Can You Build Muscle by Lifting Light Weights?

If you’ve ever watched powerlifters training, you’ll see they lift heavy weights. In fact, the weights they train with are so heavy they can only do a few repetitions before their muscle fatigue and they have to stop. The method they’re using, heavy weight and low repetitions, works well for maximizing strength gains. That’s because lifting very heavy weights maximally recruits fast-twitch muscle fibers, the fibers best suited for generating force.

Bodybuilders, in contrast, use weights that are a bit lighter and do higher repetitions, usually in the 8 to 10 repetition range, before their muscles fatigue. Research suggests that moderate weight and higher volume is a better formula for muscle hypertrophy or building new muscle. When you build new muscle tissue, your muscles increase in size and look more defined.

Why the discrepancy?

Powerlifters and bodybuilders have different objectives. The former wants to maximize strength gains while bodybuilders focus more on aesthetics, like having good muscle definition. But what if you lift lighter weights, weights that are so light you can do 20 or more repetitions? Older research suggests that lighter weights increase muscle endurance, but can they build muscle size too?

What Study Shows about Muscle Hypertrophy and Lifting Lighter Weights

Researchers at McMaster University put lighter lifting to the test. They divided healthy, experienced weight trainers into two groups. The first group lifted heavy weights, equivalent to 90% of their one-rep max, the maximum amount of weight an individual can lift for one repetition.  One-rep max is a rough measure of a person’s strength. So, these guys were lifting heavy. The second group lifted weights that were 50% of their one-rep max. Because the first group worked with heavier weights, they were limited in the number of repetitions they could do and performed 8 to 12 repetitions. The second group was able to complete 20 to 25 repetitions before fatigue set in.

The exercises they did were compound exercises that worked multiple muscle groups and they did the exercises until their muscles reached failure, the point where they couldn’t complete another repetition using good form. After 12 weeks, researchers compared their muscle gains.

Were there differences in muscle development between the heavy and light lifters? To see, they checked markers of muscle protein synthesis in the blood and did a muscle biopsy to see how their muscles had changed. Despite the differences in the weight they used and the repetitions, both groups gained similar amounts of muscle.

Another study published in the Journal of Applied Physiology came to similar conclusions. In this study, two groups of men did leg exercises using a resistance equivalent to 80% of their one-rep max. Both did 3 sets of leg exercises but one trained to muscle fatigue while the second trained to muscle failure, where it was impossible to complete another repetition. A third group did 3 sets but used a resistance equivalent to 30% of their one-rep max, much lighter and trained to muscle fatigue. The results? All three groups enjoyed similar gains in muscle.

What This Means for Building Muscle?

You can build muscle size lifting weights as long as you lift until your muscles are thoroughly fatigued or close to muscle failure. It’s not a good idea to take every set to complete muscle failure, as this requires more recovery time and places too much stress on your muscles. So, if you don’t enjoy lifting heavy, you can still increase the size of your muscles using lighter weights. The key to success is working the muscles to fatigue. Your muscles should feel spent by the end of each set.

Although lighter lifting works for building muscle size, it’s not as effective for increasing muscle strength. Beyond the early stages of strength building, where you can make gains with lighter weights, you need heavy weights to maximize strength gains but the same isn’t true for muscle hypertrophy. In fact, higher volume and more repetitions, up to a point, is favorable for hypertrophy gains.

Regardless of how much you lift, you have to increase the challenge over time by increasing the resistance once a set becomes easy at the current weight. Another option is to increase the number of reps or do more sets. With this method, you increase total training volume, so your muscles have to work harder There are other ways to increase progressive overload too. Don’t let your training become stagnant.

The Bottom Line

You don’t have to lift heavy to increase muscle size but lifting lighter weights will limit your strength gains. The key to building muscle size with lighter weights is to fatigue your muscles. No cheating!

References: “Lighter Weight Just as Effective as Heavier Weights to Gain Muscle, Build Strength”

  1. Neurophysiol. 90, 2919-2927 (2003).

Brett Contreras. The Glute Guy. “March Research Round-Up: the Muscle Fiber Types Edition”





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