Alberto Minetti is fascinated by machines that improve human physical performance. He describes the bicycle as a `marvellous invention' which increased man's top terrestrial speed by approximately 300% at the energetic cost of a light jog. But the story isn't so impressive in water. The only tools that humans have developed to boost swimming performance are fins. Bikes increase muscle efficiency by taking the legwork out of supporting our own body weight. But a swimmer's weight is already supported by the water, so how do the fins benefit their performance? Minetti and his team began scrutinising every detail of swimmer's leg strokes as they swam with and without fins(p. 2665) and discovered that the appendages increase the size of the propulsive jet of water that pushes a swimmer forwards with less wasted energy.
Compared with air, water is a dense and viscous medium. With every kick, a swimmer...
