks. “They show no meaningful difference,” says Schoenfeld. 

For example, Schoenfeld randomly assigned 20 young women to eat a lower-calorie diet and drink a 250-calorie shake either before or after running on a treadmill for an hour three times a week. After four weeks, the two groups had lost the same amount of body fat. 

Bottom line 

“If you want to eat before you exercise, eat before,” says Schoenfeld. “If you don’t want to, don’t. It’s not going to make an appreciable difference to fat loss one way or the other.”  

Myth #2: No pain, no gain 

Using soreness after you exercise to gauge how good your workout was? You need a new yardstick. 

For many people, the calculus goes like this: A challenging workout results in micro tears in the muscle fibers, and that kind of “good” muscle damage—it leads to muscle repair and muscle growth—causes soreness. So if you feel sore, that surely means you’ve got bigger, stronger muscles coming your way. And if you feel nothing the next day, did you even work out? 

But there are some flaws in that logic. 

For starters, “We’re still not completely sure what causes soreness at the level of the muscle,” says Schoenfeld. “It’s related to muscle damage, but whether it’s damage to the muscle fibers themselves or to the connective tissue like the fascia or a combination is not completely clear.” 

And soreness likely isn’t even a good gauge for muscle damage (let alone muscle growth). 

One of the best markers of muscle damage is a drop in the amount of force that a muscle can produce. But in a study in 110 young men who performed a challenging biceps workout, soreness wasn’t related to muscle force or other markers of muscle damage like inflammation. 

Schoenfeld looks at the causes and consequences of soreness differently. 

“Novelty causes soreness,” he explains. When you start training your muscles for the first time after taking a long break, or if you’re trying something new, the odds are higher that you’ll get sore. Over time, you’ll get less sore even if you’re gradually increasing weight or intensity. 

“Let’s say you do a novel exercise,” says Schoenfeld. “Your body isn’t used to that exercise, so there’s going to be muscle damage, which can be quite severe if you overdo it. However, if you do that exercise again relatively soon, usually within several days to a week, your body will have experienced that movement before and you’ll have much less damage. And after a few weeks, the connective tissue has gotten stronger and the body does a better job at activating more muscle fibers and distributing the workload across the fibers. So the muscle has adjusted its response to the exercise, and it’s able to stave off the damage.” 

During that time, you’ll be slowly building larger, stronger muscles. No soreness required.  

But you don’t need to avoid soreness altogether. “You want to avoid severe soreness,” says Schoenfeld. “People who chase soreness and end up walking like Frankenstein the day or two after a hard workout won’t be able to train effectively for days on end after. And that’s going to have a negative effect on your ability to build muscle or strength.”  

Schoenfeld’s advice: “When you’re just starting out with strength training, err on the side of caution and be judicious about how much and how hard you’re working out.” Then, over the course of a few weeks, you can start increasing the weight or the intensity of your workouts.  

Bottom line 

Don't shoot for soreness. More isn't better, and it can make it harder to stick with your strength-training program. 

Myth #3: Enhance your workouts with an ice bath 

Cold water plunges are all the rage. They’re popular among everyone from Harry Styles to Joe Rogan (and, probably, your neighbor). Proponents claim that submerging yourself in cold water after a challenging workout can reduce swelling and inflammation and hasten recovery so you can emerge stronger and less sore. Is that true? 

“The literature pretty consistently shows that cold water immersion can accelerate recovery from soreness,” says Susan Kwiecien, manager of clinical research at the Nicholas Institute of Sports Medicine and Athletic Trauma at the Manhattan Eye, Ear & Throat Hospital at Northwell Health. “It works very well for reducing pain and soreness.” 

That’s the upside. The downside: “Ice baths blunt muscle development following resistance exercise,” says Kwiecien. Several studies have shown that hopping in an ice bath after you’ve racked your weights blunts the signaling processes that lead to muscle growth and may negate much of the hard work you’ve done in the gym. While that wasn’t seen in all studies, there’s no evidence that ice baths help muscle growth or strength. 

In one of the longest and best studies, researchers randomly assigned volunteers to sit in a 50º F cold water bath or to ride a stationary bike at a light, easy pace for 10 minutes after each session of a lower-body strength-training program. After 12 weeks, strength and muscle mass increased more in those who pedaled than in those who plunged (the pedaling wasn’t intense enough to build muscle). For example, quadriceps muscles grew by about 300 grams in the biking group compared to just 100 grams in the cold-water-immersion group. 

That said, most studies have been small and were carried out in young men. How ice baths affect muscle growth in women, older adults, and people of varying levels of fitness remains to be seen. 

In some situations—if you’re seeking a quick recovery, say—an ice bath might be a good idea. “It can be great for weekend warriors,” says Kwiecien. For example, if you play on a soccer team that has games two days in a row, “an ice bath will help you be less sore so that you can play the next day.” Ditto for a weekend of skiing, so that you can hit the slopes on Day 2 without having to stick to the bunny hill because your quads are too sore. 

If you try it, don’t use really cold water, says Kwiecien. “If you start shivering, that’s your body’s alarm bell that your core temperature has dropped too much.” Instead, opt for slightly warmer water that you can stay in for longer.  

“The literature has shown that duration matters more than temperature because duration is related to the magnitude of change in muscle tissue temperature,” notes Kwiecien. That’s because it takes time for the cold to permeate down to your deepest tissues. If you’re in and out within a couple of minutes, you’ve made your skin frigid without affecting your muscles. 

Kwiecien suggests soaking in 50º-to-60º F water for 10 to 15 minutes. “But tailor that based on how you’re feeling,” she adds. “And remember, your body fat is an insulator. So people with more body fat will cool more slowly.” 

Bottom line 

If you’re trying to build muscle, skip the cold plunge after your workout. If you want to occasionally prevent soreness, stick with cool water that you can tolerate for at least 10 to 15 minutes.  

Myth #4: You can “spot reduce” fat 

We’ve all seen the claims: “Lose belly fat in 10 days!” “5 effective exercises to reduce arm fat!” But don’t be fooled. Strengthening the muscles in your abdomen, arms, or anywhere else doesn’t mean you’ll burn more fat from that area. 

“The idea is that the generation of heat from working the muscle will liberate fat from the fat cells that surround that muscle,” explains Schoenfeld. Nice idea. Too bad there’s nothing to it. 

Doing crunches to try to burn belly fat? “Your body is no more likely to burn fat from your abdomen than from fat cells elsewhere,” says Schoenfeld. 

Research shows that targeted exercises—like crunches for your abs or triceps dips and biceps curls for your arms—don’t lead to localized fat loss. In one study, researchers had 104 adults perform strength-training exercises on only their non-dominant arm twice each week. After 12 weeks, the trained arm had no less fat than the untrained arm. 

In another study, 30 women with excess weight were randomly assigned to eat a reduced-calorie diet or to follow the diet in addition to doing a series of ab exercises like crunches, oblique crunches, and abdominal bracing three times a week. After 12 weeks, both groups had lost similar amounts of weight and fat, with no differences in waist size or the amount of fat in their abdomen. 

What governs where you lose fat? “Mostly genetics,” says Schoenfeld. “People have different propensities to lose fat from different areas.” Some people will lose it from their thighs first, others from their belly, hips, arms, or face. “You can’t dictate where your body is going to pull fat from.” 

Bottom Line 

Don’t expect crunches to blast away belly fat. Where you lose fat from is largely determined by your genes, not by which muscles you strengthen.  

Myth #5: Lifting weights will make women bulk up 

Ladies, if you’ve been steering clear of the weight rack at the gym to avoid getting too “bulky,” let us quell your concerns.  

“Women’s ability to gain appreciable muscle is somewhat limited,” says Schoenfeld. And while a number of sex-based differences can explain that, one stands out: “Women don’t have much testosterone, which is a key hormone for muscle growth.” 

In fact, most people—not just women—struggle to put on large amounts of muscle. Building significant muscle mass requires dedication to a program of strength training that continuously challenges your muscles. You’re not going to end up with chiseled shoulders and powerful thighs without working at it. 

“If it were that easy to gain muscle, we’d have a lot of people who look like bodybuilders walking around,” says Schoenfeld. “Go into any gym and most people do not look very big. And many of them have probably been training for years.”  

If, by some stroke of luck, you’re one of those people who put on muscle easily and you decide you don’t like the look of it, “it’s very easy to lose muscle,” Schoenfeld points out. That’s because muscles operate on a use-it-or-lose-it basis. “It’s not like you’re stuck with it. I wish that were the case.” 

But you’d be smart to try to keep any muscle you build. “Gaining muscle has a huge number of benefits,” says Schoenfeld. More muscle means a lower risk of falls and higher odds of remaining self-sufficient as you age, better blood sugar control, and maybe even living longer. 

And weightlifting isn’t the only way to build muscle. Maybe bodyweight or resistance-band exercises, Pilates or barre, or boot camp classes would suit you better.  

Just don’t believe any marketing that promises “long, lean muscles” from one type of exercise over another. “The shape of muscle is genetically predetermined,” says Schoenfeld. What a muscle looks like depends on the length of the muscle belly (the thickest part of the muscle) and where the muscle attaches to the bone via the tendon. “Some people have long tendons. Some people have short tendons.” Assuming two people have thigh bones that are the same length, the person with shorter tendons will have longer muscles. And you can’t change that through training. So choose a type of strength training based on what you enjoy, not based on promises of how it will make you look. 

Bottom line 

It takes a lot of consistent, hard work to put on a noticeable amount of muscle. You won’t get “bulky” by accident, and the benefits of strength training are too important to forgo. 

Myth #6: Running will wear out your knees 

If you’re a runner, you’ve likely heard the well-meaning warning that your beloved habit is eventually going to do a number on your knees. Or maybe you’re avoiding running now, assuming you’re doing your future knees a favor.  

Those concerns aren’t entirely unfounded. “The knee is the most frequently injured body part in runners,” acknowledges Jean-Francois Esculier, head of research and development at The Running Clinic and clinical associate professor in the department of physical therapy at the University of British Columbia. 

But those acute injuries don’t necessarily mean that running is bad for most knees over the course of a knee’s life. On the contrary, “the latest research shows that runners have three times less knee and hip osteoarthritis than sedentary non-runners,” says Esculier. (Of course, something other than running—a history of injury or genetics, for example—might explain the differences between sedentary people and runners.) 

“The exception to this may be elite runners, who have a higher risk of knee and hip arthritis than recreational runners and sedentary people,” adds Esculier. (He’s talking Olympic-level and professional athletes.) “But for 99 percent of runners out there—even those who aim to qualify for the Boston Marathon—running is likely beneficial to their knees.”

Already have arthritis in your knees but still love to run? Though research is limited, it indicates that you don’t need to stop. “There is no evidence to suggest that osteoarthritis would progress any differently in people who continue to run,” says Esculier. That is, cartilage isn’t likely to degrade more, nor will the space in the joint shrink any faster.  

In fact, “based on early evidence from studies that follow people with knee osteoarthritis over time, those who run may end up decreasing their pain levels more than those who don’t run.” 

One reason for misconceptions about running and knees may be rooted in past beliefs about cartilage. “We used to think that cartilage couldn’t get stronger because it lacked a blood and nerve supply,” explains Esculier. “We thought it could only wear out.” 

“But now we know that running stimulates fluid moving out of the cartilage during the run and then back into the cartilage when the run is over. This process brings nutrients to the cartilage, which helps it adapt and get stronger with activity, much like your muscles and bones get stronger with exercise.” 

Like all types of exercise, introduce running gradually. “Avoid drastic increases in distance or speed,” advises Esculier. “Listen to your body. Don’t run through pain unless it was advised by a qualified healthcare professional.” 

Bottom line 

“We need to forget the old idea that running is bad for the knees,” says Esculier. “Running is good for the knees. Too many people receive bad advice to quit running because their knees hurt. If someone has pain while running, they can take a break for a few days or weeks, but the majority will be able to go back to running and ramp things up gradually. Rare are the people who should avoid running altogether.” 

Myth #7: Cardio is killing your muscle gains 

Are you taking a “None for me, thanks” approach to cardio—or aerobic—exercise because you’re worried that it may prevent your muscles’ size and strength from realizing their full potential? 

“There is evidence that cardiovascular exercise upregulates an enzyme that inhibits muscle-building enzymes,” explains Schoenfeld. “So the theory is that you shouldn’t do any cardio so that you can optimize muscle growth. But that’s overly simplistic.” 

Rather, “within wide limits, there’s no good evidence that doing aerobic exercise will have negative effects on strength gains,” he adds. In one review of 43 trials, researchers examined the effects of strength training with or without aerobic exercise on muscle size, muscle strength, and explosive power. (That’s the ability to apply strength over a short period of time, which is essential in some weightlifting moves like a clean and jerk or a snatch. And in older adults, it’s important for preventing falls.)  

The results: Aerobic exercise didn’t interfere with building muscle size or strength. That was true whether people cycled or ran or whether they did weightlifting and aerobic exercise in the same session, on the same day, or on different days. 

But the review did have a few cautions. “There are some caveats if you’re a powerlifter or a bodybuilder,” says Schoenfeld. The combination of aerobic exercise and weightlifting blunted explosive strength, especially if both were completed in the same workout. “That doesn’t mean power lifters should do no aerobic exercise,” Schoenfeld adds. “It’s good for cardiovascular health and helps improve circulation, which is important for recovery.”  

Another caveat: “If you take it to the other extreme, marathon training, you’re definitely going to see negative effects on your muscle-building capacity,” says Schoenfeld. “Number one, you’re draining energy resources. Number two, you’re going to risk overtraining if you do a lot of strength training along with high amounts of aerobic exercise.” 

For almost everyone else who exercises between the extremes of body building and marathon training, “moderate amounts of cardiovascular exercise will not negatively impact your strength or muscle gains,” says Schoenfeld. Daily brisk walking, jogging a few times a week, or even a few rounds of high-intensity interval training each week are all a safe bet for people who also want to build muscle. 

If you’re still concerned or you’re focusing on power lifting, “separate your bouts,” Schoenfeld recommends. That means doing cardio training on days when you’re not strength training. Or doing a morning session of one and an afternoon session of the other.  

Only have time to do both in one session at the gym? “If your goal is muscle building and strength, I would not recommend doing aerobic exercise before strength training,” says Schoenfeld. “That can tire you out so you’re not able to push your muscles as hard.” 

But if your goal is to build your cardiovascular fitness, the sequence of events likely doesn’t matter. “If you do strength training before aerobic exercise, you’re not going to negatively affect your aerobic training.” 

Bottom line 

Don’t skimp on cardio workouts just because you’re trying to build muscle. Cardio won’t diminish your muscle gains, and your heart will thank you.