This idea began in the sport of bodybuilding, where competitors traditionally lifted heavy weights to put on size, then switched to lighter, higher-rep training when trying to get defined before a show. While the bodybuilders typically took this to mean that sets of 10 or more reps “burned cuts” into their muscles, the credit should really have gone to the fat-shedding diet they followed simultaneously.
True, high-rep sets do burn more calories than low-rep ones, but the difference is nominal. And research suggests that high reps are at least as effective for putting on muscle as heavy training—in fact, the Public Library of Science reported that subjects who did 24-rep sets made better gains than those who did five-rep sets. In short: Any kind of weight training can build muscle.