By Marnie Kunz, NASM-certified personal trainer, USATF- RRCA-certified run coach

Unfortunately, fitness myths are everywhere these days. Whether you’re scrolling social media or getting blasted with a commercial on YouTube, it’s hard to avoid the common misconceptions about fitness, weight loss, muscle mass, and more. As a trainer and running coach, and also a journalist, I have to deal with fitness myths a lot. Whether I’m training people or looking for workout information for an article, I come across many false statements about fitness. I see claims about miraculous muscle growth, six-pack abs, and magic pills for weight loss. Sometimes people are just misguided and misled and other times they’re trying to sell harmful yet lucrative products or services.

This guide will uncover the 10 most common fitness myths and offer scientific evidence to debunk them. I will also highlight credible fitness resources that can give you helpful, in-depth fitness information that is backed by science.

10 Biggest Fitness Myths Debunked

Myth 1: Muscle turns to fat when you stop working out.

This is one of the most common fitness myths that I hear from people I train. A lot of people are afraid of lifting weights because they think when they stop, the muscle they gained will turn to fat. They're afraid of weight gain when they don't work out. This is like saying wood turns to plastic. Muscle is composed of different materials than fat and cells do not convert from one type to the other.

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The truth is that if a person stops lifting weights and becomes completely sedentary, they will lose muscle tissue as the muscles shrink. Fat will build up in the body more quickly for a sedentary person, so if you consume more calories than you burn and do not use your muscles much, you will gain overall body fat. But this does not mean your muscles turn to fat and is not a reason to avoid weightlifting. People miss that the sedentary lifestyle is to blame for gaining fat, not weightlifting.

There are many benefits of weightlifting, from boosting your metabolism to strengthening bones and muscles and improving brain health. Do not believe any fitness myths that discourage you from weightlifting or other forms of strength training.

Myth 2: Lifting weights makes you big.

This is another common fitness myth that turns people away from weightlifting, especially women. People see muscular powerlifters and huge guys at the gym and think that lifting weights will make them look like that. Then they turn ro aerobic exercises only. The truth is that weightlifting does not make you bulky unless you specifically follow a bodybuilders program, which would require hours of targeted heavy lifting, a special diet, and very involved, targeted workouts that you would do for years, and even then, building muscle is very hard, even harder for women than men.

General strength training exercises and lifting heavy weights for standard reps (between 5 to 15 reps) will not make you bulky. This myth is so damaging and has made millions of women lose out on the benefits of weightlifting due to an unfounded fear of looking “bulky.” In reality, weightlifting can help everyone enjoy a better quality of life by preventing injuries and diseases, improving balance and coordination, building confidence, and boosting metabolism.

Myth 3: You can target your abs (or another specific area).

This is another one of the most prevalent fitness myths. People will say they want to “lose belly fat,” or “tone” their abs, get six-pack abs, or practice spot reduction for their or another body part. The term “tone” has been used for decades to target women who are afraid of building muscle, but the reality is that in order to make muscles look defined, you need to build muscle tissue through strength training.

Check out my post on women’s muscle-building workouts to get started with strength training for women.

Another false part of this myth is that you can selectively lose fat and “tone” target body parts. The truth is when you lose weight, you can’t pick where the weight comes off, and you can’t selectively sculpt certain body parts without doing full-body exercises. There are no miracle exercise machines that will transform just one area of your body.

In order to lose fat, you will need to follow a weight loss program with an exercise routine that includes regular workouts and healthy eating.

You can strengthen certain body parts and build lean muscle tissue, but you cannot just do a “flat ab workout” that will make you lose belly fat and get a six-pack without working the rest of your body. Getting a six-pack involves doing regular cardio and strength workouts, as well as eating healthy. Altering your body composition and losing body fat takes sustained efforts and happens all over, not in one target area.

Having certain genetics in your favor is also part of the equation for chiseled abs.

Myth 4: Pain is good.

The old saying “No pain, no gain” helps spread the fitness myth that pain is a necessary part of making fitness progress. The truth is that you may experience some discomfort or even slight pain at times when you’re working out, but the pain is not a sign of progress, and too much pain means you need to stop exercising. There is no correlation between muscle soreness and fitness progress.

Constantly working out until you are in pain is a recipe for overtraining, injury, and burnout. Not taking enough rest time hinders your muscle recovery and will be an obstacle to your fitness progress. Learning to listen to your body and stop when you feel a sharp or nagging pain can help you prevent injury or lessen injuries before they become more serious.

Similarly, a lot of sweat does not mean you’re burning more fat or getting a better workout. It just means your body is overheated and trying to cool down.

Doing dynamic stretching before a workout can help increase your full range of motion, reduce soreness and prime your muscles for exercise. After working out, static stretching can also help improve your muscle recovery and ease soreness.

Myth 5: If you aren’t sore, you didn’t get a good workout.

This is one of the fitness myths that goes along with the pain misconceptions. People often think if they feel sore after a workout, their muscles are getting stronger and they are making fitness progress.

The best way to make fitness progress is to follow a fitness program that uses progressive overload, which gradually increases your intensity or duration of exercise to improve your fitness level.

While it’s common to feel sore and experience DOMS (delayed onset muscle soreness) in the days following a new workout or after increasing your intensity, soreness itself is not an indicator of your fitness progress or fitness level. And if you experience too much soreness, where you can’t work out the sore body parts two or three days after a tough workout, you trained too hard and your body will have a hard time with adequate muscle repair.

Myth 6: Never quit.

This one is a favorite of Hollywood, fitness ads, and American culture in general. The idea that you should never quit and push through any pain can be very damaging, mentally and physically. There are many cases in which it’s important to quit an exercise, including when you’re injured or mentally burned out.

It’s not worth risking your health and happiness to pursue exercise at all costs and is very extreme when you think about it. Animals know to rest when they’re injured or sick and humans need to do the same. Any coach or trainer who tells you to push through injuries or intense pain is giving you dangerous advice that could seriously damage your muscles or joints.

Myth 7: Keep doing the same workout to get different results.

Another common fitness myth is that you should do the same workout over and over. When I train people, many have gotten into a rut with their workout routines. They may be running the same distance and pace every day or doing the same bodyweight workouts. For weightlifters, they may use the same amount of free weights day in and day out without change. This is fine if you want to maintain your current fitness level but you will not make performance gains if you keep repeating the same workout.

If you want to become a stronger athlete or increase your fitness level, you will need to add intensity or duration to your training. The Principle of Progression states that you can increase the time, weight, or intensity of your workouts by up to 10 percent or less each week to allow your body to gradually adapt to training. This helps reduce your risk of injury while also pushing your body to perform at higher levels.

Myth 8: You can eat anything if you exercise enough.

I wish this were true but the fact is that even if you run a lot, lift weights, or do other exercises, you can’t eat absolutely anything without gaining weight. Runners often think when they run far, such as training for a marathon, they can eat unlimited calories and junk food. The truth is that everyone needs a certain amount of nutrients to function well and an active lifestyle requires even more nutrients.

Eating processed snacks and junk food will give you a lot of empty calories with little to no nutrition. Check out our nutrition section for help balancing carbs, protein, and fats and getting the nutrients your body needs to function well.

Myth 9: Women need different exercises than men.

This is one of the fitness myths that frustrates me the most. As a female trainer, it’s hard to see how many women miss out on the benefits of strength training due to gender stereotypes that say women shouldn't lift weights. The fitness industry has made billions of dollars from targeting women with classes to lose weight and “tone up” when in fact women need the same workouts as men to be healthy.

Adults of all genders need at least two strength training sessions a week and 150 minutes of moderate cardio exercise, according to the Physical Activity Guidelines for Americans.

Myth 10: Pre-workout is necessary.

Pre-workout is just a marketing phrase coined by the billion-dollar supplement industry. If you need energy for your workouts, you should get it from healthy foods. You do not need to take any caffeinated, sugary, chemical concoctions that are part of a largely unregulated industry. I sometimes recommend protein smoothies for people who need more protein in their diets to help with building muscles and muscle recovery but the “pre-workout” mixes that have creatine and other ingredients are not necessary for the general population.

Generally, you don’t want to exercise on an empty stomach as you’ll have less energy and power. If you are hungry before a workout or run, the best time to have a healthy snack or meal is at least 30 minutes before your workout. However, individual digestion can vary so you may be able to eat more or less before working out. Experiment with healthy, minimally processed foods that don’t upset your stomach before a workout.

Credible Fitness Resources

In general, government websites, hospitals, educational institutions, and academic research sites are good places to get science-backed information on fitness and health and avoid the most common myths. Here is a list of some of my favorite sites for credible fitness information:

Random Fit podcast, produced by the National Academy of Sports Medicine. This is one of my favorite fitness podcasts for helpful, science-backed information on training, hosted by NASM-certified trainers Ken Miller and Wendy Batts.
NASM Blog is the official blog of the National Academy of Sports Medicine. The blog has lots of helpful resources and information on all things fitness-related.
ACE Fitness Blog is the official blog of the American Council on Exercise. This blog has insightful training resources and tips.
Harvard Health Blog publishes health studies, tips, and information.
CDC Physical Activity Resources include guidelines, statistics, studies, and tips on fitness and health.
MedlinePlus is a service of the National Library of Medicine (NLM), the world's largest medical library, which is part of the National Institutes of Health (NIH). The site includes lots of helpful resources and information on fitness and health topics.

What are some of the biggest fitness myths have you come across? Comment below and tag us on the Runstreet Instagram to share your training and get cheered on.

Marnie Kunz is a NASM-certified trainer and USATF- and RRCA-certified running coach based in Brooklyn, NY. Marnie likes helping people get and stay active to enjoy a better quality of life. When she’s not doing fitness things, Marnie enjoys exploring with her dog, a mischievous rescue Akita.

10 Common Fitness Myths Debunked