To many, the world of working out can seem like it’s full of rules. Keep your back flat during a push-up, squeeze your glutes in a plank—and don’t forget to roll your shoulders down before performing a bodyweight squat. Sure, these pointers are helpful and keep us from getting injured. But if you’ve ever wondered “WTF did he just say?” during a group class, you’re not alone.

Turns out, there’s plenty of bad advice out there. And those who spend their days in the gym hear a lot of it. We asked top trainers to cut through the fog of misinformation and tell us the worst tips they’ve ever heard. If you’ve followed any of this advice, now’s the time to start thinking differently.

1. Heavy weights will bulk you up.

“People worry that lifting heavy weights will bulk them up—it’s not going to happen! This is a constant battle with many of my female clients. This bad advice deters women from gaining strength, and building stronger connective tissue and postural muscles. When you have more muscle mass—density, not size—you increase your metabolism. I constantly advise clients to look at the research, or just check out a Victoria’s Secret model’s Instagram a few weeks before a show. They’re lifting substantial weights, doing CrossFit, and pushing themselves. The result? They all have lean, toned limbs.” — Nick Hounslow, spin instructor and star of E!’s Hollywood Cycle

2. There’s only one way to do the perfect squat (or lunge).

“I continue to hear personal trainers and fitness experts who say there’s a single way to do a lunge or squat. I see them correcting chest alignment and where the knees line up with the toes or ankles. This fails to take into account physics and the person’s goal. There are thousands of different ways to do a lunge. What’s your goal? Strengthening the top of your thighs versus toning your thighs requires very different movement.” — Chalene Johnson, creator of PiYo

3. Working out is about living longer.

“One of my buddies told me that people who work out all the time might live longer but those extra years are wasted in a gym. I couldn’t help but laugh because it’s just another example of our impressive ability to convince ourselves not to work out. Of course, I told him I don’t work out to live longer, I work out to live better. Then I went to the gym.” — Rob Sulaver, founder of Bandana Training

4. You need to confuse your muscles to build strength.

“Varying your weight training to build muscle is a load of crap. This nonsense is called muscle confusion theory. If you constantly switch around exercises, you can’t measure progress. Measuring progress means looking at what you lifted today and comparing it to what you lifted last week. To make the comparison meaningful, you’ll need to keep the variables constant: Do the exercises in the same order and in the same routine that you did last week, and do it with almost the exact same weight. Did you do one more rep with the same weight, or the same number of reps with five pounds more? That’s progress.” — Martin Berkhan, founder of LeanGains

5. There’s an ideal weight for your body type.

“No trainer or training program should ever tell you how much you should weigh. No one has the ability or right to tell you what a proper weight is. Every body is different. You were not meant to look like anyone else and your body’s proper weight is what makes you feel confident and comfortable. Stop letting a number on the scale have so much power. Why are you letting your weight determine your happiness? You know what is healthy, fit, and sexy? Confidence!” — Jenny Schatzle, founder of The Jenny Schatzle Program

6. Workout classes are designed for all levels.

“When I was starting my career in the dance fitness world, I was told numerous times, ‘Come check out my class, it’s for all levels.’ But the actual level of the class was pretty advanced. There was no instruction given on how to modify moves and all of sudden we were throwing our bodies around, jumping, bouncing, and twisting. I realized how dangerous this was for anyone new—and the classes even left my knees and lower back screaming for an ice pack. Make sure you know the level of the class you’re walking into and don’t be afraid to talk to the teacher to let them know your personal fitness level.” — Benjamin Allen, Creator of GROOV3

7. There’s one best approach to fitness.

“I’ve heard plenty of people say there’s one right answer or best way to approach fitness. But there’s no such thing as perfect squat or push-up. The best way for each person depends on movement history (and injury history!) and their environment (what they have access to). Plus, it’s important to know what they enjoy and what they will do.” — Jen Sinkler, author of Lift Weights Faster