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THE WORST THING you can do in the gym? Go through the motions. Use the same weight for the same number of reps on the same moves for a long time, and you won’t stay the same. You’ll regress.

“As we get older, if you train like you’re trying to improve, you may get lucky and maintain against this natural degradation [of muscle and strength that comes with aging]," says Shawn Arent, Ph.D., C.S.C.S., chair of the Department of Exercise Science at the University of South Carolina.

Put another way: Even if you aren’t looking to build epic strength or massive size, you’ve got to train like you’re trying to accomplish a goal beyond just showing up. You need to use some form of progressive overload to stimulate your muscles and keep pushing them to new adaptations. If you're new to the gym, you might assume the only way to do this is by adding more weight. That's not the case. You can also tweak other factors to up the challenge—like increasing time your muscles spend under tension with techniques like pause reps or, even more simply, upping the volume with more reps.

That last technique is the most accessible—which is why lifters often pit the two general approaches against one another: More weight vs. more reps. But what’s the best way? Will your workouts and results improve if you add more weight to the bar or machine, or add more reps to each set?

How to Determine Between More Weight or More Reps

Maximize High-Quality, Pain-Free Volume

The short answer is: Yes. Your workouts and your results will improve if you progress weight or reps—as long as the sets you do are challenging.

“The more pain-free, high-quality volume you can do, the better,” says Mike Nelson, Ph.D., C.S.C.S., an associate professor at the Carrick Institute. Volume is a measure of the total amount you lift on an exercise or a body part, calculated as the weight you lift multiplied by the reps you do. Increasing volume will likely result in gains in strength, mass, and overall fitness.

But the high-quality part matters, says Men’s Health fitness director Ebenezer Samuel, C.S.C.S. “That rep that takes six seconds to get up, and you’re rounding your back and falling apart—that’s where injury happens,” he says. Whether you’re adding weight or reps to a movement, knowing when to end the set matters. That’s before your form breaks down. It’s the point where you’re getting close to—but not necessarily reaching—momentary muscle failure.

Working on sets like this can help you reach almost any goal, whether you’re adding weight or reps to get there. But for certain goals, choosing one or the other way to progress does have advantages. Here, these three experts guide you to the right way to get better.

How to Pick More Weight or Reps Depending on Your Goals

Maintaining General Fitness

More Weight or More Reps: Combine them—but push it.

Getting close to those slow, grinding reps that signal muscular failure on an exercise is the key to building strength and size, and to maintaining your general fitness. But lifting to true muscular failure takes longer to recover from, increases soreness, and can increase your chance of injury, Samuel says.

You still want to be pushing yourself so you’ll progress, however, so you need to be smart. Whether you choose to do this with more weight or more reps—or, better yet, a combination of both over time—Samuel has a two-step approach to help you stay on track and away from injury.

Step 1: Once per month, do a workout where you really push a set of an exercise. If it’s a dumbbell bench press, for example, do a few sets where you get truly close to failure, or at least try to push beyond what you can normally do. So if you’re usually lifting 55-pound dumbbells for eight reps, try one set where you go for the same reps with 60s, or where you use the 55-pounders and try for 10 reps.

Step 2: Use this new personal best with a chart to determine your new training volume for each set. Tables in free workout tracking apps like FitNotes (for Android) and HeavySet (for iOS) have charts that estimate your rep-maxes based on the maximum weight you’ve lifted at another rep amount. If your four-rep max on a barbell Romanian deadlift is 270 pounds, for example, the app will estimate how much you can lift at other rep ranges—like 255 pounds for five reps, or 220 pounds for 10 reps.

Take these max numbers, and back them off a little, Samuel says. Take five or 10 pounds off the weight listed, or a few reps off the max reps listed, and work in that range: In the above deadlift example, this could be doing sets of 245 for five, or sets with 220 for seven or eight.

A month later, do Step 1 again: Push it, and recalculate with the charts.

Gain Muscle Size

More Weight or More Reps: Either. Just make it hard.

One of the biggest misconceptions in the weight room, Nelson says, is that if you want to gain muscle size, you need to lift in the “hypertrophy range,” doing 12 to 15 reps per set.

“Some studies show that doing as little as 30 percent of your one-rep maximum can still create hypertrophy,” he says. “Others have shown that low-rep sets, even around five reps, can create hypertrophy if you can get enough volume.”

The key, he says, is getting enough volume and making sure the sets are still challenging. When a weight is as low as 30 percent of your one-rep maximum, it’s a weight you can do more than 30 times in a set.

“If that’s done appropriately, that is miserable. The sheer acidosis, the metabolic effect of that… it’s uncomfortable,” Arent says. His lab has performed studies of these kinds of high-rep sets, and while they’ve been able to create muscle gains, the study participants are often surprised. “Light load does not mean easy. It’s still got to be a near-maximal effort by the end of that set.”

Nelson and Arent’s tip: Whether you prefer sets of five, eight, 15, or another number, make it hard, and you’ll gain muscle. Find a sweet spot that’s allows you to rack up volume without getting bored trying to count all your reps.

Gain Absolute Strength

More Weight or More Reps: More weight

Lifting light and heavy both build muscle, but strength is different. When exercise scientists have pitted weight versus reps, participants get stronger when they lift heavier. A 2016 study published in The Journal of Sports Science and Medicine found that when a group of 19 resistance-trained men trained three times per week for eight weeks with sets of either two to four reps or eight to 12 reps, the guys with the shorter, heavier sets gained more strength—even though the volume lifted was the same.

Notably, both groups got stronger—and that’s the case in most studies of this kind, Arent says, including some he’s recently conducted in his lab.

“The reality is, both work: Both will help you gain muscle, both will help you get stronger,” he says. “But the heavier loads definitely come out with the advantage when it comes to strength.”

That doesn’t mean you always have to chase one-rep maxes, Nelson says. Powerlifters who hope to compete in a max squat, deadlift, or bench will need to train at their maximum level so they can compete that way. But if you’re not competing, you don’t have to. And for many guys, lifting that way doesn’t feel safe or fun. Shorter sets that are heavier can still give you strength gains.

“If you’re training in the five- to eight-rep range with sufficient quality and volume, they’re going to get stronger in that range—which, to me, means they’re getting stronger,” he says. “So getting stronger might mean increasing your five-rep max or your eight-rep max, not testing your one-rep max.”

Saving Time in the Gym

More Weight or More Reps: More weight

This one’s just down to math. More reps take more time, Arent says.

“This often gets lost in the interpretation of the research: If you’re doing a similar set, but you’re doing 30 reps instead of 10, the set is going to take three times as long,” he says. “So in these studies, the time investment [for low weight and high reps] is actually greater, and the results aren’t always as good.”

But don’t overthink this, Samuel says. If you’re not repping through endless, 30-rep sets, but instead choosing between sets that are five, eight, 12, or 15 reps, research has shown the work will probably take a similar amount of time. That’s because the heavier reps take a little longer to do—so five reps can take equal time as 12.

The upshot: Go heavy enough to keep yourself engaged and to keep your total workout time manageable.

To Do Big, Compound Exercises

More Weight or More Reps: Slightly more weight

Compound exercises, especially when performed with a barbell, can look impressive and usually stand in as a shorthand for strength and ability in the gym. Just think of how many times you've been asked how much you can bench press. Even as these movements are essential, you also need to approach with a plan in mind.

“One thing that I think is underrated when guys think about these joints, especially when it comes to your hips and shoulders, is that you kind of have a finite amount of reps,” Samuel says. Basically, there are only so many times in your life you can safely put your shoulders over your head, for example, before your joints start to get overused. So you should make those reps count.

“If you’re working with a lighter weight … like something that’s challenging for 12 to 15 reps … on an overhead barbell press, you’re burning through those reps faster,” he says. “So it’s almost better to stay in the five to eight rep range on your compound lifts.”

This range, he says, will let you lift safely and move the weight quickly—in addition to strength and size, increasing muscular power, which we lose rapidly as we age.

To Do Isolation Moves

More Weight or More Reps: More reps

Isolation or single-joint movements, like biceps curls and skull crushers, can be better with more reps for a few reasons, Samuel says.

For starters, lifting these movements with heavier weights in shorter sets—like the five to eight rep range—can be a “rock fest,” he notes, as lifters pitch back and forth to create momentum to cheat reps that they can't manage with perfect form.

“These moves are more about a mind-muscle connection than about strength and power,” he says. Slightly lighter weights with longer sets, like 10 to 15 reps, let you concentrate more on this connection, and get more from each set. “It’s better to be a little higher rep, and focus on the squeeze” to get the most from these moves.