自由潜水：挑战人类极限的极端运动

The practice of freediving is teaching physiologists how humans stretch their physical and mental limits By Elizabeth Pennisi Illustration by Xiao Hua Yang An extreme endeavor Competitive freedivers push the body well beyond what was once thought humanly possible. At a depth of 70 meters, water pressure shrinks the lungs to about the size of a soda bottle. Blood oozes into the thorax, which caves in, leaving skin flapping around the rib cage. Go deeper, and blood leaving the brain resembles black sludge because it contains so little oxygen. Yet freedivers usually return to the surface, no harm done, and as such have been “rewriting the medical textbooks,” says physiologist Damian Bailey of the University of South Wales in Pontypridd. …