NEW YORK (Reuters) - Can crunches create six-pack abdominal muscles? Do weight-lifting women risk bulging biceps? Is stretching always a good idea?

Experts say disentangling folklore from fact is not easy in fitness, where misconceptions are as pervasive as push-ups and as stubborn as love handles.

Jennifer Burke, a fitness manager at a Crunch gym in West Hollywood, California, said many women still worry that weight training will create big and bulky muscles.

"Women say ‘I don't want to get bulky,' but unless you take in extra calories or testosterone supplements, that's just not going to happen," said Burke, who eases reluctant clients into resistance training gently, with body-weight exercises.

"When they see their bodies getting long lean muscles, getting toned, they trust you a little more and you can start adding in dumbbells and machines," Burke said.

The U.S. Centers for Disease Control and Prevention (CDC) recommends that adults engage in muscle-strengthening activities that work all major muscle groups - legs, hips, back, abdomen, chest, shoulders and arms - two or more days a week.

"A lot of people think if they want to lose a lot of weight they should do cardio, but the best thing is to add in resistance training as well," Burke said. "You'll get bigger, faster results because you're working on lean muscle tissue which burns more calories in the long run."

While it's true that muscle weighs more than fat, it's also more compact.

"Five pounds (2.3 kilograms) of muscle is the size of your fist. Five pounds of fat is the size of your forearm" she said.

Burke added that another misconception is that lower-intensity exercise such as the fat-burning setting on most cardio machines is better for burning calories.

"That's absolutely not true," said Burke. "If you increase the intensity you'll burn more calories."

The CDC's rule of thumb is that one minute of vigorous-intensity activity is about the same as two minutes of moderate-intensity activity.

TOO MUCH OR NOT ENOUGH

Stephanie Huckabee, a South Carolina-based fitness instructor, said people who believe it is necessary to exercise every day are setting themselves up for failure.

"I tell my clients to expect days when they don't exercise," said Huckabee. "That's just being realistic."

Another fiction, Huckabee said, is that you can move fat away from a problem area.

"When I wanted to reduce my stomach, I had to do an all-over conditioning program to get that fat tissue to shrink," she said. "Cardio will burn the fat over all. After that, you can work on sculpting an area with resistance training."

Burke said one of the biggest fitness myths is that crunches can banish belly fat.

"You build your six-pack in the kitchen," she said, while noting that no one will see even the most developed abdominals if they're hiding under a layer of fat.

Moira Merrithew, co-founder of Merrithew Health & Fitness, said one of the most common misconceptions is that it's always good to stretch before a game of football or a run.

"For some athletes probably the worst thing they can do is stretch before they run," said Merrithew, who is based in Toronto, Canada.

"There's simply no hard and fast rule," said Merrithew, a former dancer. "Pilates is good for dancers before they go out, because it mobilizes the joints. There are so many effects that stretching can and cannot have. There are limits to really pushing that stretch."

And even the most dedicated couch potato cannot turn muscle to fat, according to Carol Torgan, a consultant exercise physiologist with the American College of Sports Medicine.

"Muscles and fat are two different types of cells. It would be like turning apples into oranges," she said.

More troubling is the fallacy that one can never drink too much water.

"It can result in a condition known as hyponatremia, in which there is an imbalance of water to salt," Torgan said. "This is also known as water intoxication or over-hydration, and can be extremely serious."