People can work out arms and legs on the same day. It is advisable to avoid working the same muscles two days in a row.
Muscles need rest in order to grow stronger. Working arms and legs on the same day is fine as long as individuals remember which muscles they exercised. Many people have a designated arm and leg day to reduce the chances of working the same muscles two days in a row. To avoid repetition, the Mayo Clinic suggests working all major muscle groups two or three times per week or planning daily workouts for specific groups of muscles.