Building muscle without the use of weights, also known as body weight training, can be very effective. Regardless of the equipment you use, the key is to place your muscles under tension by using resistance and progressive overload. The classic routine of body weight training includes squats, pull-ups, chin-ups, sit-ups and lunges. There are many interesting ways to expand on these basic principles and I encourage everyone to learn a little bit more about closed kinetic chain exercises (CKCE).  Regardless of which method you ultimately choose, if you stick with a brief weekly routine, the benefits can be immense and help you maintain flexibility, alertness, prevent loss of bone minerals and maintain critical muscle mass.