Business Insider asked three professional athletic trainers to debunk 17 of the most common exercise myths.

They explain that crunches don't give you abs, that women won't get bulky if they weight lift, and that cardio isn't the best way to lose weight.

Perhaps the biggest myth of all is that there's just one way to workout. Anything that gets you moving that you can also sustain over the long term, they said, will help you reach your fitness goals.

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Following is a transcript of the video.

Sean Kuechenmeister: One of the most common myths that I hear is that, if unused, muscle tissue converts into fat. It's really important to say that muscle tissue has muscle cells and fat tissue has fat cells. They are not interchangeable. By no means is it chemically or physically possible for muscle tissue to convert over to fat and vice versa, fat into muscle.

Narrator: That's —

Kuechenmeister: Sean Kuechenmeister. I'm a clinical athletic trainer at the New York Sports Science Lab in Staten Island, New York.

Narrator: And he's one of three athletic trainers we brought into our studios.

Janeil Mason: My name's Janeil Mason.

Andy Stern: My name is Andy Stern.

Narrator: To debunk 17 of the most common exercise myths.

Kuechenmeister: It really depends on your goals. Training fasted in the morning is more conducive to losing fat. Because when you wake up, you're in a fasted state.

Narrator: And that means ...

Kuechenmeister: Your body is basically consuming itself. So it's looking at fat storage. It's looking at muscle storage. That's the time where, if your goal is to lose weight and just slim down, lean down, that's the best time to optimize that window for training.

Narrator: But ...

Kuechenmeister: In terms of effectiveness of training in general, I don't think it really matters. You just need to make sure that, if you are training at night, you are not fatiguing yourself throughout the day.

So, when most people think stretching, they're thinking static stretching. You achieve a certain position, you hold that position, and your goal is to increase your range of motion. The problem with that is, you can end up really loose. And if you follow that type of stretching with something explosive or something ballistic or something strength-based, you now have a loose tissue, or you have a lax joint, and you're not gonna be able to produce as much force and you could also potentially lead yourself to being injured because you're not as stable.

Stern: So, one of my favorite is when it's the holidays, right, and you have that aunt or uncle that's just like, "Yeah, I'm just trying to lose it, like, right here," and they start pinching the lower abdomen. I'm like, "Oh, great, you can't spot-reduce the part that you want." And in good news, it doesn't go the other way either. It's not like, when I eat a cheeseburger, it's going to go right to my right hip.

Narrator: And if you are trying to lower your body fat, cardio isn't the best way to do it.

Kuechenmeister: Cardio doesn't burn fat; cardio burns calories. So if your goal is to lose weight, you want to be in a caloric deficit. So as a part of getting into that caloric deficit, doing cardiovascular exercises is helpful. But if you're not eating a diet or if you're not monitoring your caloric intake on top of that and making sure that you are in that deficit, no amount of cardio that you do, you can't outrun a bad diet.

Narrator: And, in fact, doing to much cardio can actually be a bad thing.

Kuechenmeister: If all you're doing is cardio with the goal of losing weight, you can start to burn into that muscle tissue. So if you're burning into your lean muscle tissue now, you could actually be slowing down your metabolism, you could be decreasing your bone density, and you could be making yourself weaker. Well, that's why I think this myth is potentially the most dangerous and damaging one for the general population.

Narrator: But it may not be as common as the belief that ...

Kuechenmeister: I love this one. One myth I hear all the time is that muscle weighs more than fat. A pound of bricks weighs the same as a pound of feathers. So it's not that muscle weighs more than fat; it's that muscle is more dense than fat. So in terms of you building muscle, you can add weight on the scale. The scale isn't necessarily the best indicator of progress when we're trying to develop our physique. And oftentimes, at first, you can add muscle and the scale will reflect that you're heavier. But over time, understanding that for all the lean muscle you have, you're increasing your resting calories burned per day. That's long-term sustainable change in your body as opposed to just doing cardio sessions and going into caloric deficit and starving yourself.

Narrator: Of course, building muscle isn't just for men.

Mason: Women think that they'll bulk up if they start working out. And if that's the look you're going for, I think that's great. 'Cause you're doing something that you want to do. But if you are working out for general wellness and health, I don't want you to be afraid to lift heavy weights. You're not going to get bulky, by nature.

Narrator: And, in fact, weight lifting is especially important for women.

Mason: As we age, we become more prone to getting osteoporosis. So we definitely need to be doing resistance training, where our muscles are feeling that stimulation so that the bones nearby can remain strong.

Narrator: And whether you're a man or a women, you don't actually need weights at all to build strength.

Stern: I mean, the myth being that you have to go to the gym to be doing strength training is crazy. All right? Your body is a weight. So, body-weight exercises have been around forever, and they're so important. To be able to push up your body, or crunch, or squat, or pull up.

Narrator: And if it's a six pack you're after, the muscles themselves aren't even that important.

Mason: Getting a six pack is not about doing tons of crunches. A lot of it has to do with your nutrition.

Narrator: And Stern agrees.

Stern: Abs are made in the kitchen. The abs are a muscle. If you're gonna target the muscle by doing crunches, leg lifts, bicycle crunches, oblique twists, you're essentially building the muscle. So think of it as, you're building the engine of the car, and then the outside is your body fat. And how do you show off the inside of the car? You've got to reduce that body fat.

Kuechenmeister: "Sweating a lot means you got a really great workout" is something I hear all the time. Unfortunately, that's not true, either. Some people are just naturally more prone to sweating. Some people just have underactive sweat glands. So it means that you're healthy in your filtration system, but it doesn't necessarily reflect the effectiveness of your workout.

Narrator: But if you do sweat a lot, how should you replenish?

Kuechenmeister: I would not say that most commercial sports drinks are the most efficient way of rehydrating following a workout.

Narrator: But plain water isn't going to cut it, either.

Kuechenmeister: If you are just consuming water, too, that's also not the most effective way of hydrating because hydration is not just water. There's also trace minerals that act as electrolytes, which help with nerve conduction, they help with brain function, they help with muscular contraction.

Narrator: So if you're looking for the best way to rehydrate post workout?

Kuechenmeister: It could be very beneficial to add just a dab of pink Himalayan sea salt to water. The pink Himalayan sea salt has over 60 trace minerals, all of which are found naturally in human sweat. So when you consider something like a Gatorade or a Powerade, they may have four or five different electrolytes in their blend. So they're falling drastically short in terms of overall hydration when it comes to all the minerals in your body.

Narrator: And after a workout, you should also eat protein immediately, right? If you already have a protein-rich diet, you don't need to worry so much about downing a protein shake right after your workout.

Kuechenmeister: Now, what you are gonna be depleted of, though, especially if you're doing anaerobic exercise, you're gonna be depleted of glycogen. Glycogen is the immediate form of energy for muscle contraction. And that comes in way of simple carbohydrates and sugars. So post training, it's important to replenish that glycogen.

Narrator: But even if you're fueling muscles with a proper diet, they still need time off.

Stern: Hashtag #NoDaysOff. The old myth that we should not take a day off is an extreme. There's a huge value in letting the muscle repair itself. Right? So every time you do, let's go back to the bicep curl, if I'm doing a bicep curl, a small tear is gonna happen in my bicep, so the body is going to repair itself. Because, again, it's a machine, and it knows how to survive. And if I continue to do it, I don't have a window of opportunity for the body, the soldiers to jump in and be like, "All right, let's fix this tear," because it's just constantly being worn. So it needs some of that downtime to heal itself.

Narrator: Especially if you're sore.

Kuechenmeister: That's a myth, for sure. Soreness is the breakdown of muscle tissue. It's the chemicals released during that breakdown. It's not an indicator of, "Oh, I'm getting stronger" or "Oh, I'm getting weaker." But if your soreness persists for longer than 72 hours, that could be a sign that you're underrecovering or overtraining. One month is not enough to undo a lifetime of bad habits. So, it's important to start slow, find the things that you enjoy, find the physical activities that make you feel good, make that a daily habit.

Narrator: And there's no one-size-fits-all approach.

Mason: There's not one type of movement that you should be doing that is better than the other. So if you enjoy dancing, go out and dance. Go out dancing three times a week or do a dance cardio class or something that gets you moving. If you like to jump on trampolines, do that. I think the best movement for anyone to do is something they enjoy. Because the only way that you're gonna stick to your workout being a lifestyle for you is for you to be doing something you enjoy.

EDITOR'S NOTE: This video was originally published in August 2019.