If you’re taking the time out of your busy day to get to the gym, you want every moment to really count. But if you’re dedicating any of your precious gym time to less-than-effective exercises, you’re probably cheating yourself out of the results—like building muscle and burning fat—that you’re after.

We asked trainers to share the most eye-roll-worthy moves in the game—and what you should be doing instead—so you can have more efficient workouts and become your fittest, healthiest self.

 1. Smith Machine Squats

The idea of the Smith machine makes a lot of sense: By using a barbell that’s attached to fixed tracks, people who are afraid to do barbell squats can feel more comfortable working on the important movement, says Todd Nief, C.S.C.S., owner and founder of South Loop Strength & Conditioning in Chicago.

The thing is, the way the Smith machine’s bar moves forces you into a movement that’s not really a squat. “Most people end up doing some sort of bizarre knee-folding movement,” says Nief. The direction of the barbell track can force you to shift your weight forward and put extra stress on your knees and back, which not only prevents you from learning proper squat form, but also puts you at risk for injury.

Related: 3 Ways To Improve Your Squat

The Smith machine may be useful for bodybuilders targeting specific muscle groups, but for most people it just forces them into pretty unnatural movement patterns, says Nief. Working on other variations of squats, like goblet squats or jump squats, will do more to improve your technique and your results.

2. Upright Rows

“Upright rows are one of my least favorite moves,” says Katie Dunlop, C.P.T., founder of Love Sweat Fitness in Orange County, California. This exercise puts your shoulders in a compromising position and puts unnecessary stress on your wrists, making it more likely to land you with an injury than the boulder shoulders you’re after.

For a more effective (and safe) shoulder burn, Dunlop recommends sticking to your standard dumbbell shoulder press. If you want to hone in on your rear delts (the backs of your shoulders), swap in dumbbell reverse flies instead.

3. Basic Crunches And Sit-Ups

There are two major issues with these classic core moves: they only focus on the rectus abdominis (or ‘six-pack’) muscles and they’re often performed incorrectly.

“People typically rely too heavily on pulling themselves up with their hands behind their head rather than with their abs,” says Dunlop. “This not only leads to potential neck or back injuries, but also means you don’t actually strengthen your core.”

Related: 4 Mistakes People Make On The Quest For Abs

Instead, choose moves that light up all 360 degrees of your core (and burn more calories), like forearm planks, mountain climbers, and Russian twists.

4. Machine Leg Extensions

If efficiency is your goal, Dunlop generally recommends avoiding weight machines, since they often allow you to use momentum you wouldn’t have when using your body weight or free weights, and tend to isolate just one muscle group.

“The other problem with exercises like machine leg extensions is that they don’t reflect movements you use in real life,” she says. Your exercises should be functional, meaning they mimic movements you might use outside of the gym—so if you want to hit your quads hard, swap those leg extensions for good ‘ole weighted squats.

5. Weighted Side Bends

It’s rare to go an entire gym session without seeing someone in the gym bending from side to side with a dumbbell or weight plate in-hand. “People think they are targeting their obliques and working their abs, but really all they are doing is putting undo pressure on their spine,” explains Danielle Natoni, C.P.T., founder of Fit and Funky.

If your obliques are top priority, Natoni recommends performing Russian twists with that dumbbell or weight plate to better activate your core without stressing out your spine. (Here are eight more moves worth trying.)

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