Mike's Notes on Personal Buoyancy.

A lot of people are visiting this site, looking for information about personal buoyancy. I hope these notes will be of help.

In order to understand Personal Buoyancy, we need to think about the way our bodies are constructed. The main components of the human body are bone, muscle, fluids, fat and air cavities. Bone density varies throughout life, but is normally the densest component of the body, reaching its maximum in early adulthood, then decreasing gradually with age. Muscle is also fairly heavy and tends to sink in fresh water. Body fluids are only very slightly denser than fresh water. Fat (between 15% & 30% of body mass) is positively buoyant in water. Air cavities (primarily the lungs) account for most of the body's buoyancy. An adult's lungs can hold around 5 litres of air (10% more than an Imperial gallon or about 30% more than an American gallon) providing 5 kg of buoyancy (about 11 lbs.) So the amount of air in the lungs makes a lot of difference - the difference between floating and sinking in the case of an average adult male. Personal buoyancy is always measured with the lungs full of air.

Fred Lanoue found individual personal buoyancy ranging from 7 lbs. positive (floaters) to more than 5 lbs. negative (sinkers). When he tested young African-American males at Morehouse College he found that 30% had negative buoyancy - a much greater percentage than among the white students at Georgia Tech. This result is now regarded as controversial. It seems unlikely that he would have deliberately produced misleading results, but racial origin is unlikely to have been the only difference between the two groups of students that would have an influence on personal buoyancy.
And we have now seen Cullen Jones, a member of the winning USA 4 x 100 Freestyle Relay Team, smash the stereotype by winning a Gold Medal in the 2008 Beijing Olympic Games. You will find lots of information about him with a browser search of the Web.
I would be very interested to hear from anyone who was at Morehouse in the 50s or 60s.

Fred Lanoue's measurements were made at a time when people were generally leaner than they are now and because he was mainly working with young adult males, he was teaching Drownproofing to the least buoyant group within the community. Broadly speaking, women and children tend to be more buoyant than adult males. Adult buoyancy tends to increase with age. Athletes are less buoyant than the general population. It is difficult to say how important personal buoyancy is in swimming. The fastest sprint swimmers are young adult males. They often have greater than average lung capacity.

Negative buoyancy tends to be a disadvantage, because the swimmer has to divert some of his energy into remaining at the surface. Distance swimmers who go in for cold water events such as the English Channel, are normally very buoyant, carrying a layer of body fat ranging from 6mm. to more than 15mm. but the benefit they gain from this is more to do with insulation from cold, rather than the increased ability to float. Water conducts heat away from the body 25 times faster than air.

Once the technique of swimming has been mastered, a negatively buoyant person will be able to adjust his style to compensate for the tendency to sink, but the early stages of learning are likely to be more difficult, So there is a good argument for learning young – or trying again when you are of more mature years.

If you are negatively buoyant (a sinker) here are a few ideas that might help.

Learn to swim in a wetsuit. These are made of neoprene rubber containing millions of tiny bubbles of nitrogen, so they provide extra buoyancy as well as insulation. A wetsuit made of thicker material will weigh more in air, but it will provide more buoyancy in water.

Salt water gives more buoyancy - around 4 or 5 lbs. for the average male. I suspect that almost everyone would be positively buoyant in the sea. A warm salt water pool is a great place to learn to swim.

If you workout with weights, concentrate on exercises that will expand your ribcage and increase your lung capacity.

Whatever you have read or heard anywhere else, NEVER exhale under water! Always wait until your head is coming out of the water before you let go of your breath. Remember, air accounts for most of your buoyancy.

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Copyright Mike Kearney, 2008.
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