Scuba diving should be in no way competitive. If you are part of a group of divers, you want everyone to have a good time. That said, the human spirit is without doubt naturally competitive and we will find ways to compete, however irrelevant. You’ll often see divers post-dive comparing how much air they used. Somehow it’s often seen as clever to use less than the next person. I was on a dive trip once where my buddy used exactly half the gas I went through. Did this mean he was a better diver? Another friend of mine was supremely fit. When his family came to visit, his wife and daughter would drive over from their home ten miles away but he would always prefer to run. The London Marathon? He completed runs across the Sahara! However, when we went of a dive trip together I was amazed at the rate of knots with which he went through his air supply. I put it down to poor technique at the time. Then I went away diving with a young television Gladiator, Hunter.He was young and fit and made me look totally puny by comparison. It was lucky he could easily manhandle an 18-litre cylinder because that is what we had to get for him to allow him any time underwater on the shallowest and most benign of dives. On the other hand, Umberto Pelizzari, formerly the free-diving world champion, uses yoga to reduce his breathing requirements to negligible levels. One quickly comes to realize that women generally use less air than men on dives. Is it because they are serene and become part of the underwater environment unlike men who tend to be more active? Or is it because they are usually smaller than men and thus have smaller lung capacities? I’ve dived with elderly over-weight ladies who went through less air than me, and a lot of other people, so it’s probably a combination of both. Recently, I was diving with twin-cylinders on a deep dive in Truk Lagoon. A rather large lady of a certain age did the dives with a single 11-litre cylinder of air while her very muscular husband went in with her, armed with twin-cylinders (like me) plus an additional side-slung tank. The dives required considerable decompression stops. I asked if he carried the sling-tank for his lady wife but was told she didn’t need it. He did! What about my lightly breathing friend? Well, he could come back with half a tank of air when I was completely out but he couldn’t get through the night without waking up for a cigarette. He was a very heavy smoker. He also ended every dive with a humdinger of a headache. Am I saying that divers should take up smoking? Definitely not! New Zealander, Professor Simon Mitchell has investigated a subject that could be connected with the smoking phenomenon. He has studied carbon-dioxide retention in divers. Some people are able to retain a lot more carbon dioxide during the act of breathing than others and as you may know, it is the build-up of carbon dioxide that triggers our breathing reflex. It’s not the lack of oxygen but the raised levels of carbon dioxide that makes us have the desire to breathe. As I understand it, carbon-dioxide retainers breathe less. As a complete non-scientist, I wonder if heavy smokers with their constant lung exposure to carbon monoxide get a raised tolerance to carbon dioxide too, so that they can skip-breathe, leaving longer intervals between inhalations. Maybe their lung volumes have simply become very small due to the build-up of tar. Whatever the reason I’ve noticed they are more economic with their air supplies underwater. Cyclist Bradley Wiggins is supremely fit. After winning the exhausting 2172-mile Tour de France, a few weeks later he was competing in the London Olympics road race. How’s that for stamina? I read on the BBC website that he probably has huge left ventricles to his heart, which allows more oxygen-rich blood to be pumped to his muscles than we more ordinary folk. Chris Boardman, the Olympic Gold medalist in the Pursuit at the Barcelona Olympics in 1992, with whom I once dived a lot, had a resting heart-rate at his peak of around 38 bpm which indicates a large heart. I noticed he was an experienced diver who was able to be very relaxed on dives, with good technique and perfect neutral buoyancy, so that he didn’t rush through his air. A person’s endurance can be measured by taking a reading, which indicates how much oxygen is used every minute for each kilogram of body weight. It’s called a VO2 Max reading. A typical young male might have a VO2 Max of around 40 whereas a top cyclist might have a value of twice that, so that not only are they able to use more oxygen, they can also keep their muscles active for longer periods of time. Of course, cyclists have a never-ending air supply whereas for a diver it’s totally finite. I suggest it’s not clever to use less air than anyone else on a dive, although it may under certain circumstances be fortunate. I suggest it’s more intelligent to take sufficient gas with you for the dive in question and to manage that supply in such as way that you get back safely. Unlike running races and competitive cycling, it’s not a competition. A gas-integrated diving computer will help you manage your air supplies.