There's a time and a place for three-pound weights. (Um, like when you're blow-drying your hair.) But lifting heavy is what will actually help you build muscle, turbocharge your metabolism, and prove to yourself that you are, in fact, a badass.

So how do you know if you're pumping big enough weights to really build strength and sculpt muscle? Well, lifting heavy means whatever feels heavy to you. It’s about challenging yourself and moving more weight than you could last week or month, says St. Louis-based personal trainer and strength coach Kourtney A. Thomas, C.S.C.S. In short, as long as you’re pushing yourself, you’re lifting heavy.

That being said, there are hard and fast rules about how to safely and effectively sling big weights. Here's what you need to know before tossing your teeny 'bells in favor of the big kahunas. 

1. Master Form First

Before you try to squat as much as you possibly can for six reps—or even one rep—you need to master bodyweight squats, dumbbell squats, and sub-max barbell squats (a.k.a. not-so-heavy barbell squats)—and all with perfect form, says Baltimore-based strength coach Erica Suter, C.S.C.S. Think about it: If you have “meh” form when you’re moving an amount of weight that feels easy to you, your form is going to completely break down when you’re moving a really challenging weight, she says. And that's when injuries happen.

So get the basics down before ramping up the weights. If you aren’t sure if you’re doing something right, don’t hesitate to ask a trainer at your gym to look at your form.

Get started by using just the weight plates—try the moves in this video: 

preview for 10 Weight Plate Exercises To Tone Every Muscle

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2. Slowly Up the Weight and Dial Down the Reps

“Once you have the form down, don’t be afraid to push yourself and struggle through a few reps,” says Suter. The important thing is to progress slowly. Over the course of weeks and months, not days, increase your weights and decrease your reps from 15, 12, or 10 down to eight, six, four, or if you want, even lower to approach your one-rep max. (That's a shorthand way of saying “the most weight you can possibly move with proper form for just one rep.”) As you get closer to your one-rep max, you'll also want to perform fewer sets (think two to six). 

While performing six to 12 reps of a given exercise will help you build muscle, hitting six reps or fewer (at super-heavy weights) will help you build pure strength.

“Your effort should feel hard, at least an eight on a scale of one to 10,” says Thomas. “When you get to the top of your rep range, it should feel like you have maybe one more rep left in the tank. You can then work up from there as you're ready and your strength progresses.” When it comes to safety, a good rule of the weight room is to increase your weights in a given exercise only after you’re able to perform two extra reps of that exercise for at least two weeks in a row.

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3. Go Heavier on “Big Lifts”

Like we said, lifting six reps or less with as much weight as possible is great for improving strength. But you only want to go really big while doing compound lifts—squats, deadlifts, lunges, and Olympic lifts like cleans—that involve multiple muscles and joints, says Suter. 

Why? Because, when you perform these compound movements, the force is spread out between so many muscles, connective tissues, and joint structures that everything gets worked just the right amount. Nothing gets overstressed, she says. But if you try to curl your one-rep max, you run the risk of injuring your biceps and your elbow joints—either all at once or over time, explains Sam Simpson, C.S.C.S., C.P.T., co-owner and vice president of B-Fit Training Studio in Miami. The same goes for other isolation exercises like calf raises, glute kickbacks, and triceps extensions.

And while some moves like bent-over rows definitely qualify as compound movements, they aren’t really conducive to near-max loads. After all, even if your lats can handle a 75-pound weighted barbell, that doesn’t mean that you won’t tip over when you bend over to start the movement, says Suter.

So once you work up to it, go ahead, lift really heavy loads (six reps or fewer)—but only when performing sturdy, compound lifts. With anything else, cap the weight at something that you can handle for eight reps at a time. (Learn more about how to master your lifts with Women's Health's Lift to Get Lean by Holly Perkins!) 

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4. Get Some Rest

When you’re pushing your body with heavy lifting, you need to think about factoring rest into your overall workout routine—likely in a way that you’ve never had to before. After all, this isn’t circuit training, and 30 seconds of rest between each set or exercise just isn’t going to cut it. It’s important to realize that the heavier the loads you lift, the more time your body needs to replenish energy stores, recover, and be able to rock the next set, Simpson explains. For example, if you’re lifting eight to 12 reps per set, you’ll likely need about 60 seconds of rest between sets. Perform six to eight reps per set and you'll need 60 to 90 seconds of chill time before going again, he says. Go even heavier and you’re looking at two to five minutes of rest.

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What’s more, when you look at your general workout routine, you need to incorporate not only heavy, but also moderate and light workout days. Some lifters like to achieve that by lifting really heavy for a few weeks, then giving themselves a light week for recovery. Others like to have one heavy, one moderate, and one light day a week, switching up their sets, reps, and weights from day to day, says Suter. Still, others prefer to stick with the same reps and sets during every workout, just lifting slightly lighter weights on moderate days and even lighter ones on aptly named light days. Listen to your body and do what works for you.