Exertion/buoyancy relationship

[InTheDrink]

A quickie.

I believe that exertion causes you to become buoyant.

Reasoning is straightforward but retrospectively fitted from experience but would be good if could be validated or thrown out.

Under stress or exertion one tends to hyperventilate to some degree. The ratio of time for breaths in to time for breaths out increases - that is, more of the time you are breathing in and exhaling rapidly so as to get your next gulp of air. This means that you have more air/gas in your lungs more of the time and this makes one positively buoyant where one wouldn't have been before.

I believe this to be correct and certainly experience would appear to validate this. I can hold forever at 5m with my heart close to rest. Factor in some anxiety, current or any workload that increases heart rate changes this quite a bit in my experiences.

However, before proposing this as a hard and fast rule to any potential friends/buddies I'd be interested to get feedback. Maybe it's something else.

Thanks,
John

 

[spectrum]

Under stress or exertion a divers lungs will tend to "pump up" This one way divers get into inadvertent ascents when things go south. They don't even realize they have initiated an ascent until well under way.

Remember that lung volume is never a constant so your actual buoyancy is an average of a lot of things.

I'd say your observation is right on.

Pete

 

[RJP]

I think you're essentially close, but less about hyperventilating, average lung volume, tidal flow, etc.

It's a lot simpler than you're making it out to be: upon exertion - or even just when focusing - you tend to hold your breath.

I see it all the time with students: the instructor points to them to do a skill and what do they do? They take a big breath and hold it while doing the skill.

I saw it recently with a buddy in my Tec course. Everytime we did a no-mask drill or air share he'd take a big breath and hold it while doing the skill, at least for a few seconds to get started. And as Pete points out, by then you're ascending and now you have no mask on, you're sharing air, and your ascending. Becomes problematic pretty quickly.

 

[TSandM]

With exertion, you need to increase your minute ventilation, or the total amount of gas that passes through the gas exchange part of the lungs. If you do this by simply increasing your breathing RATE, your buoyancy will not change. If you take deeper breaths, but also exhale further, your buoyancy will not change. If you start to get out of breath, you are likely to take deep breaths but not fully exhale, so the average volume of your chest increases, and you do become more buoyant. Learning to control this is part of learning buoyancy control when actually diving.

Anything that makes a diver anxious is likely to make them start to use an ineffective ventilatory pattern, where a deep breath is taken but only a small part of it is exhaled before inhaling again. This DEFINITELY makes the diver positive, and is largely responsible for the buoyancy issues people have when task loaded or nervous.

 

[ligersandtions]

At the end of my dive the other day, after we finished the safety stop and were making our way up slope to ~6 feet of water (to avoid the surface swim), I stopped my buddy and motioned to him that I was going to do a mask removal and replace drill (I was in about 10 feet of water). I was neutrally buoyant before going into the skill. Then I removed my mask and all the sudden I started feeling floaty....I didn't have good enough reaction time to recover before I surfaced. By the time I cleared my mask and looked back down to make sure my buddy was okay, he was giving me that "what are you doing and why did you surface when we still have a ways to go" look.

I would agree....on skills that aren't necessarily second nature to you and require you to really focus on them, you tend to inhale more than you exhale, which then causes you to become positively buoyant. This is a skill I will work on until I can manage to do it with perfect buoyancy....god knows I don't want this to happen at depth, nearing my non-deco limit or something like that.

 

[InTheDrink]

RJP. I agree that holding your breath will make you buoyant from a neutral buoyant situation. That's not the scenario I'm talking about tho.

TSandM - aside from saying we must stop meeting like this, people will talk - I think you are right and I knew I had used the word hyperventilation incorrectly. I meant net volume of air in the lungs, or however you said it . In the situation I'm describing, breathing out tends to be quick and shallow, breathing in tends to be voluptuous, if that adjective can be used in this context.

My question here then is: when I'm working against a current, I'm fine at my own pace. But when others race ahead, I end up in this situation. I try to go slow, rest etc. but if they don't wait - and you've got bad vis etc. - keeping up is sometimes a necessity. But a real pain. So this isn't task overloaded, or stressed (apart from being p**ssed off people are racing off!), but simply exertion. But of course exertion causes many of the same physiological reactions as anxiety - such as rapid breathing. Irrespective, the overarching point is that rapid breathing negatively affects your buoyancy in a positive, buoyant way. Which in turn adds to stress, which in turn...etc. etc.

Any suggestions for how to avoid this scenario? Apart from smoking less, going to the pub less and doing more exercise. And bashing people who race ahead?

John

 

[Bubbletrubble]

At the end of my dive the other day, after we finished the safety stop and were making our way up slope to ~6 feet of water (to avoid the surface swim), I stopped my buddy and motioned to him that I was going to do a mask removal and replace drill (I was in about 10 feet of water). I was neutrally buoyant before going into the skill. Then I removed my mask and all the sudden I started feeling floaty....I didn't have good enough reaction time to recover before I surfaced. By the time I cleared my mask and looked back down to make sure my buddy was okay, he was giving me that "what are you doing and why did you surface when we still have a ways to go" look.

@ligersandtions: I commend you for practicing mask removal and replacement. You did the right thing in communicating to him what you were about to do. But what the heck was your buddy doing while you were ascending through the water column? He should have been yanking you down and preventing your inadvertent ascent. While you're doing the mask R&R, he should be watching over you -- more so than usual. He should be anticipating that you might lose control of your buoyancy. Simple as that.

Have fun and dive safe.

 

[Bubbletrubble]

My question here then is: when I'm working against a current, I'm fine at my own pace. But when others race ahead, I end up in this situation. I try to go slow, rest etc. but if they don't wait - and you've got bad vis etc. - keeping up is sometimes a necessity. But a real pain. So this isn't task overloaded, or stressed (apart from being p**ssed off people are racing off!), but simply exertion. But of course exertion causes many of the same physiological reactions as anxiety - such as rapid breathing. Irrespective, the overarching point is that rapid breathing negatively affects your buoyancy in a positive, buoyant way. Which in turn adds to stress, which in turn...etc. etc.

Any suggestions for how to avoid this scenario? Apart from smoking less, going to the pub less and doing more exercise. And bashing people who race ahead?

John

@John: The scenario you describe (buddies getting too far ahead of you and you feeling compelled to overexert yourself to keep up) is a classic example of poor buddy skills -- on their part. You should really have a talk with your dive buddies. Under poor vis conditions (< 10 feet), they should be looking at you every couple of kicks. How else will they know where you are and whether you need their help? The team should move at a comfortable pace for everyone in the group, which usually means as slowly as the slowest person wants to go. Diving isn't a race. In fact, your dives will last much longer and you'll see more macro life if you go more slowly. I've done some dives during which I swear the nudibranchs are moving faster than I am.

Kelp diving here in Southern California teaches you many important lessons in being a good buddy. Depending on how thick the kelp is, your buddy team may have to pass single file through a wall of kelp. If my buddy is behind me after a pass through a "kelp restriction," I pause a few seconds to see that she/he is clear before kicking on. Kelp by itself usually isn't a big problem even if a diver gets entangled in it. It breaks easily by hand. What makes me more concerned is the stuff that gets caught in kelp -- like fishing line.

There are several useful techniques that you can use while kicking into a current. It's easy to cramp up when you're overexerting yourself, so switch up your kicks every now and then. Duck in behind a rock formation to hide from the current. Grab onto a rock to maintain your position without getting dragged back by the current. Consider lightly holding some kelp if it's handy.

Being in good aerobic shape will, of course, also help. Keep in mind that working against a current should be allowed for in your gas planning and management.

Have fun and dive safe.

 

[InTheDrink]

Thanks Bubbletrouble. I agree with you wholeheartedly, diving is not a race! And it's not a swim either. In general I feel if I'm swimming I'm doing something wrong.

I'm actually not in bad shape (or at least I look fairly fit) but I like to dive slow and look around. In the instance I'm talking about it was the instructor and DM that raced ahead. If I had known the site I would have let them go and do their thing and hung back, but I didn't know the site. I did rest, pulled myself along on rocks, and changed finning. But every time they kept running ahead. I think your best advice, along with swapping finning styles, is to tell them after to slow the funk down.

In terms of ducking current, I'm your man. I hide behind anything. I dive 1 inch from the deck. I've even got a reef hook which I use in ripping currents when photographing shark. But when someone's racing ahead welll, guess I've got to let them. Just a worry when you're being guided and don't know where the exit is. But ultimately I think you're right - it's their failing.

Thanks for your post and long may the nudibrachs out run you

J

 

[TSandM]

Jclynes, I think you have figured it out. Diving is like dancing; you need a partner who is on the same wavelength. If you're a nudibranch lover, and try to dive with a spearfisherman, you are going to be unhappy, and he is going to be unhappy, and nothing in the dive is going to go well.

Now, an instructor and DM should have modified their own dive procedure to adapt to a buddy who was having trouble keeping up . . . But as my experience with my own early dives went, I spent a lot of time kicking like a madman, trying to keep up with the professional who was "leading" the dive, from about twenty feet in FRONT of me.

One of the things that's good to do in the initial (on land or on the boat) discussion, is to talk about how you like to dive. You might be very happy paired up with a photographer. While he is shooting, you can be scouting the local area for the next target (this is a role I often play).

The one thing that is sure is that, if your level of exertion gets too high, you will not enjoy it. Whether it's losing your buoyancy control (which I don't do when overexerted) or CO2 retaining (which I DO do when overexerted, and it makes me sick and it isn't fun), it's not comfortable, safe, or desirable. The solution lies on the surface, with the pre-dive discussion, and with establishing a signal you can use to let your buddies know that they are outrunning you, and you aren't happy.