3 Balls Spirometer Respiratory Lung Exerciser works on the principle of resistance. As you inhale, the resistance created makes your respiratory muscles work harder, and the harder they work the stronger and more durable they become. As your breathing power improves, 3 Balls Spirometer Respiratory Lung Exerciser can be gradually adjusted to provide more resistance with just the twist of a knob. It can even help reduce the feeling of breathlessness from some lung diseases such as asthma, bronchitis and emphysema. Doctors have been prescribing big, bulky breathing devices for post-surgery patients to increase their lung power for years. 3 Balls Spirometer Respiratory Lung Exerciser gives you the same effects, but is so small and compact you can take it with you to exercise your lungs wherever you are. Whether you are exercising for cardio fitness, sports or not at all, you will breathe deeper and more easily than ever. Within a month you will feel the wonderful effects of strong, healthy lungs.