Fitness experts weigh in on how important weight is when it comes to strength training—plus, four other factors to focus on to ensure you’re getting the #gains you’re after.

By Jennipher Walters and Charlotte Hilton Anderson
Updated June 27, 2019
rack of dumbbels
Various weights of dumbells on a metal rack.
| Credit: Dave Bradley Photography/Getty Images

You've likely heard that when it comes to building muscle mass, heavy weights are preferred over lighter weights (and BTW, lifting heavy *won’t* create bulk—here’s what really happens when women lift heavy). And if you’re just trying to improve general muscular fitness, you’re better off doing a higher number of reps using lighter weights, right?

Well, as it turns out, what to lift when and for what purpose is a hotly debated topic in the fitness industry. But what we do know is that there’s more to the light weights versus heavy weights debate than just how heavy your weight is. The key: working the muscle to total failure or exhaustion, says Michele Olson, Ph.D., a senior clinical professor at Huntingdon College in Montgomery, AL. “If you work your muscles on each set until you cannot execute another repetition with appropriate form, the heaviness of the weight becomes less important.” (Related: 11 Major Health and Fitness Benefits of Lifting Weights)

Take one study published in the Journal of Applied Physiology. It found that regardless of how heavy people lifted, they increased strength and decreased body fat in similar amounts when they lifted to near failure. Of course, this concept of working to total failure—regardless of how much weight you're lifting—is not new, adds Olson. The American College of Sports Medicine has been recommending this strategy since the 80s and has been advising that people lift a weight that will cause exhaustion within 12 to 15 repetitions. (Also: here’s how often you should do heavy weight lifting workouts).

But does this mean the light weights versus heavy weights debate is settled? Not necessarily. "Everything matters: Sets, reps, tempo, rest, and exercise selection will all determine what kind of results you get from your weight lifting," says Lawrence Betz, C.S.C.S., director of the Brooklyn Athletic Club. So what *other* factors should you keep in mind (instead of hyper-focusing on light weights versus heavy weights?) We'll allow the experts to explain.

Know What Heavy Enough Feels Like

As a general rule of thumb, if you're using adequate load during an exercise, ideally, the last one or two repetitions of a set should feel *seriously* challenging to complete with proper form, says Jessica Matthews, director of Integrative Health Coaching within the Centers for Integrative Health at the UC San Diego.

Reconsider What “Light” Weight Means

Most women probably need to reconsider what they consider "light," Olson says. For the average 145-pound woman, a maximal squat is about 130 to 135 pounds. Therefore, lifting a "light" amount in this study would equate to doing about 25 to 30 reps holding 15- to 20-pound dumbbells. "Most women consider a dumbbell of about 10 pounds to be heavy," she says.

Focus On Volume

"The general consensus has always been that volume (how often you lift and how many reps you do) is the most important factor in seeing results from lifting weights," explains Dan Roberts, a celebrity strength and conditioning coach, trainer, and creator of the online fitness plan Methodology X. "No one thinks you need to lift incredibly heavy weights to get stronger."

So rather than focusing on lifting heavy, he says it's more important to focus on lifting enough. For example, back squatting as heavy a weight as you can handle for one rep isn't going to make you much stronger. Lightening your load a bit to something you can do for 8 to 12 reps will help you a lot more. Add in two more sets a couple of times a week and you'll start getting seriously stronger. In the end, you're decreasing the load and increasing volume so you can train your muscles to do more—it's all a trade-off between weight and volume.

Keep an Eye On Your Form

How you're actually *lifting* the weights (instead of debating light weights versus heavy weights) is also important, says Betz. Make sure you're not trying to lift so heavy that you have bad form. (Need some help? Make sure you know how to properly do a lunge, squat, or reverse fly before diving in.) No matter how heavy you’re lifting, include appropriate rest periods, too, otherwise, you're just headed for added injury instead of added muscle. Ouch.