I took a breath-hold diving course with the people who were working with David Blaine last night, a group called PERFORMANCE FREE DIVING.
They are competitive breath-hold divers. The owner Mandy Cruikshank is a womens champion and has held her breath for seven minutes, I forget how deep she dived one one breath, but I believe around 300 feet. One of the instructors, Martin Stepanek, is a men's champion and has held his breath for over 8 minutes and has also dived to 300 feet on one breath.
It is a competitive sport which requires lots of training. In the course I took, by the end of it, I could hold my breath for over three minutes, and my deepest dive on one breath was to 70 feet. And I was the WORST one in the class! The other students were much younger, and some of them work in the water every day. They were diving to over 100 feet on one breath, and staying down 4-6 minutes. It was amazing!