The most basic concern before and during the lifts in any movement you ever do will be to establish and maintain maximum body control and tension, resulting in a safe exercise and a great amount of force production. Force is important because, simply put, the more force you produce, the stronger and faster you are. And if you are lifting weights, strength and speed is always important. Control and tension will keep your joints, tendons and ligaments, and spine safer throughout the process. Now, force can only be maximized if the efforts from your base, or legs, is transferred to the bar or weight that you are using. Control, tension, and torque make this possible. And what makes control, tension, and torque possible? Proper breathing techniques.
Control and Tension is Key
What is the goal of the day? Are you lifting maximal weight for low repetitions, or lighter weight for high repetitions? In heavy lifts of one to three repetitions, you will want to take a big breath into your diaphragm, not into your chest, and hold it until the very last portion of the lift. Now, if you try to exhale from your stomach while keeping your airway closed, you create great intra-abdominal pressure. This pressure keeps the tension in your torso to protect your spine and increase force transfer throughout the lift. In lighter, high repetition sets, your breathing depends on the volume -- the number of reps being done -- and the metabolic demand of the workout. Typically, you will want to breathe deep and hold until the upward acceleration, or concentric, portion of the lift, where you let the air out in a controlled manner, then repeat each rep.
Breathing for Tension and Control
The act of breathing is only possible with sub-maximal tension in the core of your body, with the core being, for the sake of argument, everything from your glutes up to your neck. Picture absorbing a blow to your abdomen, from a punch, a kick, a baseball, anything. Would you rather be flexed and ready, or caught off-guard mid-conversation? Unless you are a glutton for punishment, you would answer "flexed and ready." So while flexed and ready, you would not be breathing. While in a conversation, you are breathing freely, and the result is, you are not in a prepared state for impact or stress. A lift is a form of impact and stress on your body, so treat it with the same respect.
Whether you are doing a heavy set or a lighter set, you will want to fill your "belly" with air, by breathing into your diaphragm, and tighten your “core” around that air. This will insulate your spine, which is crucial for safety, and create a more direct transfer of force from your feet to your head, or hands, depending on the movement. Holding the air until the last portion of each lift will ensure that you stay tight. If you release air too quickly or too soon, you risk losing that tension -- that tight, safe core that you worked so hard to establish -- and ultimately, you risk injury. So, breathe into your belly, pull up your pelvic floor, and use that ball of air to stabilize your spine and produce as much force into the movement as possible for the entire set.
Breathing During Metabolic Workouts
A metabolic workout would be a style of training that puts you in a cardio-respiratory struggle with no easing up until the end. If you are in a metabolic workout that includes weight lifting, where the purpose for the day is to do a high number of repetitions with a relatively light weight as fast as possible, you will breathe as needed. Because trying to control every breath as you would in heavier sets will leave you desperate for air, and your performance will struggle. Knowing that staying tight is crucial to your safety, breathe as needed while keeping as much tension in your core as possible to complete the purpose of the workout.