Gaining strength is about how hard you work, not how much you lift.
If you're looking to build muscle but worry about overdoing it with the barbells, here is some encouraging news: Research shows that contrary to popular belief, lifting lighter weights for more reps can be just as effective as lifting heavier weights for fewer reps.
For the study, published in the Journal of Applied Physiology, researchers from McMaster University followed 49 young men over the course of a 12-week, full-body resistance training program. About half the participants used lighter weights for sets ranging from 20 to 25 repetitions. (Each person's weights were set at 30% to 50% of his one-repetition maximum, or the amount he could lift one time.) The other half lifted heavier weights (set at 75% to 90% of each man's one-rep max) for sets ranging from 8 to 12 reps. Both groups worked until the point of fatigue.
What the researchers found: The gains in muscular strength and size among participants in the first and second groups were not significantly different.
"This research is significant because it challenges current resistance exercise dogma and guidelines," says study author Robert W. Morton, a PhD candidate at McMaster University. "Put simply, your effort is more important than the weight you use."
Ideally, he says, the findings will motivate more people to take up resistance exercise, "particularly those who may have been intimidated by the need to train with heavy weights," he says.
So go ahead and grab whatever set of dumbbells you please—as long as you keep up the reps until you can't do any more.