Chances are, you’ve heard friends, media, and the medical community spew some running “facts” over the years. Running is great for weight loss. Running will ruin your knees. Running will make you too skinny.

It’s not always easy to determine fact from “common belief” so we’ll dispel these running myths with the researched facts, courtesy of a chapter excerpted from the new book, Run Your Fat Off, by Jason R. Karp, Ph.D. (Reader’s Digest, March 2017).

The book also includes calorie-burning runs to help you lose fat, daily running and eating plans for runners of every level, and expert running tips throughout.

Here are some of the most common myths Karp has heard in his career as a running coach, and why they’re wrong.

MYTH: Running is bad for your knees

Perhaps the biggest myth about running is that it messes up your knees for life. If I had a nickel for every person who’s ever asked me about my knees and commented on running being bad for them, I’d have enough nickels to pay the Kenyans’ expensive race appearance fees. Why would an activity humans evolved to do be bad for our bodies? If running were harmful to your knees, evolution would have eliminated the ability to run a long time ago because only traits that confer an advantage survive. People assume that pounding the ground with your legs with so much force must be jarring to your joints. But, if you run correctly, you shouldn’t be pounding the ground. You should be rolling through each step, skimming the ground like a pebble on the water, with your body in perfect alignment and your feet landing underneath your hips. Running shouldn’t be a jarring activity. When done right, it’s smooth and fluid.

Also, the research simply doesn’t support that running is bad for your knees. People who run have no greater incidence of joint problems or osteoarthritis than people who don’t run. If you have a family history of joint degeneration—if both your parents have had knee replacements or if you already have knee problems when you move a certain way or do certain activities—running can bring that genetic predisposition or those latent issues to the forefront. But running, per se, isn’t the underlying cause of your joint problems. As long as you have healthy knees, running isn’t bad for them.

MYTH: Running will make me scrawny

Because running is a lower-body exercise, many people think that they’ll get scrawny arms by running. Although it’s true that running is a much better stimulus for the legs than it is for the arms, your arms are still very active when you run because your upper body must counterbalance the movements of your lower body. Runners typically have defined shoulders because of the repetitive movement of the shoulder to control the arm swing. Runners come in all shapes and sizes. Not every runner looks like a scrawny Kenyan or Ethiopian. In fact, the only runners who look like the Kenyans and Ethiopians are the Kenyans and Ethiopians. You’re not going to become scrawny because you run a few miles every day. Even if you run 50 or more miles per week, you’re not going to look scrawny. If you’re concerned about getting puny arms, include resistance training a couple of times each week for your upper body. Here’s how to run stronger and longer.

MYTH: More expensive running shoes are better

Never be influenced by a shoe’s price tag. More expensive doesn’t necessarily mean better. There are plenty of great running shoes for less than R1000, especially if you buy them at a general sporting goods store instead of a specialty running store. A higher price can mean that the shoe has more technology, or it can simply mean that it’s a flashy new model with a high markup price. Most runners don’t require all the bells and whistles found in fancy shoe styles. The best shoe for you comes down to what you need for your foot type and running mechanics. Look for a shoe that matches your level of pronation (how much your foot rolls inward when it lands), and feels comfortable right out of the box.

MYTH: Don’t run if you have a cold

Exercise and your immune system have an interesting relationship. Moderate amounts of exercise on a regular basis strengthen your immune system and give you resistance against colds and other upper respiratory tract infections. However, long and intense running can actually weaken your immune system because of the stress it puts on your body. Catching a cold or getting the flu when you run a lot or train for an event like a marathon is very common because your immune system becomes compromised. To help defend against colds and flu, consume both simple and complex carbohydrates (fruits, bread, potatoes, and pasta) as part of your normal diet. Carbohydrates provide energy and also strengthen your immune system by limiting the rise in stress hormones following your workouts. If you do get sick, here’s the golden rule: If the symptoms are above your neck, it’s okay to run—just don’t try to do a difficult workout or a long run. If the symptoms are below your neck, like a sore throat, coughing, wheezing, or a fever, you shouldn’t run.

MYTH: Running on an empty stomach burns more fat

The problem with this myth is that it’s true, at least technically. Muscles will indeed use more fat if you run when your blood glucose is low, as it can be first thing in the morning after an overnight fast. But burning more fat during your runs doesn’t necessarily mean that you will lose more weight. Running when fasted before breakfast may help you reduce the total number of calories you consume throughout the day, but it doesn’t allow you to cheat the laws of caloric balance; at the end of the day, you still have to have a caloric deficit to lose fat.

When you run first thing in the morning before breakfast, your muscles don’t just rely on fat immediately. When running at a slow or moderate pace, they’ll use some fat, just like they would when you run at any other time of the day. But they’ll also use whatever carbohydrate is available from blood glucose and stored glycogen because carbohydrates are muscles’ preferred fuel. When you run out of glucose, your muscles will then start to rely more heavily on fat. But running on an empty stomach with low blood glucose decreases the intensity at which you can run, which results in a lower-quality workout and less total calories burned. For weight loss, it really doesn’t matter if the calories you burn when you run come from fat or carbohydrates; how many total calories you burn when you run is what matters. If you have a light breakfast containing carbohydrates of about 200 to 300 calories about 30 to 60 minutes before you run, you’ll feel better and have a higher-quality workout, which will ultimately help you burn more calories. If you can’t wait that long, consume something easily digestible, like a banana or a slice of toast with peanut butter.

MYTH: You have to run in your fat-burning zone to lose weight

People often assume that low-intensity exercise is best for burning fat. Cardio equipment manufacturers contribute to this assumption by posting a “fat-burning” workout option on their front panels, which influences people to choose that option because, after all, people want to burn fat. During exercise at a very low intensity, such as walking, fat does account for most of the energy you use. At a moderate intensity, running at 80% of your maximum heart rate, fat accounts for only about half of the energy you use. While you use both fat and carbohydrates for energy during exercise, these two fuels provide that energy on a sliding scale—as you increase your intensity, the contribution from fat decreases while the contribution from carbohydrate increases.

While you use only a minimal amount of fat at faster paces, the number of calories you use per minute and the total number of calories you expend are much greater than when you run at a slower pace, so the amount of fat you use is also greater. Research has shown that the highest rate of fat use occurs when you run at a hard aerobic pace, like the tempo runs. What matters is the rate of energy expenditure rather than simply the percentage of energy expenditure derived from fat. Since you use only carbohydrates when you run at a high intensity, does that mean that if you don’t run fast, you won’t get rid of that flabby belly? Of course not.

Despite what most people think, you don’t have to use fat when you run to lose fat from your waistline. The little amount of fat that you use in combination with carbohydrates during moderate-intensity exercise is in the form of intramuscular triglycerides—tiny droplets of fat within your muscles. Adipose fat (the fat on your waistline and thighs) is burned during the hours before and after your workouts while you’re sitting at your desk. For fat and weight loss, what matters most is the difference between the number of calories you expend and the number of calories you consume. So don’t worry about running in your fat-burning zone, because there’s no such thing.