The barbell back squat is a popular compound movement that emphasizes building the lower-body muscle groups and overall strength. It's the classic way to start a leg day, and is a worthy centerpiece to a lower-body training program. The squat is a competitive lift in the sport of powerlifting, but is also a classic measurement of lower-body strength. With the barbell racked on the traps or upper back, the emphasis is placed on the posterior chain but the entire body gets worked. The back squat can be trained in everything from heavy singles to sets of 20 reps or higher.