High-volume resistance training (4 sets to failure) induces a significant increase in muscle hypertrophy as measured by ultrasound (∼0.23 cm), whereas 1-repetition maximum training does not, despite producing similar gains in strength, demonstrating that muscle growth and strength improvements can be dissociated under these training conditions.

When muscles are worked with many repetitions until exhaustion, the buildup of metabolic byproducts and sustained tension triggers signals that tell muscle cells to build more protein, making them thicker. When muscles are worked with very heavy weights for just one repetition, the tension is high but the metabolic stress is low, so the signal to build more protein is weaker, even though the muscle still learns to use its existing fibers more powerfully.