It’s been said that lifting weights in the range of 6 to 8 reps is ideal for building muscle. Ideally, after completing the eighth repetition, you shouldn’t be able to complete a ninth. This is what’s known as your 8 reps max (8RM). A study published in the Journal of Science and Medicine in Sports tests this theory on 28 untrained men and women in their early 20s using 4 different weight training exercises.
After becoming familiar with each of the exercises, subjects performed 2 sessions of lifting with 2 to 3 days between workouts to allow for recovery. Researchers determined that setting resistance at 8RM was a reliable way for both men and women to build muscle using a variety of different exercises. It might take a session or two to determine your 8RM. In a couple of months, when that 8th rep becomes too easy, it’ll be time to recalibrate your 8RM. Keep in mind, the amount of weight will vary from exercise to exercise.