Engineers build impact testing device to analyse sports fields

Sports engineers at Cranfield University have tested a device that can measure the mechanical properties of natural turf in an effort to better understand athlete–surface interactions.

Greater knowledge of these interactions could help to prevent injuries and aid athlete performance, the researchers claim.

Dissipation of impacting energy and reduction of loads returned to athletes is regarded as important for preventing injuries, while stiffness and energy return from sports surfaces allows athletes to perform movements more efficiently — with a compromise often sought between the two.

‘One of the main issues is that the new modern, elite-level surfaces are made of sand and their properties are a lot stiffer compared with the average Sunday kick-about pitch,’ said Dr Matt Caple of Cranfield, who collaborated on the recent project. ‘With this device we’re trying to assess how the surface reacts to stresses applicable to athletes, in terms of how much it compresses and the energy it absorbs.’

After banning artificial pitches in the early 1990s, football’s governing body FIFA has recently passed a motion permitting them in competitive matches — but with strict requirements. It has developed an ‘artificial athlete’ testing device to make sure the pitch surfaces adhere to certain mechanical parameters.

Caple, however, noted that an equivalent system is currently lacking for natural turfs, which require a different approach in terms of measurement.

His solution was a vertical dynamic impact-testing device (DST) consisting of a compressed air-driven ram that vertically impacts a studded test foot onto the surface, using data from biomechanical studies.

It was originally built for assessing horse racing but was found to be unsuitable and another Cranfield-developed device, the GoingStick, was eventually developed and commercially adopted for this purpose.

‘While the GoingStick measures the actual strength of the surface, the DST measures energy absorption, so we’ve taken this device, developed it and put more components on it, then modelled it against a biomechanical study of players running on turf.’

Caple’s team has just presented data obtained from the DST on professional rugby and football pitch-testing studies over two seasons.

‘What we found was that sand surfaces are more consistent across the season compared with more clay or silt-dominated soils. Because the infiltration rate of the soil [is lower], the strength isn’t as reliant upon moisture content so it doesn’t deform as much when it’s loaded.’

Caple is hoping to perform further studies on his DST and perhaps commercialise it for advising on the installation of new turfs or re-surfacing.