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The question

I'm not comfortable lifting heavy weights. How light can I go and still build muscle?

The answer

For once, scientific studies, decades of practical experience in the gym and logic all agree: You need to lift reasonably heavy weights to gain strength and muscle. The American College of Sports Medicine recommends 60 to 70 per cent of your "one-repetition maximum," or 1RM (the most you can lift for a given exercise), for novices, and 80 to 100 per cent for experts.

So recently published results from McMaster University in Hamilton, which suggest you can build muscle just as well - or perhaps even better - with weights as light as 30-per-cent 1RM, have been, to put it mildly, greeted with surprise.

"There are plenty of people who just don't believe it," admits kinesiology professor Stuart Phillips, the senior author of the paper, which appeared in the journal PLoS ONE.

There is a catch, however. The key to stimulating muscle growth, Dr. Phillips believes, isn't linked to any particular weight or number of repetitions - it's reaching the point of failure, where you can't lift any more.

The study put 15 active volunteers through three types of leg workouts. One group did four sets of leg extensions at 90-per-cent 1RM until they reached failure, averaging five repetitions per set. A second group lifted at 30-per-cent 1RM, with the weight chosen so the total amount of weight lifted in each set would equal the first group, averaging 14 reps per set. The third group also lifted at 30-per-cent 1RM, but lifted to failure, averaging 24 reps per set.

Dr. Phillips and his colleagues, led by PhD student Nicholas Burd, performed a series of blood tests and muscle biopsies before and after the workouts to measure the rate of muscle-protein synthesis - essentially, how quickly new muscle was growing at the molecular level.

The results were clear: The two groups that lifted to failure had roughly similar rates of muscle-protein synthesis, and both were higher than the group that didn't lift to failure. In fact, 24 hours later, the rate of synthesis for one type of muscle protein was significantly higher in the light-weights group than the heavy-weights group.

Higher protein synthesis is not the same as bigger biceps, however. Dr. Phillips hopes these initial conclusions will be confirmed by the results of a full-scale training study, in which volunteers lifted light or heavy weights and had their muscle and strength gains measured over time. The results of that study are currently being analyzed.

This new training paradigm could be important for many groups: older adults, people recovering from injuries or illness, as well as anyone who's intimidated by going to the gym, since lighter weights are more easily deployed at home.

"It's a very generally applicable mechanism," Dr. Phillips says. "And I think it's easier for most people to swallow."

It's not just a question of comfort. As you get older, your joints become more susceptible to injury and your capacity to heal connective tissue, tendons and ligaments decreases. A lifting program based on lighter weights could allow people to fight age-related muscle loss without the injury risk associated with heavier weights.

Of course, lifting to "failure" isn't easy, whether the weight is heavy or light. Fortunately, while reaching failure may be necessary to squeeze the absolute maximum out of your workout, you can probably get most of the benefits just by coming close.

"It should be a hard effort," Dr. Phillips says. "At the end, if you'd score it an eight or nine out of 10, then we honestly believe you're going to get the adaptation."

There's nothing magic about the 30-per-cent 1RM weight, he adds. Pick any weight that you're comfortable with, and if you reach (or approach) failure in 10 or 20 or 30 reps, it doesn't matter. (If it takes 100 reps, though, you should probably be a bit more ambitious.)

As with any radical break with conventional wisdom, Dr. Phillips understands the skepticism - and he's not expecting bulked-up bodybuilders to suddenly change their routines.

"We're not targeting it at them," he says. "We're just saying that heavy loads aren't the only way to induce muscle growth."

Alex Hutchinson blogs about research on exercise at