If you're a young man who already lifts weights, doing workouts with either light weights (lots of reps) or heavy weights (fewer reps)—as long as you push yourself until you can't do another rep—will make your muscles grow just as much either way.

A 12-week RCT with resistance-trained young men randomly assigned to either low-load (30–50% 1RM, 20–25 reps/set) or high-load (75–90% 1RM, 8–12 reps/set) resistance training, both performed to volitional failure, with muscle biopsies taken pre- and post-intervention to measure type I and type II fiber cross-sectional area as the primary outcome.

A 12-week within-subject crossover RCT where each resistance-trained young man completes two 6-week blocks of training—one with low-load and one with high-load—both to volitional failure, separated by a washout period, with muscle biopsies taken after each block to compare fiber hypertrophy directly within individuals.

A prospective cohort study tracking resistance-trained young men over 12 weeks who self-select into either low-load or high-load training groups (both to failure), with pre- and post-intervention muscle biopsies to compare fiber hypertrophy, controlling for volume, frequency, and diet.

A systematic review and meta-analysis pooling data from all published RCTs comparing low-load vs. high-load resistance training to failure in resistance-trained young men, with muscle biopsy-derived fiber CSA as the primary outcome.

A case series of 10–15 resistance-trained young men undergoing 12 weeks of either low-load or high-load training to failure, with detailed pre- and post-intervention muscle biopsies and imaging to assess fiber-specific hypertrophy.