Exercise is a critical part of a healthy lifestyle, but health clubs and gyms are also home to a bulked-up trove of myths.
Fortunately, ABC News OnCall+ Wellness has called on its experts to explode some of the perennial misinformation we've all heard about exercise.
"It's important to remember, in some of these myths, that it's different for a person who's been injured as opposed to someone who's healthy and not injured," said Dr. Sherwin Ho, an orthopedic surgeon and director of the sports medicine fellowship at the University of Chicago Medical Center.
"[For] those that are injured, some of these myths are actually true, and that's where they came from."
While everyone receives different exercise advice, it's clear that everyone can benefit from the exercise itself.
Learn more about Dr. Richard Besser's "Doc at Your Gym" trainer Kira Stokes
"I'm a person who believes in health at every size," said Joanne Ikeda, a nutrition education specialist at the University of California at Berkeley.
She said that even in larger people, working out can reduce the risk of chronic diseases and make them more manageable.
Further, she said, weighing more does not, by itself, mean that someone is less healthy.
"I think what's important are the metabolic indicators of fitness," Ikeda said, noting that doctors look at things like blood pressure, cholesterol level and circulation when evaluating patient health.
Doctors should be consulted whenever you start a new workout regimen, but we hope these tips from our experts will help you ask better questions and give your doctor more helpful information.
Fact or Myth? Crunches Will Flatten Your Stomach
Crunches alone won't flatten your stomach, because there are no exercises to reduce fat in specific areas of your body.
"Basically, you can't spot reduce. Your body decides where to store fat, and a lot of that is based on your genetics," said Gerald Endress, fitness manager for the Duke Diet and Fitness Center.
The best way to get a flat stomach is to burn calories to reduce fat in the first place. Crunches will tone areas, but won't reduce the fat there on their own.
Exercise in general will burn calories and reduce body fat overall, said Ho.
"If the majority of your fat is in your abdominal or stomach area, yeah, you'll notice a difference, but it will burn it everywhere," he said.
The myth of crunches flattening your stomach may have evolved because sometimes crunches give the appearance of reducing stomach fat.
Ho noted that crunches burn calories, so performing large numbers of them every day will contribute to weight loss but not as effectively as cardio.
Endress said that crunches might also seem to have a stomach-flattening effect because they can tighten and strengthen the muscles that support the back, creating the appearance of a flatter stomach.
Endress said that an exercise routine to flatten the stomach might vary by person. "You basically want to pick an activity you can stay with consistently during the week."
He said he often recommended strengthening the area through Pilates, yoga and muscle training that focuses on the torso.
Fact or Myth? If You Stop Working Out, Your Muscle Turns to Fat
Muscle turns into fat only in very rare circumstances, and it never occurs in healthy people.
"They're two different types of cells," said Endress. "Muscle doesn't turn into fat, and fat doesn't turn into muscle."
This myth probably originated from people seeing toned, muscular athletes develop some extra layers of padding with age.
What actually happens, Endress said, is that when you stop working out, you rapidly lose muscle and gain fat, potentially giving the appearance that muscle is turning into fat.
"It's almost like a slang colloquialism that people use," he said.
Also, once people stop working out, they usually don't cut back on the calories they were consuming before but are no longer burning off.
Ho said that muscle can literally turn into fat, but "You only see it in those extreme circumstances."
"If you're talking about healthy muscles that aren't torn or injured, then no. For a noninjured muscle, that's a myth. But it's true with serious injury, like with a complete rotator cuff tear being the best example."
The difference, Ho explained, is that with a complete tear, the muscle isn't just infrequently used, it isn't used at all, and it can be replaced by fatty tissue. But he noted that even then, it is unusual.
Fact or Myth? Eating Protein After a Workout Will Build Muscle
"That's definitely a myth," said Elisabetta Politi, a nutrition director at the Duke University Diet and Fitness Center. "What you need after a workout are carbohydrates."
When you work out, your body uses the glycogen stored in your muscles and liver. Glycogen is made from carbohydrates like glucose.
The exhaustion you feel after a workout, Politi said, comes from a lack of glycogen.
"The best way to be re-energized is to eat carbohydrates," she said.
Protein is helpful in toning existing muscle. However, Politi said, the average American eats twice the necessary amount of protein already.
"If [you're] eating an average diet, [you're] probably getting plenty of protein," she said.
Fact or Myth? You Need to Stretch Before Exercising or You'll Injure Yourself
Answer: Probably a Myth
Had this article been written a few years ago, this might have ended up in the "Fact" column.
"We go back and forth on that," said Ho.
The most recent studies, he said, have found that stretching will not help you avoid injury.
"I think in people who have been injured or are injury-prone, those people would benefit from stretching," said Ho.
He said people who, for instance, have torn their calf muscle, should stretch both calves before exercising, but they should jog a little first.
"I think the key, what we do recommend, is that you warm up before stretching," said Ho.
Endress said that with his clients, he recommends some sort of slower-paced warm-up.
"Whatever activity you're doing, start off at a slower pace and gradually build up."
He suggested warming up for three to five minutes before starting, which would include aerobic exercise before weight training.
Stretching is also helpful after a workout, where it helps to maintain flexibility, which can be particularly important after weight training.
But alone, before exercise, it isn't warranted.
"Stretching in and of itself, for someone who has normal flexibility, has not been injured, may not reduce injury," said Ho, but he said that more research was needed before drawing a definite conclusion.
Fact or Myth? Running Destroys Your Joints
Answer: It Depends
Whether or not running will damage your joints likely depends on your injury history, so it is a good idea to see your doctor before starting a running regimen.
"If you already have an injury, for example, your knee, then running or any other repetitive high impact activity can do further damage to your knee," said Ho.
Endress said that while running might benefit people without an injury history, there are a few things they should keep in mind, such as the need to replace their shoes frequently, and the benefits of nonconcrete surfaces.
He noted that the impact of running on pavement can be problematic, particularly for people who are obese, and said it's probably worthwhile to find softer ground, such as grass, to run on.
However, for healthy people, running should not do any damage.
"If we take a healthy knee and we use proper running habits or running techniques, in a healthy, injury-free person, you can run without causing damage to your joints," said Ho.
Fact or Myth? Exercising Once a Week Isn't Worth It
"Any exercise is better than no exercise," said Ho. "Any exercise, even once a week, will benefit the patient because they will burn off the calories they would not have otherwise burned off."
He said, however, that it won't help people reach their weight loss goals.
"If you're looking specifically, with a goal in mind, to lose weight or to train for an event, for instance training for a marathon or trying to get back into shape, once a week would not be frequent enough to make progress, to reach a specific goal," said Ho.
Endress cautions that once-a-week exercisers, whom he called binge exercisers, are more prone to injury, because they are not used to the strain.
However, he said, one day a week of exercise can still help one get into or maintain a healthy routine.
"For some people, if that's all you can do at this point, that is a good way to at least be consistent with exercise," he said.
Later on, other days of exercise could be added. Also, he said, one day a week might be all someone can manage during the holiday or tax season, but it would make it easier to resume a normal exercise schedule once that period has ended.
"If you can only get in one day, that's at least going to continue the behavior until you can expand out to more days during the week," said Endress.
Fact or Myth? Weight Gain Is Inevitable With Age
Weight gain is not inevitable with age, but is likely because metabolism slows down, and many do not cut their intake of calories.
"If we eat in our 60s the way we were eating in our 20s, of course we're going to gain weight," said Politi.
In addition, most people became less active with age.
"Most people gain weight because they are becoming more sedentary and they keep eating the same as they were when they were young," she said.
The decrease in metabolism is very gradual, however, so Politi notes that being a little more active each year should counter that.
"There's really no reason why you should gain weight as you age, if you become more vigilant."
But simply gaining weight is not a tell-all for poor health, said Ikeda.
"I think it's a myth that you should weigh what you weighted at 21 for the rest of your life," she said. "A 60-year-old does not have the same potential for fitness a 20-year-old has."
She said more research is needed in this area to determine when weight gain becomes a problem, because people will typically gain weight as they get older.
"We don't know how much weight people should gain over a lifetime once they're an adult," said Ikeda.
Fact or Myth? If Your Parents Are Overweight, You Will Be Too
Answer: Myth -- With a Healthy Dose of Truth
"That has been shown to hold some truth," said Politi.
Weight as an adult has been shown to have a strong genetic component, although the lifestyle habits you are brought up with also play a role.
"It's probably what your parents feed you and the level of activity you do as a family," she said. "There's definitely a genetic contribution, but it's not the only one."
Politi said that while human genes have not changed drastically in recent years, there is an epidemic of obesity because we are more sedentary and eating more calories.
"If you're vigilant with your food choices and you exercise, I don't think you're going to gain weight, or at least you're not going to gain as much weight as someone who is not careful."
By working out properly, weight can be held in check. "Nothing is preordained," said Ikeda.
However, she noted, weight alone does not determine your health.
"Certainly your risk or chances of being overweight are greatly increased if your parents are overweight, and there are plenty of studies to back that up," she said.
However, Ikeda said, "If you have large parents, your chances of being big are increased, but that doesn't mean you can't live a happy healthy life."
By exercising, she said, you can live healthily even if you carry more weight than others.
Fact or Myth? Physically Fit=Healthy
"They're closely linked, but they're not the same thing," said Ikeda.
She noted people who are not considered "healthy" can live well through exercise, and exercise can help them manage chronic diseases they may have.
For example, Ikeda said, people with type 1 diabetes or people who have recently suffered heart attacks or strokes can better manage their illnesses if they are in good shape.
"It certainly helps in terms of handling any kind of disease or illness that you have," she said.
Politi noted that many people stay thin in their 20s and 30s without exercising, but beyond that most need a workout regimen, unless they are "blessed by great genes."
Even then, she said, thin people can benefit from exercise, which combats physical conditions as well as mental conditions, like depression.
"Studies have shown that exercise helps reduce the risk of heart disease, helps resist the risk of cancer."
Fact or Myth? Women Who Weight Train Bulk Up
"For a woman to bulk up, it takes a tremendous amount of weight training, more so than men," said Ho.
Men who work out a lot may bulk up, but that is because of the anabolic testosterone that men's bodies produce. The average woman, therefore, should not be worried.
Ho said that women who do strength training may gain some mass, but "they will lose an equivalent amount of mass, or bulk if you will, in fat."
Effectively, he said, they are "trading fat for muscle. That extra muscle mass will help them burn the extra fat."
Some women do bulk up after weight training, Ho said, but they have often done something to alter their body chemistry.
Endress noted that women typically use lighter weights when doing strength training, and that alone will not lead to bulking up.
For women, he said, he encouraged different types of strength training, such as Pilates, which focus on the core of the body.
However, he said, it's not for concerns about getting larger.
"It's very difficult to bulk up, so you won't see that from doing general strength training. For everybody, it's not easy to gain muscle mass -- that's a myth in itself."
Visit the ABCNews.com OnCall+ Wellness Center to get more tips on keeping your health on track.