Improving my SAC rate

[Wathdoc]

Trim, correct weighting and being relaxed are vital to reduced gas usage. Fitness is important in more difficult dives and for simple immersion which has its own cardiovascular effects. For me , on a day to day basis fitness helps on a boat and especially the shore as you start the dive. If you are on a RIB bouncing around trying to kit up, swim on the surface to the shot line and decend, its surprising how much air you then use in the first quarter of a dive until you settle. For this experience, and strength helps.
Again for me, when my weight is less I am more flexible which as others say makes things easier.
Don't stress before you get in about your SAC, anxiety does not help at all.

 

[Blackcrusader]

Being super fit is not a way to improve sac rate. Better diving techniques are. Like not chasing the marine life, letting currents carry you rather than diving into currents, and generally dive very slowly and not like some people that think they need to be swimming. Even if I am going slowly in the current I get more time on my dives and also that means more time to get in some good videos or photos. This dive below with a guide I frequently dive with. We planned to do a wreck dive ( this was the 16th dive on the 6th day of back to back diving of 3 dives a day. We decided to just dive to 50 bar rather than time limit. Started with 210 bar on 80 cubic foot tank.

We got our boat captain to drop us over the wreck and then we dove to that, then slowly back up a sandy slope, you can see a brief time at 12 mins where I found two rare sea horses to get photo's of, then slowly up to the reef wall which we followed along.

Total time 93 minute dive. Funny thing was that after we were dropped off the boat went back and picked up an instructor and two AOW students. They completed their one hour dive and had to wait 10 minutes on the boat for us. When we got back aboard the students asked where we were as they we weren't with them when they came out. We said we dropped off before them. The looks on the faces was priceless. You did a 34m wreck dive and then the reef and still have 50 bar after 1.5 hours?

I weigh 135kg so not a light chap. 185cm tall nearing 60 years old. People assume I use a lot of air. I just have 36 years of diving and do around 150 dives a year atm. Off for another 45 dive trip to Bali in two weeks. I tend to do 30 - 50 dives per vacation over 2 - 3 weeks each trip.

You will really improve if you can do multiple dives like I do in a dive vacation.

 

[Blackcrusader]

Is there anything I can do out of water to make my air go farther? Obviously, being slightly in shape is better than completely out of shape helps. I am a relatively new diver, but long time fitness person, so I'd like to adjust my routine more towards what will help me dive better when I set goals for the New Year.

As a new diver the best way to improve is to do lots of diving. Don't worry about improving your SAC rate just get into a really good understanding of yourself. Are you totally relaxed on the dive? Dive with people who are better than you are and watch how they dive. You will see divers who don't seem to fin a lot but get to the same spots as you do. The best divers are not moving around or swimming a lot on dives.

 

[The Chairman]

Feet up you are out of trim and are fighting and using energy and diving gas to keep those feet level with your body.

This isn't true. Trim has to do with your torso being mostly horizontal. My feet are almost always above my head, but then, I bend my knees at almost right angles to my body. My resting position, if I'm diving with a long steel tank, is my heels slightly resting on the butt of my tank. I do a modified frog kick, not a flutter and my thrust goes parallel to my body. The problem I see with many ow divers is the 30 to 45 degree downward cant, with their fins way below their body. Consequently when they kick, they push themselves up as well as forward and have to vent air to compensate for that upward thrust. Once they stop, they find that they have to add air to stay mid water. Not only does this waste energy, since some of the thrust pushes you up, but you have to waste a lot of air adding and venting to maintain neutral buoyancy.

 

[Angelo Farina]

Buoyancy, trim, kicking and breathing are all connected together. If one of these 4 factors gets out of control, it will adversely affect all the others.
And yes, only experience and training (and possibly a good instructors) can improve all of them.
What is wrong is to focus only on one or two of the 4 factors. For example trying to have a deep control of breathing without reducing the effort caused by improper buoyancy and trim or inefficient kicking is not going to work. Similarly, without proper breathing control the buoyancy will always be out of control, particularly for people with large lungs, which cause extreme buoyancy variations.
What I am particularly sensitive to is the interaction between kicking, buoyancy and trim, as the Chairman explained here above.
In many didactic approaches, buoyancy and trim control are practised with very minimal kicking, in static or quasi-static conditions. The student is trained to stay still in water, almost horizontal (but not really horizontal as he looks forward), with arms partially stretched forward in a poorly hydrodynamic position, with legs flexed (knees at 90°) and fins well above the body. Something like this:

While this works well if the diver is still, or moving very slowly, the buoyancy and trim will be severely affected when there is the requirement of moving fast, kicking vigorously. If the thrust given by kicking is not aligned with the direction when one has to move, the diver will need to counteract the positive or negative thrust by changing the BCD buoyancy. The arms stretched at 45° will work as the spoiler of a Formula-1 car, making the head to go down when you are moving fast.
The result will be to waste a lot of energy in counter-opposed thrusts. Add to this that most people are not equipped of proper fins (proper for their legs, everyone needs different fins), and are not trained to using them properly (How many fin-swimming instructors are here? Have you ever made a fin-swimming course?).
This results in another amount of energy wasted in inefficient propulsion.
All this energy requires to be created by burning glucose in your muscles, this requires oxygen and produces CO2, and the latter stimulates a lot of breathing, hence SAC explodes...
And without breathing control, the high CO2 will stimulate short breathing, or even dyspnea, which again is inefficient, not removing well CO2 from your blood, albeit wasting a lot of air. You need well controlled deep breathing, with an asymmetrical cycle, for maximum CO2 elimination.
It is all connected, as said! But for learning proper DYNAMIC buoyancy and trim, current didactic approaches are of poor value, as they are STATIC.
A good freediving course, instead, is where you probably can find good training about dynamic control of your body, learning how to move quickly and efficiently, minimizing CO2 production and hence the need of breathing. Here you see the proper dynamic trim of a good freediver swimming horizontally. Compare this with the photo above and you learn how static trim has little to do with proper dynamic trim:

 

[The Chairman]

While this works well if the diver is still, or moving very slowly,

Going slow is essential to increasing SAC. Using muscles more requires you to breathe more to replenish oxygen and remove CO2. The slower you go, the more you'll see and the longer you'll be able to stay. No need for forced marches underwater. Take your time. You won't be able to smell the roses, but you'll be more relaxed during and after the dive as well as having more fun.

the buoyancy and trim will be severely affected when there is the requirement of moving fast, kicking vigorously.

It doesn't have to be. However, if you switch from the frog to flutter, then please stay far away from the bottom.

Currents are mitigated by proximity to the bottom. You'll find that you need less propulsion the closer you get and especially so if you're down in a channel. Bear in mind that the closer you get to the bottom, the more you need to use anti-silting techniques and abandon the flutter kick. This means getting your fins as high as possible and using the modified frog kick. The frog kick not only conserves air by being efficient, but it also gives you amazing control. You can swim forward, left, right and even backwards without waving your arms around like you're swatting at a flock of skeeters. If you don't know how to frog kick, go dive with a caver. We're addicted to it and our SAC shows that. You can also find some excellent tutorials on youtube. You have to make a commitment to learn it, and that means practicing it. In the beginning it will ruin your SAC, but once you get the feel, it will be like the magic switch. Here's a hint: the power of your frog kick will be felt on the bottom of your toes. Flutter kick is the opposite, where you really feel the power on the top of your toes during the down stroke (free-diving fins excluded).

 

[leadduck]

Strange, some seem to think that fitness doesn't mean much for SAC.
How much air must be ventilated (SAC) to exhale 1L of CO2? This ratio (ventilatory efficiency) is not constant and not the same for everyone. With increasing exercise, everybody reaches a level (anaerobic threshold) beyond which hyperventilation sets in and ventilatory efficiency gets worse. Physical training raises that threshold.

All this energy requires to be created by burning glucose in your muscles, this requires oxygen and produces CO2, and the latter stimulates a lot of breathing, hence SAC explodes...
And without breathing control, the high CO2 will stimulate short breathing, or even dyspnea, which again is inefficient, not removing well CO2 from your blood, albeit wasting a lot of air. You need well controlled deep breathing, with an asymmetrical cycle, for maximum CO2 elimination.

IIRC, PaCO2 is actually quite low beyond the anaerobic threshold due to hyperventilating, but it's the lactic acidosis that stimulates breathing as well and keeps you hyperventilating.

 

[wnissen]

Also, I have noticed ones with lots of yoga are use to deep breathing and blow through the diving gasses. If you have had yoga that is good because you are probably fit - just be aware of your breathing. If you are relaxed in the water you will have shallow breathing and therefore breath less gas.

I would be really wary of telling people to breath shallowly. If you're not emptying your lungs well you run the risk of a CO2 buildup.

 

[Angelo Farina]

I would be really wary of telling people to breath shallowly. If you're not emptying your lungs well you run the risk of a CO2 buildup.

Exactly. Shallow, fast breathing is the worst. Instead, You should breath quite slowly, but always employing almost all your volume and exhaling all the dirty gas. 2-3 cycles per minute, with at least 4 liters per cycle.

 

[Ana]

It looks like the board is telling the OP that there's nothing to be done other than keep diving. Even when it was clear that this person for whatever reason is not going to be diving for some months, the response is "go diving"

By now we are halfway on page 3, so we are due for the "my trim is better than your trim" and "deep breaths are wasteful vs shallow breaths are dangerous"

Well … I'm the last person to talk about SAC rate because I don't measure it or worry about it, but is very rare that I have to come up because I'm low on gas.
I have been diving most of my life so the comfort level and decent trim is there, what makes a huge difference for me is being in shape, the time my thyroid went bonkers and I gained weight, my air consumption went up considerably.
Now since I'm back to my proper weight what I notice is greater enjoyment when I keep up with strength training. Having the ability to gear up in our small boat without requiring help, being at the edge of falling down, or dropping stuff on deck feels good. To the point that we have opened the envelope of what sea state are doable for us, that in turn allows us to dive more.

In this case, I would ignore the muscle using more oxygen than fat bit. Go for strength with cardio in the middle, and avoid being overweight. No diver ever hopes to be weaker or fatter.