WHEN swimmer Rebecca Adlington from Great Britain (pictured) won the 800-metres freestyle Olympic final last week, she finished in a world-record time of 8 minutes, 14.10 seconds, wiping more than 2 seconds off the previous record, which had stood for 19 years.
A day later, America鈥檚 Michael Phelps won a record eighth gold medal in a single games, having smashed seven world records along the way. In total, 25 world speed records have been broken in the pool since the Beijing Olympics began on 8 August. By contrast, just eight world records were set by the pool swimmers in Athens in 2004. Why the big difference?
The answer, according to Brent Rushall, an expert in exercise and nutritional sciences at San Diego State University, may lie in the depth of the Beijing pool. It is 3 metres compared with standard pools such as the one used in Athens, which are only 2 metres.
Advertisement
A swimmer鈥檚 movement through water causes two waves to form around the body: a bow wave at the front of the body, which moves outward and downward, and a stern wave at the rear. This process transfers energy to the water and is responsible for much of the drag that impedes a swimmer鈥檚 progress. Patterns of reflected waves depend on the swimmer鈥檚 velocity and the shape of the pool.
鈥淭he downward portion of the bow wave hits the bottom and reflects back toward the surface,鈥� explains Rushall. If this returning wave coincides with the stern wave or hits the swimmer, this slows them down. 鈥淭hat is why shallow pools are 鈥榮low鈥�.鈥�
In contrast, if the pool is deep, the swimmer will have moved further by the time the bow wave has reflected back upwards and so less additional resistance occurs, if any.
The Beijing Water Cube pool has other features designed to reduce swimming resistance, such as an extra lane at each edge of the pool to reduce reflections from the side. The Athens pool had a similar design, however.
The depth of the pool has raised questions about the validity of the Beijing records. But there are other official pools which are 3 metres deep or more, says Rushall. 鈥淭he current spate of swimming records is fair and valid.鈥�
