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DAN Europe Medical Q&A
from Scuba Diver #55
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DAN medical specialists and researchers answer your dive medicine questions
Does a physically fit (athletic) diver consume air faster on a dive than an average person with a sitting lifestyle?
Q: I have been working as a dive instructor for over ten years now and I noticed that throughout the years, the more physically fit I became, the more air I consumed. I was always fit, but constantly been doing more exercising. Does physical fitness affect it? Does it maybe depend on a type of exercise?
A: Physical fitness level is one of the factors that can influence the oxygen requirements of the body and so your breathing rate during a particular exercise/effort level because a higher aerobic fitness (cardiovascular endurance) means an increased efficiency of the body in its ability to deliver oxygen to your muscles. VO2 is the usual index of the body’s efficiency at producing work and the measurement of VO2max is an indicator of one’s aerobic fitness.
However, many other factors influence breathing gas consumption during a dive, such as physical size, work load, water temperature, use of drugs, stress and anxiety, excitement, general physical and emotional state.
Also, as the Boyle’s law applies, there is increasingly less volume of gas available to the diver as the diver descends in the water, as you are aware, the actual volume of gas within a scuba cylinder does not decrease as the tank physically does not shrink under pressure. However, gas being delivered to the diver is at ambient pressure. This increased pressure means there are more gas molecules per unit volume as the gas is more dense and the diver consumes more molecules per breath, resulting in the gas in the scuba cylinder lasting a shorter time than at a shallower depth.
In conclusion, your gas consumption rate will change based on your personal comfort during that dive, your actual physical fitness and health on the day, and your personal experience as well as the dive conditions themselves, such as dive profile, temperature, currents, etc.
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