We have heard the standard advice: breathe out while lifting and inhale while lowering. This rule also usually comes along with artificially slow lifting, which feels abnormal as well. It turns out that those heeding this rule tend to represent proverbial weaklings that ponder more about training heavy than actually doing so.
Anyone hoisting truly heavy weights, in the gym or beyond it, knows the pattern instead looks differently. Upon initially lifting a weight or perhaps later during the toughest portion, the face visibly tenses up and the eyes widen. At this moment, the person holds their breath. They may even induce more pressure by attempting to push the air out while keeping the mouth closed. This reddens the face. This coincides with a general bracing of the body, notably the core. This occurs in daily life, and anyone that has moved big furniture realizes the truth in this description. This process occurs in bursts throughout heavy training, with breathing occurring on a sporadic schedule during less intense moments.
When you deny a natural instinct, you should question if your action feels appropriate. Listen to your body. Tendencies usually give advantages. Although holding your breath can raise blood pressure, the risk this poses to the average trainee is insignificant. Instead, the trainee that holds their breath produces a thick column of air alongside the anterior spine. This air creating pressure, along with the core muscles, enhances the stability of the spine during heavy or explosive actions. This can prevent rounding of the low back. This risk to the spine carries a much greater danger for the trainee prepared to handle heavy weights than anything cardiovascularly.
Those holding their breath for longer than necessary, especially during easier phases of the movement, are rare. The instinct to breathe kicks in eventually. Most trainees that ignore their intuition had coaching to do otherwise. Sometimes trainees ask me relentlessly about proper breathing. I find this to characterize avoidance behavior to put off hard work during a set. They instead choose to focus on some trivial element unrelated to performance. This allows them to ready an excuse for failure, should their breathing grow improper.
Do not deny the feeling to hold your breath for brief moments during heavy training. Breathe naturally and without a schedule. Doing otherwise may encourage the core muscles to relax during moments when they must remain tight. The advantage gained in spine-saving stability mitigates any temporary rise in blood pressure. Anyone facing cardiovascular issues would serve as the exception to the rule. In general, never allow minor details to bog down the real challenges you face. Hard work performed sensibly, and almost always naturally, using good exercises requires no special attention to breathing.