Gabriella Boston / Special to The Washington Post

Muscle can turn into fat, lifting weights makes you look like Arnold and a thousand crunches a day will give you a six-pack. Yes, fitness myths are many, and they are persistent.

And they haven’t changed much over the years, according to Shirley Archer, a fitness and wellness educator with the American Council on Exercise.

“People are always engaging in wishful thinking that they can transform their body with minimal effort,” said Archer, who has written many books on health and fitness. “And our sound-bite culture isn’t helping. We stand in the grocery store line, and some headline tells us we can lose 10 pounds in 10 minutes.”

Let’s take a moment to clear up some of the most common fitness myths.

1. A higher number on the scale means you’re fatter.

It depends where those pounds are coming from: fat or muscle. “The difference is the density,” Archer said. A pound of muscle takes up less space than a pound of fat. That’s why it’s possible to become leaner and healthier while at the same time gaining weight. “So don’t be overly concerned with a specific number on the scale; it’s more about how you feel.”

2. Lifting weights makes women bulky.

Most women have nothing to worry about in terms of bulking up, says Victor Ibrahim, a team doctor for D.C. United. “First of all, it requires very intensive training that most people won’t do — like pyramid training.” Pyramid training is a system of overloading muscles, working them to exhaustion. Secondly, Ibrahim says, most women lack the testosterone levels to build bulging muscles. Weight training does create some muscle definition, which is something many women want. “Resistance training is actually essential for toning,” Ibrahim said.

3. When you stop weight training, muscles turn into fat.

“This is like saying that lead can turn into gold,” said Ed Ingebretsen, a American College of Sports Medicine-certified personal trainer. “Muscle and fat are two different types of tissue,” Ingebretsen said. When you stop training, you lose muscle mass, which in turn slows your metabolism, he says. The slower metabolism in turn can cause weight gain when you stop working out — but one type of tissue doesn’t “turn into” the other.

4. Running on a treadmill is better for joints than running outside.

Not so for most treadmills, Ibrahim says. “Unless it’s a high-quality, extra-shock- absorbing treadmill, it’s not going to make much of a difference,” he said. And the super shock-absorbing treadmills are not likely to be found in normal gyms, he adds.

5. Moderate aerobic work puts you in the ideal fat-burning zone.

“With any level of exercise you are using a mix of fuels,” Archer said. “Generally, the harder you work, the more fat you burn.” But before you can work at those most intense levels — i.e., anaerobically — you have to build up to it. “It’s progressive. You have to build some aerobic endurance before you can start working at high-intensity levels,” she said. In other words, walk before you run and run before you sprint — pushing the body progressively.

6. As long as you exercise you can eat anything you want.

“Individual metabolism determines how many calories we burn at rest and while we exercise,” Ingebretsen said. “If we eat more calories than we burn on a consistent basis, our bodies will accumulate these extra calories as fat regardless of the amount of exercise that we do,” he said. So, if you were thinking of adopting Michael Phelps’ 10,000-calorie-a-day-diet because you have started running a few miles a day, forget it.

7. Machines are safer than free weights.

Not necessarily. Machines are not designed for all body types. There are only so many ways you can adjust the seat and other settings. “Machines are kind of averaged out,” Ibrahim said. “They’re not going to fit everyone.” Free weights, on the other hand, can be adapted more easily. “But with free weights, it’s also easy to slip into bad habits,” he said. In other words, form, alignment and setup are important for both free weights and machines.

8. If you don’t sweat, you’re not working.

“Sweating is not always related to heart rate — which is the best measure of exercise capacity,” Ibrahim said. Sweat is just the body’s way to regulate body temperature, he says. And some of us just run hotter than others — sometimes independently of heart-rate levels.

9. Fat can be spot-reduced.

“This is just more wishful thinking,” Archer said. Fat reduction — in the midsection and elsewhere — will happen with a combination of healthy eating, cardio and strength work, she says. You don’t get to pick one body part or another. In other words, the 1,000 crunches won’t reveal the six-pack abs unless you also focus on healthy eating and some form of cardio- respiratory exertion.

10. Stretching before exercise improves performance.

The need for stretching is very individual, Ibrahim says, adding that many people, especially women, are hyperflexible and should consider focusing on building muscle to stabilize joints instead.

It’s best to stretch after working out, as muscles and connective tissue are warmed up and more receptive to “lengthening,” Archer says. She recommends slow and deliberate stretches and says to breathe deeply, hold a stretch for 10 to 15 seconds and repeat.