A little muscle tone is a good thing, and based on new research it looks like lighter weights can help you achieve that goal. A new study, conducted at Canada's McMaster University, found that it's not the size of the weights that matter but rather fatiguing the muscle. To work your muscle to the magic exhaustion point to stimulate your muscle growth, you can either lift heavier weights for fewer reps or lighter weights for more reps; as long as you reach "muscle fatigue" you will be building muscle fibers.
McMaster's associate professor of kinesiology Stuart Phillips explained the process to Science Daily:
"Rather than grunting and straining to lift heavy weights, you can grab something much lighter but you have to lift it until you can't lift it anymore. We're convinced that growing muscle means stimulating your muscle to make new muscle proteins, a process in the body that over time accumulates into bigger muscles."
This is good news for a variety of reasons. While working with heavy weights can make you feel like a super toughie, they can be hard on your joints. Creating joint pain is not what you want out of a strength training session. Plus, lighter weights are less intimidating, so if you're not ready for 20-pound dumbbells no worries. Just be sure to do enough reps to thoroughly exhaust the muscle.