Understanding Pressure and Residual Volume (RV) Depth in Freediving
When freediving, understanding the relationship between pressure and your lung capacity—specifically the residual volume (RV)—is essential for safe and successful dives. Residual volume is the amount of air remaining in your lungs after a full, forced exhalation. It represents the smallest size your lungs naturally accommodate and are adapted to.
According to Boyle's Law, "the volume of a gas is inversely proportional to the absolute pressure," which can be demonstrated by observing an air-filled balloon compressed underwater at increasing depths. As you dive deeper, the air in your lungs reacts similarly to the air in that balloon: the greater the depth, the smaller the volume of air becomes inside your lungs.
At a particular depth, this compression will reduce the volume of inhaled air in your lungs to a level approaching your residual volume. Approaching your RV can often be felt physically as an increasing pressure on your upper torso. Freedivers commonly describe this sensation vividly, using expressions such as, "RV is close when the elephant steps on your chest.
It's critically important to approach the RV-depth slowly and carefully. This depth represents a physiological boundary for comfortable and effective equalization. If you reach RV-depth too quickly or without proper control, normal equalization techniques may become ineffective, leading to what's known as "failure depth."
To safely approach your RV-depth, always avoid abrupt or jerky movements. Control your descent carefully—using the diving rope to slow down or pause if necessary—and allow your body adequate time to adapt to the increasing pressure. Progress gradually in your training, expanding your limits slowly and carefully over weeks and months to maximize safety, comfort, and performance.
Respecting the relationship between pressure, lung volume, and your residual volume is crucial in freediving. Safe progression ensures enjoyable dives and a healthier freediving experience.