Background/Aim. Exercise designed to condition the lumbar extensor musculature is often included in resistance training (RT) programs. It is suggested that deconditioning of this musculature may be linked to low back pain. Thus effective means of conditioning these muscles are of interest to pursue. Evidence suggests that isolated lumbar extension (ILEX) RT might be most efficacious, however, the best means of manipulating resistance training variables in this regard is unknown. Set volume is an easily manipulated RT variable and one thought to also interact with training status. As such this study sought to examine the effect of set volume during ILEX RT in trained males. Methods. Trained males previously engaged in exercises designed to condition the lumbar extensors underwent a 6 week intervention and were randomised to either a single set (1ST, n = 9), multiple set (3ST, n = 8) or control group (CON, n = 9). Pre- and post-testing of ILEX strength was conducted. Results. Both 1ST and 3ST significantly increased ILEX strength (p < 0.05) with large effect sizes (d = 0.89 and 0.95 respectively) whereas the CON group produced significant losses (−8.9%) with a moderate effect size (d = − 0.53). There was no statistically significant difference in ILEX strength gains when 1ST and 3ST were directly compared (p = 0.336). Conclusions. The results of this study suggest that significant ILEX strength changes occur in trained males as a result of 6 weeks of ILEX RT and that these changes are unaffected by set volume.