The urge to breathe is strongly influenced by CO₂
During apnea, carbon dioxide rises and contributes to the urge to breathe. The first strong urge does not automatically mean oxygen is critically low, but it also does not tell you exactly how much oxygen remains. This is why training should develop awareness without turning sensations into a competition.
Relaxation changes oxygen demand
Muscular tension costs oxygen. So does unnecessary movement. Freedivers improve efficiency by reducing work that does not contribute to the dive and by learning to stay mentally quiet as discomfort increases.
Contractions are information
Diaphragm contractions are a normal part of many breath-holds. Experienced freedivers learn how their own contractions develop without assuming that a certain number or intensity is a universal safety marker.
CO₂ tolerance versus oxygen tolerance
These ideas are often discussed separately, but they interact. CO₂-focused work changes how a diver experiences respiratory discomfort; oxygen-focused work concerns performance as oxygen availability falls. Neither should be trained recklessly or used to justify unsupervised maximum attempts.
Dry training, pool training and depth are different
A dry static hold removes many environmental variables. Pool dynamics add movement and technique. Depth adds pressure, equalization, changing buoyancy and the psychological effect of descent. Progress in one context does not automatically transfer perfectly to another.
Measure quality, not only seconds
Useful training markers include how relaxed the start felt, when unnecessary tension appeared, whether technique stayed clean, how the recovery felt and whether the session could be repeated safely. A personal best is only one data point.