Bcd filled with water

[The Chairman]

Tidal volume seems smaller than people claim here. 500 ml of volume is a little over 1 lb

Tidal volume is not the same as total lung volume. from An Overview of Lung Volumes And Capacities (Vital Capacity)

A human lung can hold a maximum of six litres of air. The volume of air involved in the breathing process can be evaluated with the help of a spirometer. It is equipment which is used to examine the total volume of air inhaled and exhaled by the lungs. It is also used in testing the pulmonary function.​

When I taught Scuba, my final test before my students could go to open water consisted of adjusting their buoyancy by adjusting their breathing using 2-pound weights. They picked up a 2pound weight and adjusted their breathing to remain neutral. Then another. Then another. Until they can't remain neutral any longer. Then they had to dump the weights 2 pounds at a time, while still remaining neutral. Women had to be able to handle 4 pounds and men 6 pounds. One student managed 14 pounds while my best is 18 pounds.

To do this, you have to adjust where you stop and start your tidal volume. It's actually quite easy, once you realise just how to do it using your chest muscles only. Playing with weights in a pool is a good start. One precaution: Don't ever close your glottis. What's a glottis? You use it when you cough or hold your breath. Keeping it open is key to prevent any possible barotrauma. Just use your chest muscles to adjust your buoyancy.

 

[John Bantin]

That's utter nonsense John. I'm displacing way more water at any depth now a days
So much they think its spring neaps early. Besides what the heck is an ABLJ?
some kind of gastric band to counteract the changing buoyancy.
Just glad you're still kicking. Iain M

Hi Iain, a lot of Americans do not understand our sophisticated humour (humor)!

 

[John Bantin]

Tidal volume is not the same as total lung volume. from An Overview of Lung Volumes And Capacities (Vital Capacity)

A human lung can hold a maximum of six litres of air. The volume of air involved in the breathing process can be evaluated with the help of a spirometer. It is equipment which is used to examine the total volume of air inhaled and exhaled by the lungs. It is also used in testing the pulmonary function.​

When I taught Scuba, my final test before my students could go to open water consisted of adjusting their buoyancy by adjusting their breathing using 2-pound weights. They picked up a 2pound weight and adjusted their breathing to remain neutral. Then another. Then another. Until they can't remain neutral any longer. Then they had to dump the weights 2 pounds at a time, while still remaining neutral. Women had to be able to handle 4 pounds and men 6 pounds. One student managed 14 pounds while my best is 18 pounds.

View attachment 830731​

To do this, you have to adjust where you stop and start your tidal volume. It's actually quite easy, once you realise just how to do it using your chest muscles only. Playing with weights in a pool is a good start. One precaution: Don't ever close your glottis. What's a glottis? You use it when you cough or hold your breath. Keeping it open is key to prevent any possible barotrauma. Just use your chest muscles to adjust your buoyancy.

Be cautious of hard and fast statements. A person who is 6'5" and a lifetime non-smoker will have a much greater vital capacity than a 4'8" man who has smoked 40 untipped cigarettes nearly every day of his life.

 

[The Chairman]

Be cautious of hard and fast statements. A person who is 6'5" and a lifetime non-smoker will have a much greater vital capacity than a 4'8" man who has smoked 40 untipped cigarettes nearly every day of his life.

So far, none of my students have done just the minimum. I find the issue is not with size, but with confidence. A confident student nails it, and mind you, those who were not already confident, never gets to do this test. I have a few exercises for the non-confident diver that work pretty well.