What exercises can you do before Scuba Diving to improve your air consumption?
It has been a number of months since I last went scuba diving - short enough that I can still remember everything, but long enough for any diving specific exercise related things to have worn off.
If I dive for several days in a row, I find that my air consumption improves over the course of the dives. I'm sure that part of that is familiarity and remembering technique, but I have a hunch that some of it is more fitness and muscle related.
Are there any exercises / practices I can do in the week or so before I go diving, to help prepare my body to make my air last longer?
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There are three things you should look at here, lung capacity, oxygen carrying capacity and bradycardia reflex.
Lung Capacity
When I was younger I suffered from asthma, and had a series of lung exercises to improve lung capacity. I can't remember them all now so I checked various sites. This one has some excellent tips, including:
- Rib stretch
- Abdominal breathing
- Practicing slow breathing while exercising hard
Oxygen Capacity or VO2max
This is all down to hard exercise. The way trainers describe it is "performing very hard exercise for 5 minutes, then complete recovery, followed by another hard exercise, and repeating 3 times in a single workout." Complete recovery includes rehydration, expelling lactic acid, nutrition, and compression or massage! Doing this 3 or 4 times a week will really help to build VO2max.
Bradycardia
This will be second nature to you as a diver, but when exercising, having a little water splashed on your face will help your body automatically prepare for going underwater - do this when exercising hard.
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Practice and remaining calm underwater seems to be the key to reducing your gas consumption. Most new divers consume lots of gas due to the unfamiliarity of being underwater, novice skills, and the ubiquitous overweighting.
After a while, you learn to control your buoyancy and get your weighting correct: enough to stay down with a nearly empty cylinder (circa 30 bar) and no more. You also learn that winter diving means thicker undersuits / wetsuits which are a lot more buoyant, so additional weight is needed to counteract it.
With more practice you'll consume a lot less gas as skills become far more simple and an awful lot less stress.
Gas consumption is measured as the "Surface Air Consumption" rate (SAC rate) in litres per minute.
As we all know, for every 10 metres of depth, add 1 bar of pressure. So, at 20 metres, you'll be at 3 bar which is 3 times the surface pressure. If you have an SAC of 15 litres/minute, you'll consume 3x15 = 45 litres per minute at 20 metres, or 60 litres/minute at 30 metres.
Your SAC will vary greatly depending on what you're doing underwater. If you're vigorously swimming against a current, your SAC will easily double and could quadruple in extremis. Those numbers again: if you're really fighting the current your SAC could be 3 times normal, so using 15 as the base, this will be 3 x 15 = 45 which is then multiplied by the pressure, so at 20 metres this is x3, so you're consuming 135 litres / minute, or converting that to bar of a single 12 litre cylinder, that's about 11 bar a minute -- dangerously emptying the cylinder in 13 minutes (using 12 litres x 150 bar)
Compare that with a chilled-out drift or gentle bimble where your SAC would be normal (15 l/min) so using 45 l/min at 20 metres, or 40 minutes of gas.
With more practice and relaxation, you can get your SAC down to 12 litres/min (or 50 minutes for 150 bar of a 12 litre cylinder).
Tech divers tend to use two SAC rates; the "bottom" SAC where you're moving around, and the "deco" SAC where you're hanginging around motionless whilst breathing rich oxygen mixes. For planning, I use a bottom SAC of 15 l/min and 12 l/min for deco, but know I use less.
For 'fun' I brought a half-empty deco stage with regulators into the lounge one night and measured the amount of gas I consumed whilst watching the telly and doing some internet browsing -- must have looked odd with a reg in my mouth and a clothes peg on my nose! In that 20 minutes, my SAC was 7 litres/minute.
So, in answer to your question; you'll need to be moderately fit. But the main thing is to be relaxed, which is much easier if you practice your skills, especially the art of doing nothing - buoyancy & weighting. The more you practice, the better you'll be.
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As an assistant instructor, I suspect it's your relaxation rate. New divers, and those who haven't been diving for a while, tend to get more excited when diving, and may also try to see the whole ocean. Try slowing down and taking a closer look at what's around you. Ironically, you'll usually see more when going slow because you'll notice the small things as well.
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Personally I would say regular exercise routine with swimming and cardio will help improve your air consumption.
But the best exercise for scuba diving is more scuba diving. The more you dive, the more comfortable you will be and the more efficient your movements become underwater the lower your breathing rate will become.
practice not using your arms/hands underwater, practice more efficient finning techniques, make sure you are not over or under weighted, remember to check weight when you change gear, remember diving is not a race so swim slowly, breath deeply and slowly
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