Buoyancy depends on density: the denser you are, the less buoyant you
are. Fat is less dense than blood, muscle, or bone, so the higher the
proportion of fat in a body, the more buoyant it is.
Of course, another factor makes an even bigger difference: air. Air is
much less dense even than fat, so how much air you hold in your lungs
makes a big difference to your buoyancy.
Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
Just for fun, but also to make a serious point, it is possible to carry out a ‘children’s science experiment’ to investigate how buoyant fat and air are in water. If you take a small glass and half fill it with water you can pour in a small amount of cooking oil to represent fat and watch it float on top of the water. If you take a straw, place it in the water and blow through it, you can see air bubbles rising up through the water and oil. This is because air is much less dense than water and is therefore extremely buoyant.
Think about yourself. Approximately 60% of you is water. What about the rest. Fat, bone, air (let’s simplify the respiratory gasses) muscle, blood, other body tissues.
Fat helps you to float. What else helps that you have control over?
The amount of air in your lungs, the density of your muscle tissue (less dense when relaxed) and the shape your body makes in the water.
A big hinderance when you are learning to swim is worrying too much about getting it right. You should ask yourself what you are trying to achieve and if you mange to do it calmly without causing strain to yourself then you are doing it right, for you at this time.
The more I teach swimming, the more I realise that the biggest barrier to learning that people have is their anxiety. Getting people to acknowledge this fact is a step in the right direction, but it isn’t a solution to the problem. It is vitally important as a learner to realise that your relationship with the water changes dramatically over time. As long a you are prepared to spend time in the water and feel in control, ie only doing things that you are comfortable with, you will become more relaxed in water. There is no quick fix.
Don’t believe anyone who tells you there is only one way…find ways for yourself.
I was taught to always exhale when my face is in the water and never hold my breath and this is something I generally advocate, however there are times when you are investigating your relationship with water (e.g buoyancy) when filing your lungs with air and holding your breath can give you real insight. I realised only yesterday that my usually sinking legs will stay near to the surface if I hold my breath with my lungs full, as my center of buoyancy changes.
It is important to think about how you use parts of your body to move you through the water,but it is easy to get too hung up on trying to follow the instructions in your head. If you can stay relaxed and playfully try different ways of moving your arms and legs you can learn a lot more about propelling yourself through the water.