Tuesday, June 29, 2010

Dive Reflex, Spleen Shrink and Freediving

Last night I sat in the bath with my son, Zephyr after the other two kids got out. He began sticking his head in the water an holding his breath.
Soon he wanted his mask and came back with his sisters one. He did a few half minute holds with face in the hot water.
I took control as he had forgotten to breathe up, and relax. The water was hot so I had him sit next to the bath and breathe slow and deep for a while - then he did a 45 second hold. Next he was relaxing a bit and prematurely began the dive only making 30 seconds - a good reminder that stillness and calmness combined with a good slow breath-up helps. Again I took control and had him relax for two minutes with slow deep breathing. He also put his face in cold water - "I need to be cold, Dad!".
He has realized that body temperature is critical to breathholds - too cold is bad as well as too warm.
Anyway he managed 1 minute and 3 seconds.

That reminded me I wanted to post on some aspects of relevance to us spearos or freedivers.

I read many journal articles a while back - some interesting studies were done.
Spleen volume was measured during dives and breathholds - it drops up to 20% during dives releasing oxygen carriers - haemoglobin. The studies showed that divers can gain an extra 3% of haemoglobin in their blood through such spleen shrinkage -that helps extend the breath.
Typically the release occurs over about 3 dives with a typical 2 minute rest in between. This goes some way to explain why freedivers and spearos do warm-up dives.
Its more like haemoglobin release dives.
The raised haemoglobin levels would persist for some time but would usually drop to normal some 10-20 minutes after the last dive or breathhold.

I feel these effects readily in my body - the first few holds or dives are generally tougher than the 3rd or 4th. In dry training it show up too - for instance on exhale or inhale holds there I work my diving muscles I often only get to 50 to 60% of what I reach on attempt 3 or 4.
Pity I did not have this info when I did athletics - a 400 m or 200 m sprint would surely be better performed if a few breathholds were done in the 10 minutes before the event.

The dive reflex or bradycardia is deemed to be a independent of the spleen shrink though both are experienced in freediving. The dive reflex refers to blood shift from limbs to the thorax and brain combined with slowing of the heart.

Cold and breathholds
I find I need coolness to do breathholds, but my bodies core temp must not fall too far. I did some exhale exercises a while back while in the snow at Hogsback and in short order I found I was stripping off clothes quite fast even thought the temp was only around zero with wind.
Cold water in the face and on limbs helps with the dive response(slowing of heart and blood shift to thorax).
As with me Zephyr also like the coolness.

I read in one article Martin Stephaneck's warm up dives were as follows:
A dive to ~15 with a 2 minute bottom time, rest of 2-4 min
A dive to 30 m with 2 min bottom time, rest 2-4 min,
An exhale(full exhale) dive to 15 m with minimal bottom time, rest 2-4 min
A second exhale(full exhale) dive to 15 m with minimal bottom time, 8 min rest
A dive to 109 m!

See how his dives capitalize on the spleen shrink that occurs over the first few dives.
Also those exhale dives surely give a good simulation of what he will feel like when approaching 100 m.

Notice that he keeps it safe on the exhale dives which are much shorter than the inhale dives.

One important aspect we as spearos and freedivers should not overlook is feeling the signs in our bodies. Can you feel when you have overdone a dive and you are moving into suspect territory where blackout is imminent?
I did some running the other day and included a few exhale jogs. Twice I got to very close to blackout and even had a samba on my final 95 step jog on full exhale. My vision began fading back and forth and my muscles were screaming for air. My one and only samba in the sea was back in 1992. Safety is very important to me - especially with increased responsibilities of family etc. I thus always take is relatively easy in the sea and never get near the stress levels (i.e. oxygen desire of excessive CO2) at sea as on land. On land I may pass out but will recover - still it is good to train where you will be safe if you fall.

So I say it is better to push hard on land where things are safe(in the bath is not land! - Breathholders have drowned in their own baths!).
Get to know you limits and dive well away from those limits in the sea.
If you must push it then have COMPETENT back-up and systems in place especially in our dirtier current plagued waters.


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