How "much" of air consumption is physiology? How to improve consumption?

[Joneill]

5'10" 185 lbs. My best is 0.27 cu ft/min on a couple of dives

That is a freakishly low SAC - impressive! My very first open water dive was 1.25 cu ft/min but with 150 dives now, I’m typically down to 0.4 - 0.45 and my lowest to date is 0.38. Still on a downward trend, but air consumption is no longer a concern while diving .

 

[lowwall]

Even big guys can do fine on air. Firefighters, no matter their size, tend to be great on air. It's all that training with SCBA gear and the fact that nothing they encounter underwater is going to stress them. Or take me. I'm 210lbs of lean muscle mass - overlaid by 50 pounds of lard. But my air consumption is very good despite having "only" 150 or so dives. It's been that way from pretty much the start. The key is I'm a former competitive swimmer which means I'm efficient underwater. I'm also extremely comfortable underwater, in addition to swimming practice I spent my summers as a kid playing underwater in pools and lakes and went on to be a lifeguard and white water rafting guide.

Like others have said the keys are to move slowly and generally relax. Just because you have more muscles doesn't mean you have to use them all the time. Also keep in mind that tensing your muscles is work and will use extra oxygen even if you're not visibly moving anything. The water will support you if you let it. Finally, it helps to exhale very slowly. Fewer breaths per minute means better consumption. It also forces you to breathe deeply which keeps CO2 levels where they should be and is calming in its own right.

 

[RayfromTX]

I sometimes dive with a really big guy that is always the last to ascend. He just doesn't work. He is constantly drifting along and watching others. He never chases anything and will often just hang vertically watching, other times in perfect trim and using little fin kicks to adjust.

I'm 6'2 and 180-185. I have always been in the water and comfortable. I am very fit with good lean muscle mass. (cyclist) I have a very high VO2 max and that helps with my efficiency. If you do heavy workouts, your metabolism works in the following days to repair and build. That takes energy and oxygen. Take it easy in the days before diving if you want to minimize this.

We move more than we think we do. Video will show you what you can't self monitor in this regard.

Comfort counts. Stay warm. If you feel a bit chilly at the end of the dive, your metabolism is working to keep you warm. Let your exposure gear do that. Add a hood or a vest or more neoprene.

My wife and I are usually the last back on the boat. On the 2nd or 3rd day of the trip we will be in the RMV range of .45 if we aren't focused on it and if we work at positioning ourselves or fighting current sometimes. If I know I have been efficient, I may work during parts of the dive to position myself to get a shot. I may work harder to get myself into a spot where a subject will be passing by. I may see an eagle ray or large barracuda or something. I never chase but I may swim hard to get on the other side of a large coral formation and position myself to be at complete rest when they then swim by calmly. I have to decide if that expenditure is worth it and if I have the gas relative to others I'm with. Usually I can get away with a couple of expenditures like that though most dives I don't have any reason to. I'm almost always just being as meditative as I can be. Yoga can really help big guys learn to control their breathing.

Finally, if you try to limit your breathing you may build up CO2 which is what causes us to have to breathe. Our instinct to breath isn't because we need oxygen, it's because the build up of CO2 causes us to hurt from a build up of acids in our blood. It is the PH that makes us breathe. Limiting our breathing builds up CO2 and getting rid of the build up causes us to breathe more and the gain is lost. This is why it is suggested that we breathe slowly and deeply. Your goal is to efficiently collect CO2 out of your blood and exhale it. Shallow breathing is fine on shore but inefficient while diving as Scubadada eluded to in his excellent post.

@Compressor @rsingler did I get my description of breathing mechanisms correct? I always like to confirm my understanding with experts and these are two of the most knowledgeable on the board, being anesthesiologists by trade and being highly experienced divers.

 

[Miyaru]

The two biggest oxygen consumers in your body are your brain and your muscles.

The oxygen consumption of the first one, well there's nothing you can do to change that.
Oxygen consumption of the second one: depends completely on how much you move. Once the experience comes into play, you can think about every muscle movement, leading to less oxygen consumption -> less carbondioxide production -> slower breathing -> lower SAC-rate.

Until that amount of experience has been built up, use the first oxygen consumer as the perfect excuse for a high SAC rate: the smarter you are, the more oxygen you consume.

 

[Scraps]

“Being a bear of very little brain” like Winnie the Pooh, I guess I’ll take the first part of that as good news for my diving.

 

[Marie13]

My average RMV is 0.6/cft per minute. That’s in a drysuit with doubles in cold water. The lowest it’s ever been was 0.54 on a very relaxed quarry dive, but still drysuit, doubles, and cold water.

 

[stevensamler]

“Being a bear of very little brain” like Winnie the Pooh, I guess I’ll take the first part of that as good news for my diving.

Keep diving , more bottom time equals better SAC.

 

[scubadada]

My average RMV is 0.6 psi per minute. That’s in a drysuit with doubles in cold water. The lowest it’s ever been was 0.54 on a very relaxed quarry dive, but still drysuit, doubles, and cold water.

Hi @Marie13

I assume you mean 0.6 cu ft/min

 

[scubadada]

There is a longstanding poll regarding average RMV with almost 300 responses to date. If you have not contributed to the poll, consider doing so. Average Gas Consumption

 

[Lorenzoid]

At the point in your diving when you stop giving a hoot about how your SAC is going to affect this dive, your SAC will start to decrease.