“Doing it to failure also helps you build more muscle/muscle cells.”
“However, growth in cell numbers is limited to the prenatal and immediately postnatal period, with the animals and man being born with or soon reaching their full complement of muscle cells. “
https://pubmed.ncbi.nlm.nih.gov/2222798/
Interestingly, that may not be the case:
“A novel imaging method (FIM-ID) reveals that myofibrillogenesis plays a major role in the mechanically induced growth of skeletal muscle
https://pubmed.ncbi.nlm.nih.gov/38466320/