Fig. 1

Transrespiratory pressure (Ptr) [static lung load (SLL)]. A: a diver using a closed-circuit rebreather worn posteriorly in the prone position, the transpulmonary pressure gradient is negative (negative static lung load, SLL-). B(1-2-3): divers during water surface during surface fin swimming exercise, utilizing a snorkel for breathing. B-1: a diver without wearing scuba tanks. The SLL is slightly negative. B-2: a diver carrying scuba tanks. Right from the beginning of the surface exercise, the diver's torso is submerged deeper in the water, leading to a deeper negative Static Lung Load (SLL) from the onset of immersion. B-3: same diver as presented in Figure B-2 after several minutes of fin swimming. Due to fatigue, the diver gradually loses the horizontal position on the water surface and becomes less buoyant. As a result, their lower limbs start to sink, causing a tilting of the torso. This further accentuates the negative SLL value. After an hour of surface swimming, the negative SLL becomes significantly deeper compared to the beginning of the exercise