In weight training, is it better to increase the number of repetitions or the amount of weight over time?
If by “better,” you mean helps you gain muscle and strength without hurting yourself, then “the answer, to me, is pretty clear,” said Stuart Phillips, a professor of kinesiology at McMaster University in Ontario, Canada. “Lighter weights!”
In a 2012 study by Dr. Phillips and colleagues, published in PLoS ONE, college-aged young men were randomly assigned to a weight training program in which they repeatedly lifted either 30 percent of the maximum weight possible for them until their muscles were exhausted; or 80 percent of their maximum until, again, their arms or legs were noodle-y. Afterward, both groups developed cellular changes related to muscle growth, meaning either routine would add similar amounts of muscle.
But lifting the lighter weights, Dr. Phillips said, also builds muscular endurance, far more so than grunting through fewer repetitions with heavy weights, and results in less risk of muscular injury. As a bonus, completing more repetitions with lighter weights also results in “a greater amount of total work” per session, meaning more calories burned than fewer repetitions with heavier weights.
The key to determining just how much you should be lifting, he continued, is gauging your point of fatigue. To become stronger and leaner, you do need to lift weights until your muscles are exhausted. If you are using the “lighter” weight approach, fatigue should set in after 15 to 20 repetitions, Dr. Phillips said. If you can’t lift a weight that many times, then, in this scenario, it’s too heavy. If you can lift it more than 20 times, the weight is or has become too light for you and it is time to add some heft.