Substantial research has supported using musical stimuli as an ergogenic aid before and during various forms of exercise. Researchers have demonstrated that music shifts attention from associative to dissociative, decreases perceived effort and discomfort, and increases arousal and pleasantness in longer-duration, low-to-moderate-intensity exercises. Strength training is shorter in duration and higher in intensity than aerobic or muscular endurance training. Limited research has examined the effects of music on strength performance and psychological outcomes. Therefore, the purpose of this study was to investigate the effects of the tempo of self-selected music on isokinetic knee extension and flexion performance, effort, discomfort, attention, arousal, and pleasantness in resistance-trained young adults. Thirty resistance-trained college-aged adults completed three exercise testing sessions. In a randomized, counterbalanced order, a repeated measures design was used to expose the participants to three conditions (fast music, slow music, and no music). The Biodex isokinetic dynamometer and standardized psychological Likert-style scales were used to measure concentric maximum effort knee extension and flexion torque at 60°/s and psychological variables, respectively. This study found that music improves knee extension torque but not knee flexion in resistance-trained young adults. In addition, music or the tempo of music did not influence any psychological outcomes during isokinetic strength testing. Therefore, listening to music is not detrimental to performance or psychological outcomes, but this study provides minimal support for music's use as an ergogenic aid during strengthening exercise.