You have probably seen someone grinding through a heavy lift with a red face and visibly trapped air in their chest, and you have probably also heard that holding your breath during a workout is dangerous. Both things seem contradictory, but they are not: there is a specific breathing technique for heavy lifts, with a name of its own — the Valsalva maneuver — and a right moment to use it. The problem is that most people never learned when it actually helps and when it is unnecessary or risky, so they end up holding their breath through the entire session, even during light warm-up sets, without really knowing why.
What happens when you hold your breath to lift heavy
The Valsalva maneuver means taking a deep breath, closing your glottis — the valve in your throat that controls airflow — and trying to exhale against that closed passage without letting any air escape. The immediate result is a spike in pressure inside your abdomen, which pushes your abdominal wall outward and creates a kind of rigid cylinder around your spine. That cylinder acts like a natural brace: it stabilizes your spine and reduces how much it has to flex or twist under load.
Source: PubMed
That is exactly why the technique shows up in the heaviest lifts — squats, deadlifts, near-max bench press — and almost never in light exercises or low-load machine work. The heavier the load relative to your max strength, the more your spine needs that extra pressure to stay stable, and the more the maneuver pays off for the effort.
Why abdominal pressure lets you lift more weight
The right way to build that pressure is not to fill up your chest with air, but to breathe into your belly: the inhale should expand your stomach forward and to the sides, not lift your shoulders. This diaphragmatic breathing produces higher intra-abdominal pressure than chest breathing does, because it uses the diaphragm together with the abdominal muscles to create a real belt of pressure around your torso.
Source: Stronger by Science