There were two lat-pulldown stations positioned next to each other in this gym I belonged to many years ago. On one of them was an older woman who was lifting, if memory serves, 10 pounds. I can only assume that she misread the name of the exercise and thought it was a lap pulldown, because that’s where the bar ended up when she rolled it down the front of her torso.

On the adjacent machine was a guy who was lifting, if memory serves, the entire weight stack, or most of it. He rose off the seat at the beginning of each rep to help him get the stack moving, and then leaned back at a 45-degree angle to get the bar to his chest. The deeper he got into his set, the more momentum and body English he employed.

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Two people, two completely different ideas about how to do one of the simplest exercises in the gym. And both of them completely wrong.

If you walked into that same gym today, chances are you’d see multiple versions of exercises hardly anyone did a decade ago, like planks and kettlebell swings. Those are in addition to the classic exercises, the simple ones that every lifter has done as long as he’s been lifting, but may not be doing in a way that helps him reach his goals.

“There’s more free information than ever, and yet form hasn’t improved,” said Nick Tumminello, author of the upcoming “Building Muscle and Performance: A Program for Size, Strength, and Speed,” and a trainer based in Fort Lauderdale. “Men are stubborn, and they always think they know better.”

Flawed exercise form really comes down to three basic problems:

•   Lack of control

•   Poor stability

•   Misunderstanding the point of the exercise

Let’s tackle them in that order.

Control issues

“Most people are in the gym to do bodybuilding,” Tumminello said. That is, to build muscle. But most guys in the gym train like weightlifters, where the goal is to lift the weight. There’s a big difference. “Bodybuilding is about controlling the weight through the entire range of motion.”

Take the lateral raise, for example. The way most guys do it, Tumminello said, is to “swing the weight up, and let it crash down.”

But the entire point of the exercise is to target the middle part of the deltoid muscles. To make them grow, you need to put them under tension. They’re under the most tension at the top of the range of the motion—“the part everyone cheats through,” he says.

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You see this over and over in exercises designed to target specific muscles, including the lat pulldowns I described at the beginning. Tumminello also mentioned the bent-over barbell row: “They’ll pull it halfway with good form, then jolt it the rest of the way.”

He offers a simple fix:

Select a weight you can hold at the point of maximum tension, with good form.

“If you can’t hold it four to five seconds, then the weight’s too damned heavy,” he said. “You don’t need to hold it when you train, but that’s how you should test it.”

For most bodybuilding exercises—lateral raises, lat pulldowns, bent-over or seated rows—you can test your weight at the end of the range of motion. For biceps curls, it’s the midpoint, when your forearms are parallel to the floor.

Or you can make it simpler, and just remember which part of the lift you typically have to cheat to get through. If you can’t hold it there for a few seconds, try using a lighter weight.

Bad posture

Picture these four exercises:

•   Plank

•   Pushup

•   Loaded carry

•   Bear crawl

What do they have in common? If you answered, “They’re all the same exercise,” you’re a lot smarter than me. It never occurred to me until Alwyn Cosgrove, my coauthor on the “New Rules of Lifting” books, explained it.

Of course they don’t look alike. But the key to good form is exactly the same: Whatever your posture is standing up straight, that’s what it should be when you’re doing a plank, or a moving plank (aka pushup), or a walking plank (aka loaded carry), or a scooting plank (aka bear crawl).

On the plank, pushup, and carry you should be able to draw a straight line from your ears through your shoulders, hips, and heels. On the bear crawl, the line should connect your ears, shoulders, and hips, with your torso parallel to the floor.

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The most common mistakes are postural. With the plank, pushup, and bear crawl, you see these almost every day:

•   sticking your butt in the air

•   letting your stomach sag toward the floor

•   lifting your head to check out the form of the person in front of you

On a pushup, you can tell if you’re lifting your butt when your nose reaches the floor ahead of your chest. If your stomach is sagging on a plank or pushup, you’ll probably feel it as an uncomfortable strain in your lower back. And if you find yourself mesmerized by the person in front of you on any of these exercises, you’re probably lifting your head.

The biggest problems on loaded carries come when the weight is held to one side, as in a suitcase carry. Mistakes might include:

•   Bending to the side holding the weight

•   Overcompensating for the weight by bending to the opposite side

•   Leaning back and flaring your rib cage out

You can self-correct the first two issues by paying attention. If you’re sober, you should be able to tell if you’re standing up straight. If it’s a struggle, lower the weight.

A good self-check for the latter problem is to place your non-weight-bearing hand on your sternum. If you feel your bottom ribs start to move forward, adjust your posture.

Cognitive failure

Return for a moment to the confused woman at the lat-pulldown station, the one pulling the bar down to her hips. Clearly, she didn’t understand that the goal of the exercise is to engage muscles in her middle and upper back, and to do that she needed to select a somewhat challenging weight and pull the bar to her chest.

I remembered it because it’s not something you see every day.

But there are a few commonly misunderstood exercises you’ll see on a regular basis. Tumminello mentioned the hanging knee raise. As ab exercises go, it’s about as hard-core as most of us will ever get. But that’s the problem: Most of us can’t actually do the exercise correctly.

To do it right, Tumminello said, you need to tilt your pelvis upward, something that’s hellaciously difficult from a dead hang. Instead, most guys will just lift their knees, a movement that works the hip-flexor muscles on the front of the pelvis but doesn’t work the rectus abdominis, the six-pack muscle, through the intended range of motion.

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If you can’t do that pelvic tilt—and as I said, few of us can—then you’re much better served by doing the reverse crunch from the floor or an incline bench.

Another common mistake involves exercises for the opposite side of the torso. When you do a kettlebell swing, the goal is to move the weight by straightening your hips. That engages the powerful glute and hamstring muscles. Your arms and shoulder are just along for the ride.

But before you can straighten your hips, you have to load them by pushing them backwards. If you don’t do that, you can’t generate the force necessary to swing the weight out in front of you. That’s why you see so many people turn the swing into a front raise: they’ll kind of squat down, and then pull the weight up overhead using their shoulder muscles.

A good swing, by contrast, should end up somewhere between waist and chest height. One way to tell if you’re getting it right: the bell goes just a little higher than your hands at the top of the swing. If you’re lifting it with your arms and shoulders, it’ll do the opposite, and end up below your hands. (For a full tutorial on how to do the exercise, check out The Right Way to Do a Kettlebell Swing.)

How to do any exercise better

The lessons of these nine exercises—lateral raise, bent-over row, plank, pushup, bear crawl, loaded carry, lat pulldown, hanging knee raise, kettlebell swing—can be applied to any exercise you try. You just need to ask yourself three questions:

1. What is the point of the exercise?

If the goal is to build muscle, then focus on creating tension in the targeted muscles, and don’t use momentum to blow through that part of the exercise.

2. What should my body look like while doing the exercise?

This is trickier, because on many exercises it’s hard to check your form without breaking form to look at yourself. And that’s only if you have a mirror nearby. Without one, you have to pay attention to your body’s signals. If you feel a strain in your lower back on a plank or pushup, that’s your cue to work on your alignment.

3. What actions should and shouldn’t be involved?

This is even trickier, and may require coaching, or at least some reading outside the gym. Most people looking at a kettlebell swing would think the goal is to lift the weight up in front of you, so it makes sense that you’d use your arms and shoulders. If nobody tells you it’s all in the hips, how would you know?

Which brings me to perhaps the most reliable cue: When other lifters stop, stare, and then shake their heads as they walk away, you can be pretty sure you’re doing something wrong.

Lou Schuler is an award-winning journalist and contributing editor to Men’s Health. Check out his new book “Strong: Nine Workout Programs For Women to Burn Fat, Boost Metabolism, and Build Strength For Life,” with coauthor Alwyn Cosgrove.

This article originally appeared on MensHealth.com.