Still have unanswered questions on oxygen depletion:

You can get 5-10 sec from burning CP in muscles. Anaerobic(glycogen in muscles to lactate) will give you another 20-40 sec,but will also make the muscles acidic. After that you need aerobic metabolism,which releases more energy(ATP goes to ADP) but is much slower. What gets you holding your breath is CO2 build up.Low oxygen will slow you down and make you short of breath but is really hardly noticeable.

I'll shoot from memory here... I think this is related to your muscles going the anaerobic route when the O2 runs out (not enough oxygen to sustain aerobic state). When you go anaerobic your mitochondria produce far fewer, perhaps a third, ATP (Adenosine Triphosphate) molecules (energy) and you get the sensation of hitting a brick wall or dragging a piano. In addition, this fermentation process leaves you with muscle burning lactate to dispose of. It's incredibly inefficient compared to aerobic ATP production and that is apparent in short rest sets or all out swims. If I am wrong, I am sure somebody here will set me straight!

Kevin,GREAT:applaud: I tried to say what you said but you said it better.

Right,it is metabolic. All three energy systems are working all the time,but the first 2(CP and anaerobic) are depleted faster than they can recover relatively quickly at high intensity work.The rate limiting step then becomes aerobic metabolism and thats as fast as you can go. Re;the question of no breathers,all the research I know of says they are of no value,but that seems unlikely to me. In a sport where breath control is important,drills that improve it would seem helpful to me.

So allen, after so many seconds we go aerobic, but that fact doesn't mean we need more oxygen on the intake end, but we will use the oxygen already available and what slows us down is purely at cellular level, right? So the terms oxygen debt, or oxygen depletion which sometimes are assumed to be at the intake level are actually at the metabolic level. Maybe the Tennesse Turns (hold breath from flag on, turn, only breathe when past flag on the way out) will make your mitochondria more efficient? Or maybe it will make your mind used to having your C02 higher? I believe what we have here is a lack of communication! (Cool Hand Luke {circa 1967}) We use the terms "oxygen hunger", or "lack of oxygen" trying to explain something in the respiratory end of the equation, but truly the problem is in the metabolic end and we haven't that much control of it. Is this a question of physiology or semantics? Thanks, so far, let's get more input. billy fanstone

Put simply, aerobic is the state in which you can maintain exertion for an extended period of time. If you exceed the aerobic threshold you will be in the anaerobic threshold and your ability to sustain effort using this production method is limited to less than 2 minutes. Now, when you feel the need to breathe does that mean that you have crossed the line into anaerobic? Is the urge to breathe a warning that you are about to cross over into anaerobic? Comments from internists?

You know Allen, I use to wish there were a drug which would make you better psychologically at playing tennis but without any side effects. A drug that would take away the control of the super-ego over the ego, letting my id play on automatic. Much like the book "The Inner Game of Tennis" teaches. The other drug would be one similar to opiods which would take away the urge to breathe, but without side effects also. But lo, this is not possible. Imagine swimming and having your pC02 climb up above 42 to 45-50, maybe 60. Still you would have muscle fatigue, but you wouldn't be aggravated by the urge to breathe. Well, better stick to strong coffee as the only permitted drug. Cheers, billy fanstone

Put simply, aerobic is the state in which you can maintain exertion for an extended period of time. If you exceed the aerobic threshold you will be in the anaerobic threshold and your ability to sustain effort using this production method is limited to less than 2 minutes. Now, when you feel the need to breathe does that mean that you have crossed the line into anaerobic? Is the urge to breathe a warning that you are about to cross over into anaerobic? Comments from internists? The urge to breathe is primarily due to the build up of metabolic waste (CO2) as Allen said earlier. I forget the name of the receptors, but they alert the brain when there is too much carbon dioxide rather than a lack of oxygen. The three energy pathways: aerobic, anaerobic and non-aerobic (ATP-CP) are working all the time; however, the intensity of the bout of exercise determines the proportion of each. The initial jump/dive into the water uses the non-aerobic, immediate form of energy (creatine phosphate), which qiuckly gets depleated (5 secs or so). If you are sprinting, the fast muscle contractions need energy faster than the slow aerobic pathway can supply, so the anaerobic pathway will supply the muscles with ATP until you've depleated all the stored muscle glycogen. You know you've reached that point when your body starts to burn and you have no choice but to slow down. On the other hand, if you're primarily working aerobically and begin to increase the intensity, the point at which the anaerobic pathway begins to produce more H+ ions than the body can reabsorb is called anaerobic threshold, and the result will be muscle pain and fatigue, which will slow you down before it will allow you to use up your oxygen supply. Your brain will shut off conscious awareness before it will allow you to use up too much oxygen. Oh, and the mitochondria only come into play during oxidative phosphorylation (aerobic), and you can train the body to build the mitochondrial matrix so aerobic metabolism becomes more efficient. Anyway, blah blah blah...you can train the brain to not be so alarmed by the receptors telling it to breathe because of the buildup of CO2, which is why hypoxic (misleading name) training can be beneficial. The key is to relax into the speed and remember long slow exhales. And remembering that the urge to breathe or lack of oxygen is not what is slowing you down, it is the buildup of lactic acid.

^^ Excellent, thanks.