Figure 2.

Individual continuous recordings from Diver 1 of arterial oxygen saturation (SpO₂), heart rate (HR), and depth during immersion before starting to dive, during the shallow and the deep dive followed by a recovery period. The interruptions represent about 5 min of cut out data. The typical phases of a deep dive are indicated. In a deep dive, i.e., when lungs are compressed below residual volume which for most individuals occurs at greater depth than 30 m, four distinct phases can be identified; (1) a phase of active swimming against positive buoyancy, (2) a passive “free fall” phase when the diver can relax and fall as a result of negative buoyancy, which is after the turn followed by (3) a phase of intense swimming, when the diver actively swims upward against negative buoyancy and (4) the last phase of the dive, when swimming is aided by positive buoyancy.