I do IF when I'm cutting calories, i.e. losing muscle. Never Tried it while trying to build muscle. I practice full 24 to 30 hour fasting periodically, and did a couple 18+ recently when cutting. i really like IF especially for me cause a cup of coffee will get me through til the evening. I try to get something in me before working out, then I stack on the calories afterwards usually over about 6 hours.