Holding your breath under load isn't a dangerous habit — it's working technique
The Valsalva maneuver — holding your breath while bracing your abs against a closed airway — often worries beginners because it's associated with raised blood pressure. And it's true: during the maneuver, both intra-abdominal and arterial pressure briefly rise. But that rise in intra-abdominal pressure creates a kind of internal 'air cushion' around the spine, meaningfully increasing its stability and its ability to handle a heavy load without excessive flexion.
Research on spinal biomechanics under load shows that using this technique on heavy squats, deadlifts, and overhead presses reduces compressive load on the spinal discs compared to breathing normally through the lift — meaning a technique that sounds risky actually protects the back more than skipping it does.
Caution is warranted for people with existing cardiovascular conditions or uncontrolled high blood pressure — they should check with a doctor before using the technique on heavy sets. For most healthy people who train, it's a standard, safe tool, not a dangerous habit to break.