Originally posted by Bob3
Good point there, 'gatorgal.
The "average" adult has a lung capacity of about 6 liters, which translates into a little over 13 lbs of buoyancy. If you swing only half of that from inhale to exhale, that's a difference of over 6½ lbs. Breath control is the key for the fine tuning of buoyancy.
Can't argue with you about the breath control, but just because I'm kinda into this stuff, I wanna point out that even though lung volume is about 6 liters for the average adult, that's not the whole story.
The lungs have a minimum volume that can never be exhaled.. this volume is necessary for the alveoli not to collapse due to the fact that they're fluid lined. This is called residual volume and is around 2 liters.
The difference between a regular exhalation and a total exhalation is called the expiratory reserve volume and is about 1 liter.
A *regular breath* has a volume of about 2 liters.
The difference between a regular inhalation and complete inhalation is the inspiratory reserve and is about 1 liter.
Total: about 6 liters, the maximum breath (as much as you can inhale to as much as you can exhale)is usually a bit less than 4 liters (that's the vital capacity). People generally only find it comfortable to breathe within the normal 1.5 to 2 liter breath range... take small breaths at high lung capacity or low lung capacity and your lungs will start to hurt, or take full 4 liter breaths and your head will start to hurt.
So, even though breath control is important, no one has to worry about their weight swinging up and down by 6.5 pounds while breathing
Wasn't that EXCITING?