Hold your breath part1
How Long Can You Really Hold Your Breath-Part1?
First of all, to all those of you who are new to freediving, remember that any sort of breath-hold activity is potentially dangerous. Never ever do any sort of breath-hold activity in water without the supervision of an experienced freediver. If you don't know any freedivers, have a look at our freedive school directory here or google search for your local freediving club. You won't regret it! One of the things I usually end up telling people who ask about freediving, thinking that we must be a bit mad to do what we do, is that every fit and healthy human can hold their breath for at least 4 minutes and dive to 30m. I'll also often tell them about the world record for static Apnea, currently held, of course, by Serbian Branco Petrovic.
I'm reminded of the amazing breath-holding ability of the human body and mind every time I come up from a static, blue in the face and gasping, another couple of minutes short of my best, and I can't help but think I must be missing something. So I thought I'd look at a way to work out roughly how big a static a person should, physiologically speaking, be able to manage. I've got to warn you, the results of my scurrying through cyberspace and racking my own tortured, oxygen starved brain are...let's say...involved... so if you want to cut to the chase, click here to skip to the (surely by now) world famous Freedive-Earth Maximum Breath-hold Calculator, and instructions on how to use it or, if you're curious...read on.
It's all in the Body
Putting psychological aspects aside for a minute, Static Apnea is basically about how much oxygen you can take down with you, and how long you can make it last. So we're going to look at how different aspects of physiology play their part. The minimum amount of oxygen that the body consumes each minute is called the Basal Metaboloic Rate (BMR) and, for pretty much anyone, it can't get a lot lower than 250mls a minute (ml/min). That's the amount of oxygen it takes to keep your heart beating and your ions in all the right places in your cells, so without it, you wouldn't last long. You'll use more oxygen if you're not relaxed, so the aim of relaxation is to reduce the metabolic rate as close to the BMR as possible, meaning that the oxygen you take down with you will last longer. It's important to say at the outset (and we'll come back to it again before the end) that this model doesn't take into account the effect of the dive reflex on BMR, so it may be that you can use oxygen more efficiently than this, but the aim here is just to look at how we store oxygen, and how we might be able to store more of it.
So... how much oxygen can we cram in?
Oxygen is basically carried in the body in 3 compartments: Lungs, Blood and Muscle. Together they make up the Total Oxygen Carrying Capacity. We'll look at each of these in more detail in the following parts but, as an overview: A large (though sometimes not the largest) reservoir of oxygen in the body is obviously the lungs. 21% of your final breath is oxygen, so, if you take, say, a litre more air, you're getting 210mls more oxygen, or roughly another minute of breath-hold, all other things being equal.
Blood is a little more complicated: Most of the oxygen (around 98.5%) in blood is bound to haemoglobin, with the remaining amount dissolved directly in the blood. The total amount of oxygen that the blood can carry depends on the volume of blood and the concentration of haemoglobin within it. That's one of the reasons why hydration and a diet rich in iron are important for holding your breath. Perhaps the most neglected part of our diving physiology is the role of myoglobin, found in muscle tissues. Myoglobin is a pigment structurally similar to haemoglobin but with a much higher affinity for oxygen at lower partial pressures. The accepted role for it in the human body is as a kind of relay between the blood and tissues with a high demand for oxygen, like the heart. For habitual diving mammals like seals (the elephant seal has been recorded on dives as long as 2 hours on an exhale!) more than 50% of the total oxygen carrying capacity comes from myoglobin, for humans it's a lot less but depends in part of the amount of muscle that you have. In the parts of this series that follow we're going to break down each compartment to see how it works in more detail, then use the information to build up a model of the whole.
The next part (all about the lungs) will be published this time next week, so tune in then for more detail on that. Don't forget, too, that you can access the Breath-hold calculator and work out your own theoretical maximum here.