Lighter weights may be just as good for growing muscles as heavy weights, according to a study in the International Journal of Clinical Medicine. For six weeks, research subjects performed three 10-rep sets of the bench press using 75% of their one-rep max (1RM). Then, for another six weeks, they did four sets to failure using just 30%. The result? Subjects gained similar muscle with the heavy and light loads, indicating that size gains may depend more on taking sets to failure than on jacking up the weight.