Conventional gym wisdom has long offered a basic rule of thumb for novice and intermediate weightlifters: If you want to increase muscle size, lift relatively light weights for a lot of reps. If you want to get strong, lift heavy weights for just a few reps.
Simple, right? But a new study of relatively experienced weightlifters is challenging that old gym law.
The new findings: Lifting relatively light weights (about 50% of your one-rep max) for about 20–25 reps is just as efficient at building both strength and muscle size as lifting heavier weights (up to 90% of one-rep max) for eight to 12 reps, according to the study, the latest in a series done at McMaster University in Ontario.
"Fatigue is the great equalizer here," Stuart Phillips, Ph.D., a kinesiology professor at McMaster and the senior author of the study, wrote about the research. "Lift to the point of exhaustion and it doesn't matter whether the weights are heavy or light."
Phillips and his colleagues asked 49 men, each about 23-years-old, to do a 12-week program of total-body resistance training. The lifters were split into two groups: a high-rep group, which lifted at 30–50% of their one-rep max for 20–25 reps a set, and a low-rep group, which lifted at 75–90% of their one-rep max for 8–12 reps a set. Both groups lifted to failure, and did four exercises: inclined leg press, barbell bench press, machine-guided knee extension, and machine-guided shoulder press.
At the end of 12 weeks, the authors tested the participants’ muscle mass and found that both groups had made essentially equal gains in strength and size—except for in the bench press, which was higher among the low-rep group.
Why the equal gains? Total work volume—that is, reps times weight—is a good way to force muscle growth.
“As long as you’re doing enough volume, you’ll positively adapt to the training,” says Sean Collins, C.S.C.S., a USA Powerlifting-certified trainer and powerlifting coach at Murder of Crows Barbell Club in Brooklyn. "Volume acts as a driver that overloads the body to make an adaptation, also known as supercompensation.”
That’s good news, especially for guys who are hesitant to hit the heavy weights but still want to make gains.
“Studies like this are a wake-up call to trainers and lifters who thought you exclusively had to lift heavy—at least 75% of your max, or about 10 reps and below—to get big,” says Sean Hyson, C.S.C.S., Men’s Fitness training director. “It’s also encouraging for older, beat-up guys with joint issues and injuries. They sometimes think they can’t train hard anymore, but if they just go lighter and do more reps, they can build muscle too.”
Bottom line: “It’s the effort you put in that matters most,” Hyson says. “Lifting heavier builds more strength, but lifting to failure with any weight can build bigger, more aesthetic muscles.”
As with all single studies, it’s important not to take this one as law. We know the participants had been lifting for at least two years before the study, but we don’t know exactly what kinds of workout programs they were pursuing before taking part in the experiment.
So does this mean for the average gym-going guy? Here are five important takeaways that you should remember: