Canadian researcher Stuart Phillips of McMaster University in Hamilton, Ontario, and his colleagues have been challenging the old rubric that the best way to build muscles is to lift heavy weights. Beginning in 2010, the group has researched whether lifting lighter weights for more repetitions is just as effective for building muscle as lifting heavy weights for fewer reps. Based on their newest study, the answer is yes — no matter your age or weight lifting ability.
What's crucial, the researchers say, is to push muscles until they're fatigued and can't lift any more. Whether you do that with heavy weights after a few repetitions, or lighter weights after 25 repetitions, the benefits will be the same.
"Fatigue is the great equalizer here," said Phillips, a professor in the Department of Kinesiology. "Lift to the point of [muscle] exhaustion and it doesn't matter whether the weights are heavy or light."
Their finding is especially important to older adults, Phillips added. "Why lift with heavy, joint-taxing weights when you don't have to?"
In previous studies, both heavy- and light-lifting groups had seen similar improvements in strength and muscle mass, said coauthor Robert Morton. But those studies had used only volunteers who had never lifted weights, meaning any exercise would have shown improvement. In the new study, published in the Journal of Applied Physiology, the researchers recruited 49 men who were experienced weight lifters to follow a resistance training (weight lifting) regimen four times a week for 12 weeks.
The men were divided into two groups, one that lifted lighter weights for sets ranging from 20 to 25 repetitions, and one that lifted heavy weights for eight to 12 repetitions. Both lifted to the point of muscle exhaustion.
After analyzing muscle tissue, strength and blood tests at the end of the study, the researchers found "no significant differences between groups" — meaning all the men had virtually identical gains in muscle mass and strength no matter which kind of weight they lifted.
"The point we want to get across is that you don't have to train with heavy loads," Morton said in an email. "Heavy or light, lifting weights until you are fatigued increases muscle mass and strength."
This is especially important because adults begin to lose muscle mass at age 30, and the process speeds up by age 65, especially for those who are sedentary. Exercising and resistance training can reduce the risk of age-related falls and fractures due to weakened muscles and bones.
Although they have tested both young and older men, Morton says the results should be the same for women, citing a 2005 University of Massachusetts Amherst study that found that women actually outpaced men in relative gains in muscle strength.
For women or men just starting out with weights, Morton advises going slow, using relatively light weights and the proper form for lifting. "If the goal is to increase muscle mass and strength, there is no need for women to train differently than men."
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