Why are athletes beating world records?

London - What is the key to athletes beating their own records, consistently. A "performance improvement index", based on a comparision of the relative improvement of top  athletes over the last 100 years, explains why.

Steve Haake, director of the Centre for Sports Engineering at Sheffield Hallam University, UK, who has developed the 'index', said it shows how men's 100-metre sprint is increasing at a  time when those of other events, such as javelin and swimming, have plateaued or decreased.

"One way of finding out how exactly technology affects sporting performance is to examine the physics involved. We can then try to quantify the effect of technology on sporting events - and  find out whether it really is all about the equipment," says Haake, the journal Physics World reports.

Haake also describes the step-change in the men's 100 m in the mid-1970s with the introduction of fully automated timing. In swimming, an unprecedented 25 and 47 world records were broken in 2008 and 2009, respectively, with tight-fitting, full-body swimsuits seen as the main reason, according to a Sheffield statement.

The performance of javelin throwers, for example, was improving drastically up until the mid-1980s, to a point where officials were concerned for crowd safety.

At the time, javelins would float to the ground and land flat, meaning it was very hard to tell where the tip had hit the ground.

As such, the International Association of Athletics Federations (IAAF) changed the specifications of the javelin itself, moving its centre of mass towards the tip by four cm and so forcing the

javelin to land on its tip, thus reducing throwing distances by about nine metres.

The swimsuits, which have now been banned by swimming's ruling body (FINA), were relatively tight and reduced the cross-sectional area of the body by pulling it into a more cylindrical

shape, thus reducing drag. They were made from polyurethane, which also affected the way the water flowed over the body.