Everyone likes to preach about the best workouts. (How much can you squat, bro?) But part of a good workout is also understanding what constitutes the worst things at the gym—from ineffective to a straight-up injury risk—and what to steer clear of. In an effort to help you better navigate the gym, we called up Dan McCarthy at Crow Hill CrossFit in Brooklyn and chatted about the least effective exercises and what you should do instead.

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Why they're bad: "Crunches put unnecessary stress on the lower back and are just generally ineffective at working the abdominal muscles."

What to do instead: Hollow Body Hold, a stability exercise that will absolutely cook your core. "Lie on your back, and use your core to try and pull your belly button through to the ground, and let that raise your legs and shoulders off the ground a few inches, effectively creating a slight crescent moon shape with your body. Hold this position for 1 minute. For an added challenge, try and rock your body back and forth, without kicking with your legs at all. Pretend you're made of rock."

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Why they're bad: "While they can help you gain some size in the biceps, you are also isolating one specific muscle group and not letting all the surrounding muscles do their part. The body moves as a unit, never in isolation, so why not train it that way?"

What to do instead: Chin-Ups. That's right, it's gym class all over again. "You'll get a better bicep pump by performing sets of strict chin-ups, and you'll also be strengthening your lats and traps at the same time," McCarthy says. "Who doesn't love a chiseled back?"

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Why it's bad: "One of the worst things you'll find in a gym" McCarthy says of the guided squat rack. "This is meant to help you squat safely, but unfortunately it does just the opposite. It doesn't let the bar path move, as it should in an actual squat. It forces you into unstable and unsafe positions, improperly loading your spine and hips."

What to do instead: Uh, actual squats! "Set your feet a little wider than hip width with your toes pointed just slightly out," McCarthy explains. "Take a barbell out of a squat rack and have it sit on your traps—not on your spine!, sit your butt back and down, while maintaining as upright a torso as you can. Make sure your knees and toes are pointing the same direction the whole time, and try and get your hip crease below your knees. Return to a standing position. Squats are the holy grail of any strength program. Just ask Arnold!"

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Why they're bad: This exercise—where you essentially extend your arm back with a dumbbell—is a longtime gym staple. But just because the guy at Gold's told you do it back in 1998 doesn't make it worth your time now. "Kickbacks put your shoulder in a poor position to move effectively, and also don't allow you to load the movement with much weight," he says. "For those reasons, the movement generally won't yield the results you're looking for."

What to do instead: Pushups. Never doubt body weight exercises! Just wait a second and listen to McCarthy's guide to proper form. "Make sure your hands are shoulder-width apart, and your index fingers are parallel with each other. Externally rotate your elbow—point the elbow joint back—and lower your chest to the ground, maintaining a solid plank the whole time. Allow your chest—but not your thighs or ribcage—to touch the ground, and then press back to the top again. This is more effective at targeting your triceps, and it also works your core and your chest!"

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Why it's bad: You might think it's low impact, but it's putting your body in wacky positions. "The elliptical takes your body through an unnatural range of motion, unlike anything your body would do in real life," he says. "Besides, any piece of equipment that encourages you to read a magazine while exercising shouldn't be in a gym."

What to do instead: Channel your inner Winklevoss and hit up the rowing machine. "If you're going to be on a piece of cardio equipment, this is where you should be," McCarthy says. "The rowing machine not only works almost every muscle in your body, but it also teaches you proper pulling mechanics. Revving the intensity up on this is a killer—try doing ten rounds of 30 seconds as hard as you can, and then 30 seconds of light rowing."

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Why it's bad: Unless you're rehabbing an injury, steer clear of isolation exercises. "The leg press is an isolation exercise than places unnecessary strain on the lower back and doesn't allow for proper muscle recruitment in the legs," McCarthy says. "This can lead to all sorts of injuries of the knee and back."

What to do instead: Squats. Yes, more squats. "Once again, we find ourselves back at the squat rack," McCarthy says, laughing. "Load that barbell with a weight you can comfortably handle for three sets of five reps. Next time you squat, add five pounds to that weight, and do your 3x5 again. Continue this progression, squatting three times a week, and you'll find yourself getting extremely strong extremely quick."