Biology Question #1937

Robin, a 45 year old male from Brighton asks on February 26, 2004,

How is it that some people can 'float' while others seem unable to? In the sea I can quite happily float on my back for ages without even moving, however when my partner tries it she starts to sink! Is it down to body 'density' or just technique?

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The answer

Michael Poling answered on March 10, 2004

Three things affect your buoyancy. The amount of fat tissue in the body (fat floats), the amount of lean muscle tissue (muscle sinks) and the amount of air you can hold in your lungs (the bigger the balloon, the more it floats). People with more fat in their body float easier (not just those love-handles...we have fat all through our tissues, so you don't have to LOOK fat), but others may have lots of fat, yet sink. Why? They also have lots of lean muscle and dense bone too. Think of a life preserver. If a 200 pound man uses a child's life preserver, he'd likely drown, right? That's because he's got too much weight for the life preserver to hold. Same idea with fat might hold you up, but not if you have too much muscle and bone.

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