Also Quasi,
If you intend to train to freedive, a thorough understanding of dive physiology is very important. I don't know if you have attended a freediving class or not. I went to a class offered by
www.performancefreediving.com that was quite thorough. The discussion included physiology of freediving as well as general training techniques and a training program. I am glad that I took the class before I spent any time trying to deep swim. I never could have been as effective without the advanced instruction from Martin Stepanek and Kirk Krack.....
The basics included flexibility training and breathing exercises with a focus on ribcage flexing. Also there are static apnea tables that are very easy to understand as well as physical training in techniques like packing, proper dive form and many other important topics. There were also recommendations regarding dynamic apnea practice like breathing up, holding one's breath and walking as far as possible (preferably in a grassy park)...
I think the most important info was in respect to initiating the mammalian diving reflex through a sequential series of exercises begining with stretching and ending with negative pressure submersions just prior to breathups for deep dives.... there are a series of physical cues that tell your body to prepare for prolonged submersion and learning how to stimulate these cues in the proper order is probably one of the most important aspects of learning to freedive. I can certainly tell when I have prepared correctly prior to diving.
One other important aspect beyond a proper and effective breathup is the simple practice of relaxing, minimizing the use of large muscle groups(dolphin vs flutter kick), taking one's time on descents, engaging the sinkphase effectively, etc... I like to do a dive, make the majority of my ascent and if I am comfortable, I will slow down my ascent and let my positive bouyancy take over.... I am relaxed, low on 02 but not completely drained, and I can simply relax and make it go a little longer.
I often dive in small bays like Kealekakua or H'nau Nau. I will spend two or three hours, sometimes much longer, simply diving and breathing up. Start with shallow dives after a correct warm up and then work out from shore to deeper water. I might do 50 dives in a session, even more if I am motivated. I just concentrate on relaxing, getting into negative bouyancy with minimal effort, and the rest is simply a matter of really thinking about what I am doing while I am doing it.... I try to do this every other day as it can take that long to heal up diaphragm, intercostal and subclavials...
