I've got a confession to make. Many people believe that lifting weights is the key to build muscle mass. This can't be further from the truth. In fact, muscle building can be done through what is known as resistance training. It doesn't matter whether you're lifting weights or performing bodyweight exercises, the most important thing here is that you're using your muscles to overcome a resistance force. Exercises like push-ups, pull-ups, chin-ups, dips, bodyweight squats are sure-fire ways you can build muscle mass without ever touching weights. These are actually known as calisthenics and they should be the foundation of any workout routine. Frankly I consider weights only to advance my training after I have properly mastered bodyweight training which can hit a plateau with time. Here are 5 calisthenics you can perform to build muscle mass:

Push-Ups: Many times when you hear push-ups, you tend to think of military guys performing push-ups daily. The truth is push-ups are one of the most popular exercises in the army and can really build great muscle mass if you perform them regularly with intensity like doing several sets. Push-ups target primarily the chest muscles(pectorals) and to some extent the triceps and shoulders. The standard push-up is the most common but there are several variations of push-ups notably declined push-ups(working mostly upper chest), push-ups between chairs(outer chest), handstand push-ups(lay emphasis on triceps and shoulders), diamond push-ups(mostly triceps and inner chest) and declined diamond push-ups(laying more emphasis on triceps and shoulders). Here is a sample routine:

Declined push-ups - 3 sets of 8-15
Push-ups between chairs - 3 sets of 8-10
Diamond push-ups - 3 sets of 8-10

45 seconds rest between sets and 2 minutes rest between exercise.

Pull-Ups: Same as with push-ups, pull-ups are popular calisthenic exercises in the military. In fact both of them go hand in hand. Pull-ups target primarily the back muscles including the lats, the middle back(rhomboids), the traps and to some extent the biceps, forearms and shoulders. Pull-ups are actually very tough to perform initially as you'll need enough strength in your arms to be able to raise your body up to the pull-up bar. Performing negative pull-ups can actually help novices in building strength. What you need to do is grab the pull-up bar and try to lower your body slowly in a controlled fashion. Of course you need to bring your body initially to the bar then lower gradually. You might need a chair to assist you if the bar is too high up. Negative pull-ups are a great way to strengthen your arms and give you a kickstart to your pull-up routine. Wide-grip pull-ups use a pronated grip(palms facing away from you) and target mostly the upper lats and to some extent the traps, biceps, forearms and rear shoulders. If you want that V-Taper body, start doing wide-grip pull-ups. Once you reach 2-3 sets of 8-10 repeats, you can build muscle mass more effectively because performing only a couple of pull-ups is not enough to develop your back. Close-grip pull-ups can also be done and these target mostly the lower lats and rhomboids as well as the secondary muscle groups like biceps, forearms, shoulders. Close-grip pull-ups also use a pronated grip.

Chin-Ups: Same like close-grip pull-ups but this time using a supinated grip(palms facing you), chin-ups also build lower lats, rhomboids and several other secondary muscle groups but this exercise lays a strong resistance on your biceps. A pull-up bar can be easily installed in your home and it's best if you can fit it between two concrete walls.

Dips: The best way to perform dips is to use a dip station like what you have at the gym but if you don't have access to a dip station, chairs can also be used as an alternative but be sure to have 2 sturdy chairs with high backrest so that your body can be elevated. Dips can also be as hard as pull-ups and the main muscle groups worked are chest, triceps and shoulders. If you lean your body forward, you target more the lower chest but if you keep your body straight, more emphasis is laid on triceps. Lower your body till your elbows reach a 90 degree angle and back to initial position. You can also use another technique to perform dips and you will also need two chairs here but used differently. Place both arms behind your back on a square chair and your legs on another chair.

Bodyweight Squats: Squats are powerful leg builders and you don't need heavy weights to perform squats. Try your own bodyweight and perform 4-6 sets of 25 repeats and your quads will be on fire. Always keep your back straight and legs spaced apart about 1 feet and perform the squats in a controlled manner with no jerking motion. Squats work the quadriceps, hamstrings, glutes and calves.

The great thing about these calisthenic exercises is they are all compound exercises, meaning you can have a total body workout with just 5 exercises since they work so many different muscle groups. If you really want to grow your muscles fast, this is where you should focus your efforts on. Master calisthenics and once you reach a plateau, you can add weight training alongside them.

If you want to specialize in calisthenics, I highly recommend you to check out Complete Calisthenics: The Ultimate Guide to Bodyweight Training by Ashley Kalym.

Complete Calisthenics: The Ultimate Guide to Bodyweight Training