The fitness world has learned a lot over the past 20 years. Much of the prevailing wisdom from the last century has been debunked, or refined, since then. Here is a summary of the latest thinking of the best way to optimize your workouts, and your workout schedule, to maximize muscle gains.
1) Target each muscle groups twice a week. There is enormous benefit to working out each muscle group a second time each week, however there is very little additional benefit from a third workout.
2) Give each muscle group 48-72 hours to recover between workouts. For example, if you work out your biceps and back on Monday, wait until Wednesday or Thursday to work those same muscles again.
3) Take each set to failure, between 6-15 reps. If you can't do 6 reps, use less weight. If you can do more than 15 reps, use more weight. Usually try to target 8-12 reps with the goal of getting to failure at the end of each set. Techniques such as drop sets and super sets can also help you achieve failure. The growth comes in the failure!
4) Each time you exercise, try to have 8-12 sets for each muscle group. Ideally this is spread across 3-4 different exercises, because each movement will activate the muscle in slightly different ways. For example, on chest day you may do 3x10 bench press, 3x10 chest flys, 3x10 incline dumbbell chest press. That's a total of 9 sets and 90 total reps focused on your chest. Another example, on tricep day you may do 4x12 rope pressdowns, 3x10 skullcrushers, 3x12 tricep extension machine, and 4x8 tricep dips. That is a total of 14 sets and 146 reps focused on your triceps, but targeting them in slightly different ways. Bonus tip: later in the week when you are working out your triceps again, choose different exercises for even more variation.
If you employ all of these tips you will hit every muscle group twice a week with 6-8 different movements and somewhere between 150-300 reps per muscle group! To accomplish this, while also giving each muscle at least 48 hours to recover, you will likely work out 5-6 days a week. This isn't for everyone, but for those that really want to focus on growing their muscle mass, these tips can help you achieve your goal.
There are many other tips and tricks for growing your muscle mass, from diet to sleep habits, supplements to recovery techniques. We encourage you to do your homework and develop an exercise plan that works within your lifestyle while still challenging you to commit and create new, healthy habits!