Research suggests that you need to follow certain criteria to gain muscle with aerobic activity. According to the 2014 study published Exercise and Sport Sciences Reviews mentioned above, you should aim to work out 30–45 minutes, four to five days a week to achieve enough high-volume, low-load muscle contractions to be comparable to a traditional strength-training workout. Most importantly, though, it's best to listen to your body and take the time you need to safely achieve your goals—and enjoy the process.