What’s worse than not working out at all? Spending your time doing exercises that don’t work. All forms of physical activity are good for something. But if you’re working toward a specific fitness goal, such as fat loss, it’s important that you use your time at the gym wisely.

Here are some of the worst exercises for burning fat, and the best workouts to replace them.

1. CRUNCHES

Why they don’t work: If you happen to enjoy lying flat on your back and setting your core on fire without noticeable results, keep at it. Doing crunches is not going to get you that six-pack you’ve always wanted. For optimal fat loss, you’ll want to go a few steps further to burn more calories while building more muscle.

What to do instead: When in doubt, do plyometrics. Plyometrics will help you burn through fat like you won’t believe. Learn how to make plyo part of your fitness routine.

2. PILATES

Why it doesn’t work: Pilates, like yoga, is great for improving flexibility and your mental health. Because it helps you gradually build and strengthen your muscles, it can be a great way to prevent getting injured while training. If you want to relax, do pilates. If you want to strengthen your core, do pilates. Don’t do pilates if you want to burn fat.

What to do instead: Try a once or twice-per-week spinning class. Spinning incorporates a little bit of everything – cardio, resistance training; your full body is definitely getting a good workout. It’s not effective for fat loss if it’s the only physical activity you do, so mix up your workouts to burn fat most effectively.

3. THE ELLIPTICAL

Why it doesn’t work: Elliptical machines can benefit you in a number of ways. They’re a great low-impact machine to use if you’re trying to take it easy or recover from an injury. Working out on an elliptical still gets your heart rate up, so it’s absolutely perfect if you’re trying to get back into (or start) a fitness routine. It’s not too intimidating. But it does virtually nothing for fat loss, since it’s such a low-intensity machine. You can make any machine bend to your interval training will, but you’re much better off using something else if that’s your workout plan.

What to do instead: HIIT is your best replacement here. Short bursts of energy expenditure will make you burn calories like crazy. The more calories you burn, the more likely you are to lose fat. Just be aware of the biggest fat-burning fitness myth!

Fat loss isn’t so hard, once you know how to make the most of your gym time. What are you waiting for? Get out there and start sweating.