Anytime you perform an exercise that requires you to exert yourself, such as a pushup or pullup, it is important that you implement proper breathing. In simple terms, proper breathing is breathing in a rhythmic fashion where you always exhale as you exert force. Breathing improperly or erratically while doing pullups, or any other type of exercise, can lead to lots of negative side effects such as hernias, popped blood vessels and dramatic spikes in blood pressure.
Start from a dead-hang position with your arms fully extended and your feet off the ground.
Take a big breath, inhaling to fill your lungs.
Exhale as you begin to pull yourself up. Continue exhaling until your chin is above the bar.
Inhale a big breath as you lower yourself back down until your arms are almost fully extended again.
Exhale to complete another pullup.
Repeat these alternating, coordinated breaths as you raise and lower your body during pullups.