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Are lighter weights just as effective as heavier weights?

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Photo: Scott Webb/Unsplash

Isn’t it common knowledge that in order to build strength and build muscle, you need to lift increasingly heavier weights? Turns out, that might not be true. The reason? It’s all about fatigue, not weight, according to a new study.

Researchers at McMaster University in Canada found that lifting lighter weights many times is just as efficient as lifting heavier weights for fewer reps (exciting news to me).

The study began in 2010 and looked at two groups of professional weightlifting men (caveat: no women were included in the study—boo!) who followed a 12-week full-body routine—one group with heavier weights and fewer repetitions, one with lighter weights and more repetitions.

“Lift to the point of exhaustion and it doesn’t matter whether the weights are heavy or light.”

After their muscle and blood samples were analyzed, the gains in muscle mass and fiber size (key measures of strength) were essentially identical. So this means that fatigue—not weight—helps us get stronger.

“Fatigue is the great equalizer here,” says McMaster kinesiology professor Stuart Phillips, the senior author on the study. “Lift to the point of exhaustion and it doesn’t matter whether the weights are heavy or light.”

So was Tracy Anderson right in her advocacy of using lighter weights? Either way, I’ll happily continue to bypass the heavy weights section at the gym (I always pretend I don’t see weights above 7.5 pounds when an instructor tells the class to grab heavier weights) without feeling an ounce of guilt.

While you’re at the gym, make sure you’re not making these four common mistakes in terms of form. And speaking of debates: Experts weigh in on whether the machines at the gym actually do any good.