“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,” says Stuart Phillips, associate professor of kinesiology at McMaster University. “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.”
The heavier weights were set to 90% of a person’s best lift and the light weights at a mere 30% of what people could lift. “It’s a very light weight,” says Phillips noting that the 90-80% range is usually something people can lift from 5-10 times before fatigue sets in. At 30%, Burd reported that subjects could lift that weight at least 24 times before they felt fatigue.
source : psyorg