[ricki]

This is an intriguing video clip, you should check it out. Martin's sink phase or when he develops negative buoyancy due to weighting and normal lung compression below 20 m is impressive. In free diving much below 66 ft. you may wear a 3 mm full suit with hood but may carry only 0 to 3 lbs. of lead and still go negative. Boyles Law is a wonder. His kicking speed during ascent is surprisingly fast too. You work to develop ideal speeds of descent and ascent through extensive training. You need to balance exertion, air consumption vs. efficient travel up and down. Imagine all that negative buoyancy from compression hundreds of feet down to overcome on ascent. Martin needs a new free diving watch though, his ruptured under the pressure!