When weekly resistance training volume is equated, increasing training frequency leads to greater strength gains but does not result in significantly greater muscle hypertrophy.

Study: Equal-Volume Strength Training With Different Training Frequencies Induces Similar Muscle Hypertrophy and Strength Improvement in Trained Participants

If you do the same total amount of weightlifting each week but spread it over more days, you won’t get bigger muscles or stronger than if you did it in fewer sessions — your body doesn’t care how you split it up, as long as the total work is the same.

Study: Effects of training frequency on muscular strength for trained men under volume matched conditions

The study looked at whether working out more often helps build more strength when total workout volume is the same. It found no extra strength benefit, which supports the idea that doing more sessions doesn’t help much if you're already doing the same total work.

Study: The Resistance Training Dose-Response: Meta-Regressions Exploring the Effects of Weekly Volume and Frequency on Muscle Hypertrophy and Strength Gain

If you do the same total amount of weightlifting but spread it over more days per week, you’ll get stronger—but your muscles won’t get much bigger. This study found that’s exactly what happens.

Study: The Resistance Training Dose Response: Meta-Regressions Exploring the Effects of Weekly Volume and Frequency on Muscle Hypertrophy and Strength Gains.

If you do the same total amount of weightlifting each week but spread it over more days, you’ll get stronger—but your muscles won’t get much bigger. This study found that’s exactly what happens.