Breathing properly during exercise helps you to maintain a rhythm of pressing and lowering the weights. While it important to breathe steadily and not hold your breath when you are bench pressing, the breathing pattern doesn't always occur naturally. Concentrate as you inhale and exhale, following the two phases, the pressing and lowering of the barbell.
The Eccentric Phase
The bench press consists of two separate phases: the pressing movement, known as the concentric phase, and the lowering movement, known as the eccentric phase. Begin with the eccentric phase by lying on your back on a bench and holding a barbell over your chest with a slightly wider than shoulder-width, overhand grip. Start with your arms fully extended and lower the barbell to your chest by bending your elbows, allowing them to flare out to the sides. Stop the movement when the barbell touches your chest or when your upper arms are parallel to the ground. Don't let the bar bounce off your chest. You are lowering the bar with gravity; this is the easier part of a bench press.
The Concentric Phase
Pressing up is the concentric phase of the bench press. Starting with the barbell at your chest, press the weight up until your arms are fully extended. Don't bounce the weight at the top of the movement so it immediately begins to lower. Come to a full stop and pause a count before moving into the eccentric phase. You are pressing the weight up against gravity, so this is the more challenging phase of the exercise.
The American College of Sports Medicine recommends exhaling when the exercise is most challenging and inhaling when the exercise is easiest. During the bench press, the exercise is hardest during the pressing motion. Exhale as you press the weight up. The bench press is easiest during the eccentric phase. Inhale as you lower the weight back towards your chest. Perform the exercise slowly enough so you don't have to rush your breaths.
Although you should try to follow these breathing guidelines, it is more important to make sure you breathe, regardless of the breathing pattern. The Health Services department at Columbia University reports that holding your breath during exercise can result in an increase in blood pressure. This can cause you to become dizzy and light-headed, and could make you faint. This is a dangerous situation to be in if you are holding heavy weights.