In untrained individuals, performing three sets per exercise does not necessarily result in greater muscle hypertrophy compared to performing a single set, when both are performed to concentric failure.

Study: Resistance Training Performed With Single and Multiple Sets Induces Similar Improvements in Muscular Strength, Muscle Mass, Muscle Quality, and IGF-1 in Older Women: A Randomized Controlled Trial.

The study found that doing one set or three sets of exercises led to similar muscle gains in older women who were new to training, as long as they went to failure. This supports the idea that more sets aren’t always better.

Study: DISSIMILAR EFFECTS OF ONE‐ AND THREE‐SET STRENGTH TRAINING ON STRENGTH AND MUSCLE MASS GAINS IN UPPER AND LOWER BODY IN UNTRAINED SUBJECTS

If you're new to lifting, doing just one hard set of an exercise can build as much muscle as three sets — at least for your arms and chest. But for legs, three sets might still be better.

Study: Pectoralis Clavicular and Sternocostal Thicknesses Increase Similarly in Response to One and Three Sets of Pec Deck Resistance Training in Untrained Young Men

The study found that doing one set or three sets of an exercise led to the same amount of muscle growth in beginners who trained to failure, so more sets didn’t help extra.

Study: Pectoralis Clavicular and Sternocostal Thicknesses Increase Similarly in Response to One and Three Sets of Pec Deck Resistance Training in Untrained Young Men

The study found that doing one set or three sets of an exercise gives similar muscle growth in beginners if they go all the way to failure, which supports the idea that more sets aren’t always better.