Picking up recommendations from friends may be a great way to keep your workout fresh, but any suggestion is only as good as the facts behind it. Your workout time is precious. Before adopting a new mindset, make sure it’s more than just another exercise myth. Here are the facts behind common fitness fictions.

Myth: Fat turns to muscle after thirty minutes of exercise.

Truth: According to Colleen M. Hacker, PhD, professor and assistant dean of the School of Physical Education at Pacific Lutheran University, it’s highly improbable that fat will turn to muscle whether you work out for thirty minutes, or three hours. “It’s completely different tissue,” she says. So why exercise? To change both fat and muscle cells, says Hacker. “Fat cells and muscle cells can enlarge and shrink,” she explains. “What happens when I exercise regularly? I don’t lose fat cells, I shrink their size. When I strength-train, I don’t create additional muscle cells, I increase the size of the cells that I have.”

Myth: Women will get bulky if they weight train.

Truth: Unless you are using performance-enhancing drugs, says Stephen A. Black, MS, a health and wellness clinician practicing in West Springfield, Massachusetts, you won’t develop huge muscles. Women can’t. You lack sufficient testosterone. So lift away, ladies. If your goal is endurance, Black recommends light weights and high repetitions. If a long, lean look is what you’re after, try Pilates, swimming, or t’ai chi.

Myth: Skinny people are fit people.

Truth: “The notion that our body size is somehow indicative of our overall health . . . just isn’t so,” says Dr. Hacker. Instead of focusing on size, she emphasizes a focus on physical activity, and the research backs her up. “Men and women who are medically classified as overweight or even obese but who regularly exercise and are physically fit have lower all-cause death rates—even though their bodies remain above the height/weight ranges or BMI [body mass index]—than men and women who do not exercise, who are unfit but are within those desired height/weight ranges,” she says. The upshot? Spend less time on the scale and more on the bike.

Myth: To build muscle I should eat as much protein as possible.

Truth: “Protein doesn’t build muscle. Strength training along with an adequate diet that includes protein helps stimulate muscle growth,” says Heidi Skolnik, MS, sports nutrition consultant to the New York Giants. Protein is necessary—and is especially helpful when beginning a new workout regimen, but overall caloric intake is more important, she says. Your best bet? Have what Skolnik calls a “recovery meal,” carbohydrates and protein, within 15 to 20 minutes of a workout’s end.