Lighter weights do as much for building muscle as heavier ones, new research says

Size doesn’t matter.
Size doesn’t matter.
Image: AP Photo/Alastair Grant
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When it comes to building muscle, it’s probably not the size of your weights or the number of repetitions that matter.

Research (pdf) from McMaster University in Ontario, Canada argues it’s actually the degree to which you exhaust yourself during your weightlifting session.

“It isn’t about the weight that you lift, but instead it’s about how much effort you’re putting in,” Robert Morton, a graduate student in kinesiology at McMaster University and lead author of the study, said.

For their work, Morton, who is also a weightlifting coach, and co-author Sara Oikawa worked with 49 men who had been lifting weights for at least two years. The men were divided into two groups: One lifted lighter weights with 20 to 30 repetitions, and the other used heavier weights for eight to 12 repetitions. Participants pushed themselves to lift until they couldn’t complete another repetition, and had a minute break in between sets. They met for full-body training four times a week, and didn’t do any outside exercise. At the end of three months, researchers found that both groups’ muscles (the thigh, which was tested) developed to a similar extent.

Morton and Oikawa trained each participant individually. ”We were the ones, who, every single set, made sure that they were spent,” Morton said. If the coaches saw that participants could do another rep of an exercise in either group, they would force them to do so—and would increase the weight slightly on next set.

The team also sampled participants’ blood. They found that before and after workouts, all of the men had similar amounts of testosterone and growth hormones, suggesting that adding muscle is unrelated to different hormone levels.

Although this was a relatively small study, Morton is confident that these results could translate into anyone looking to put on muscle. This study is the latest in a line of work challenging the conventional idea that building muscle requires lifting heavy weights. Preliminary work published by the same research group in 2010 showed that lifting lighter weight with more repetitions could actually help build muscle better than heavier weights at low reps. In 2012, the same group showed that men without previous training could also develop muscles using either strength training regime, provided they exercise until they’re totally exhausted.

“If you exercise until you’re completely wiped, you’re going to be in good shape,” Morton said.