Also in this week's column:
What makes a good swimmer?
Asked by Carl Smiles of North York, Ontario, Canada
The best swimmers tend to be tall and thin with long arms, long legs, long feet, and long hands. The size of their hands gives them great "water grasp", and only a very small hand movement keeps them afloat.
They also have great strength, endurance, insulation against heat loss while in water below body temperature, thus better energy conservation, low resistance when in the water, and swimming stroke mechanics (for example, shoulder and elbow joints that move very well, etc).
Part of the reason why some people are better swimmers than others has to do with body density. The average person's body density is slightly less than that of water. Muscle has greater density than fat. Therefore, very muscular people tend to be poor at staying afloat. Bone has greater density than fat. Therefore, very skinny people tend to be poor at staying afloat.
Good buoyancy is not necessarily the most important factor in good swimming, but it certainly helps. For example, great competitive swimmers - tall, thin, and usually more muscular than average - tend to have greater body density than average and less buoyancy. Many would not float very well if they remained motionless in the water. Their much greater "water grasp" makes up for it.
The average woman contains a higher proportion of fat in her body than the average man, and the average man contains a higher proportion of muscle in his body than the average woman. Therefore, in general, women are better floaters than men.
However, buoyancy is only one factor in swimming. Nevertheless, compared with other competitive sports, the performance of women is closer to that of men in competitive swimming.
The density of salt water is slightly greater than that of fresh, so the body has greater buoyancy in salt water. All other factors being equal, you can swim faster in salt water than in fresh water. This is also why you can easily float in the Dead Sea due to its very high salt content.
A person can swim faster in calm rather than turbulent water. In competitive swimming, the inside lanes are faster due to the fact that the lanes closer to the sides of the pool tend to be more turbulent from the waves hitting the sides of the pool and "washing" back.
Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to firstname.lastname@example.org