|
Unrelated, but interesting: > That is to say there isn’t pain in the conventional sense; as CO2 goes up past critical levels, in the absence of fear or panic, the body will try breathing harder or faster and, eventually, you’ll pass out. This is why most people drown. They panic and aspire water, long before they reach critical O2 levels and pass out. It's possible to train and control the instinct to breath though. It's a great self-control exercise, and it's safe to try it outside the water. Try this: Fill your lungs and hold your breath for as much as you can. You'll notice an irresistible urge to let go and breath (this is when most people panic, even though O2 levels are not anywhere critical yet). If you ignore your brain and keep holding, you'll notice involuntary movements in your diaphragm, forcing you to breath (this is when people drown). If you still keep holding, you'll notice the diaphragm movements get more intense, up to a point when it's impossible to keep holding your breath, but it takes a while still. With enough practice, you learn to stay relaxed and post-pone those reactions as much as possible. After a while, you start being capable to hold the breath many times longer than expected. If you couple this technique with exercises for increased lung capacity and cardio (for lowering your base BPM), you'll be free-diving like a champion. |
Note that this can be dangerous while free-diving. You are essentially temporarily disabling your body's CO₂ buildup alarm thresholds, which is a proxy for too little O₂. So you need to take care to make sure that you don't run out of O₂ without noticing while under 30 feet of water, possibly while weights.
The Wikipedia page on shallow-water blackouts¹ has a nice little diagram illustrating the issue. I don't know enough about freediving and O₂ consumption to really have any clue about the margins of safety typically are, but it certainly seems like something worth understanding before messing around with too much.
¹ http://en.wikipedia.org/wiki/Shallow_water_blackout