Monday, October 8, 2007

The arc of a diver

Lucia: Dive reflex not always helpful? I have been doing dry and pool {dive} training for a long time now, and my dry breath holding apnea performance is always significantly better than in the pool. I have tried to work out what the reason is, but nothing fully explains it. What a useless reflex, I don't know how it could possibly be good in any situation to gasp when falling into cold water.

DD: It helps to understand how the body reacts to temperature and pressure changes.

Feet first: gasp, wading in cool water
Face first: MDR, diving in cool water

It's actually the same reflex, maximizing oxygen retention, but face-first shuts off the inhalation phase, while feet-first exaggerates the inhalation phase.

Your best MDR response might be this approach:
(with a buddy at poolside watching and estimating time, not a small crowded pool)

1) NO wetsuit, just swim suit, warm and dry, no nose/ear plugs/mask/cap.
2) PLAN only ONE dive, (afterwards hit the hot shower, then dry and leave).
3) NO breathe up, just walk to the edge of deep end, casually deflate lungs while leaning forward, and pushing gently off into the water, entering face-first with arms down at your sides, to between 1/2 to 2 meters deep, glide down and forward until stopping, then casually but with strength, kick a few times while gliding hydrodynamically, then, when ready to climb, [*see note below] bring your arms forwards and SLOWLY power stroke laterally at sides (no more kicking) diagonally or vertically up to the surface, turn onto your back and inhale a few slow moderate breaths (not deeply) while laying flat like a board on the surface relaxing, backstoke over to the edge and climb up and leave pool. You did it. Shower, dry, go home, forget it.
4) It's not the length of time or distance, it's the technique, 20 seconds submersed is fine.
5) That night, dream the dive again, let the experience come back, learn from it subconsciously while sleeping, adjust little things (slower or faster kick, hear echoes under water, sense difference between surface temp. and depth temp. etc.).
6) Repeat pool dives often, after the first day, 2nd and 3rd dives are ok, but stay focussed on technique, hydrodynamics and sensing conditions. No more dry/wet statics until normal dives are smooth enough to make a dolphin smile.

* Assuming no lane intrusions and not close to wall, close eyes during ascent and allow face skin to inform you of your position. Your ears know the depth and body orientation via the eardrums and the 3 semicircular canals of the inner ear, your hair/forehead/eyebrows/eyelids/eyelashes know the speed and the difference between water and air temperature and pressure, rely on this sensitivity. Once in backfloating position and ready to scull to the edge, only then open the eyes and go.

Lucia: Maybe I will try the one-dive approach, with a buddy. I am still a bit scared of getting into cold water, because for me the gasp reflex happens even if I put my face only in the water. It is not so bad if I take a deep breath and hold it, and much worse with empty lungs.

DD: I fully empathise with the dislike of cold water immersion. The reason I mentioned it was because I assume your available pools aren't really warm and the pumps keep moving the water around. The ideal would be very very warm at the surface (6" 15cm) and quite cool just above the pool floor, with the water almost still and thermally stratified, like in a sunlit tropical lagoon completely surrounded by reefs.

By breathing up, and then filling the lungs with air, the body's sensors read "low CO2 so plentiful O2", and keep burning O2 at a regular aerobic non-MDR pace.
Then when the CO2 rises due to the fast O2 burning, contractions or air hunger starts.

OTOH, having the MDR/gasp occur right away with empty lungs forces O2 conservation, burns O2 slowly and builds CO2 slowly. This registers in your mind as discomfort because you haven't gradually habituated to it. The same physiological gasp that tries to suck in air to the lungs is actually pumping O2 from the extremities. By sealing the mouth and nose (with tongue in back), the coldwater gasp has nowhere to come from but the blood cells and muscle cells rich in O2 in the limbs, biochemically kicking them to move faster towards the core to ease the pH differential.

Lucia: Interesting. That makes sense. I remember that when I was a kid, if I was outside and there was a cold wind blowing, I would get an uncontrollable apnea reflex, which was unpleasant but bearable. It must have lasted for a few seconds. It still happens occasionally, but much less. It was very similar to the feeling I now get when I put my face in cold water.

DD: Right, the fast combined thermal and pressure change on the face, and also in the throat triggers the reflex.

When you hold your breath with full-lungs, I think you are getting about 1/2 of this effect due to air pressure on baroreceptors in the mouth/nose/throat/lungs.

When you did empty-lung breath hold, that 1/2 effect was missing, so you only felt the struggle phase, without the benefit of the 1/2 effect.

What I've been saying, is that by first being warm and dry, and knowing that soon you will again be very warm in the shower afterwards, then, casually diving in slightly cool water, that if you relax and accept the "switch-over" discomfort, knowing that it's just a temporary adjustment your body makes as it "becomes one with water" (no longer bothering to carry this huge "bubble" of excess air in the lungs down under the surface), and let your body feel the water as you glide through, and limbs smoothly power you along, and then rising up again to the surface, you are fully aware and sensitive to your immediate environment, and gracefully exchange the gift of air. Upon contacting the surface, you will want to exhale, but don't push it out, just exchange it gratefully.

As you climb out of the pool, your body which was adapted to the cool water during the dive, is now warming up due to the aerobic metabolism required to deal with moving in regular terrestrial gravity, so do a brief stretch of arms and legs and trunk, and a moderate aerobic breathe-up (no forced inhale, just a yawn), this should give a blush or flushed face and a tiny sweat reaction (the opposing reflex of the gasp), and then go take a warm shower and dry off.

Actually, I think that both of these reflexes release biochemicals into the bloodstream including micro-doses of endorphins and natural steroids, that help relax during stress.

Anyway, like I said, if something doesn't sound or feel right, don't do it, take time to figure out what's happening. Don't rush a dive, relax a dive. Those super-fast dolphin's ancestors 50 million years ago were once very slow divers too, as were our ancestors at the seashores 1 million years ago. It takes time. Dive with dolphins, backfloat with sea otters, blow bubbles with koi, breathe.

The thermoreceptors and baroreceptors of the face, mouth, throat are involved in the early part of the MDR empty lung dive.

The chemoreceptors in various places where blood flows through are involved in the next part of the dive. They are affected by the pH changes, as CO2 accumulates, diaphragmatic contractions and/or air hunger due to higher CO2 concentration gets stronger. It is the MDR gasp all over again, but this time triggered internally at the core, rather than externally at the skin surface of the face.

Since most people aren't used to making their blood send O2 more efficiently, we tend to get a "shock" when getting contractions. But the contractions simply move O2 towards the lungs. By propelling while matching these contractions to a whole body undulation or kick or arm stroke makes them less noticeable and might even add some extra oomph with no additional energy or oxygen consumption.

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