Context: Strength/resistance training volume has historically been supported in the American College of Sports Medicine recommendations. However, for the back muscles, exercise prescription related to the number of sets, such as single versus multiple, is not well established in the literature. Objective: The purpose of this study was to compare the effects of 2 training volumes on strength and endurance of back-extensor muscles in untrained young participants with regard to a repeated-measures design. Design: Randomized controlled trial. Setting: Laboratory of functional evaluation and human motor performance. Participants: Forty-four untrained young participants (mean age = 21 y) were randomized into single-set (n = 14), multiple-set (MSG, n = 15), and untrained control (n = 15) groups. Intervention: The single-set group and MSG underwent a 10-week progressive resistance training program (2 d/wk) using a 45° Roman chair. Main Outcome Measures: Back maximal strength (dynamometer) and isometric and dynamic endurance (time limit, trunk extension–flexion cycles, and electromyography muscle fatigue estimates). Results: The results showed differences between the MSG and control group for isometric endurance time (mean = 19.8 s; 95% confidence interval, −44.1 to 4.8), but without time intervention significance. Significant improvement after training (P < .05) was found predominantly during dynamic endurance (number of repetitions) for both the MSG (+61%) and single-set group (+26%) compared with preintervention, whereas the control group reported no benefit. There was no significant (P > .05) difference in either strength or electromyography estimates after training. Conclusions: Both multiple and single volume training were efficient in promoting better back endurance during dynamic performance based on mechanical variables (time and number of repetitions).