Jim,
On blood volume, what I think you are meaning to ask is how do I increase red blood cells/hemoglobin, which is the part of the blood that stores and carries oxygen. Exercise is the number one way to increase red blood cells. If you are at all low in iron or magnesium, they can also be essential to increasing red blood cells.
Now the not so politically correct ways: blood doping and EPO. Blood doping was a complicated procedure where the athlete relocated to a high altitude place, which causes the body to increase red blood cells to offset the effect of less oxygen in the air. While there the athlete would take and store his own blood to be used a few weeks before the competition. If everything was done right, it worked, but even then it was very complicated and expensive for the athlete. A lot of people used to think the reason behind blood doping was to increase volume, but the real reason was to increase hemoglobin.
EPO has made blood doping a thing of the past. EPO is recombinant (man made) erythropoietin which is a normal protein made by the kidneys that stimulates the production of red blood cells. It was developed for anemic patients such as those undergoing chemotherapy, but has been a big hit in the endurance sports since it came out. Have you ever heard the TV ad for Procrit “so I have the strength to do the things I want to do”? - that’s EPO? One side effect that became apparent in the Tour de France was that if the red blood cells % become to large, it thickens the blood and can lead to heart failure. Not good!
Sydney Olympics was the first major sporting event where athletes were tested for it although everyone close to endurance sports new it was being used by most athletes the 10 previous years. The IOC claims it’s test can detect the presence of recombinant EPO, but from what I have heard from athletes the test basically compares the % of red blood cells to a standard that they have estimated is the highest red blood cell % a non-EPO user could obtain. This means that almost everyone monitors their blood and with adjusting their use of EPO, keeps it right below the standard. I’ve heard the main reason the Tour de France started testing was because they didn’t want another death on their hands.
Sorry I got side tracked a bit on your original question. I personal think hemoglobin has a tremendous impact on breath hold length in freediving. I would not worry too much about your amount of lean muscle burning your oxygen. As long as you didn’t take huge amounts of anabolic steroids, the lung expansion, oxygen conversion, and other benefits you get from building the muscle should more than offset any increase use of oxygen from the muscle.
Good training,
Don
PS I don’t advocate the use of EPO, it's just you can’t honestly discuss athletes hemoglobin levels without mentioning it since it has such a large and direct effect on it and its use is so prevalent.