5/3/1 is a popular bodybuilding program developed by Jim Wendler, a former powerlifter and coach. The program is designed to improve strength and build muscle by focusing on the four main lifts: squat, bench press, deadlift, and overhead press. The 5/3/1 program is structured around a four-week cycle, where the focus is on a specific lift each week. The first week consists of performing sets of 5 reps, the second week of sets of 3 reps, and the third week of sets of 1 rep. The fourth week is a deload week, where the weight is reduced to allow for recovery and preparation for the next cycle. In addition to the main lifts, the program includes accessory exercises that target specific muscle groups to help build overall strength and size. The accessory exercises are chosen based on the individual's goals and weaknesses. The 5/3/1 program is a flexible and customizable approach to bodybuilding, allowing for adjustments based on the individual's needs and goals. It is a popular program among strength athletes and bodybuilders due to its effectiveness and simplicity.