Soccer players' trade-offs

Animal performance biologist Robbie Wilson has an unconventional take on life: when he watches a soccer match, instead of seeing sportsmen competing, he sees crayfish fighting. ‘Animals are fighting for the game of leaving their genes in the next generation, and on the sporting field it is the same sort of thing, just the currency is different’, explains the former semi-professional soccer player turned University of Queensland scientist. According to Wilson, animal performance biologists are very good at measuring maximum performance – speed, stamina and strength. However, quantifying other aspects of performance, such as fine motor control, is much trickier, and this was where Wilson's past caught up with him. Realising that he could accurately quantify the precise motor skills of soccer players, Wilson asked his former team, the University of Queensland Football Club, if he could turn their star players into lab rats to test his theories on how animals trade off characteristics – such as size and agility or speed and endurance – against each other (p. 545).

Designing 10 tasks that tested everything from the players' endurance and sprint performance to their ability to manipulate and control a soccer ball, Wilson turned up at the university's pre-season training field with his own soccer team of helpers, including Amanda Niehaus, Gwendolyn David, Andrew Hunter and Michelle Smith, ready to put 40 of the team's top athletes through their paces. ‘The guys were hypercompetitive’, Wilson recalls. ‘They wanted to know their results in each one of their tests immediately… so it was really difficult to say “No”’, he chuckles.

Then, after three gruelling days of recording each athlete's performance, Wilson was faced with the daunting task of sifting through the data to see whether he could find any trends in each individual's performance that might suggest that they were trading off one characteristic against another. But first he had to combat the problem of inter-individual variation. Essentially, everyone is different, and unless you take account of the natural variation of ability across a population, you might miss trade-offs that are swamped by the fact that some people are more or less talented than others. To overcome this problem, Wilson averaged out each of the athlete's performances so that all of the sportsmen were performing at the same standard, and when he did that, correlations began leaping out of the data.

‘It was very clear to see the trade-offs between speed and endurance,’ says Wilson, explaining that after standardising the results, the soccer players that performed best on the 1.5 km endurance run faired least well in the tests that required power, such as the long jump and performing squats. And when he compared each athlete's overall performance with their general ability across all of the tasks, there was a clear trade-off between generalisation and specialisation. ‘Individuals that were very good at a few specific tasks were not necessarily good when we averaged across all the other ones: you can't be fantastic at everything,’ he says, smiling.

So based on his experiences of working with soccer players, what does Wilson recommend that comparative physiologists do to take account of the natural variation in ability when looking for performance trade-offs in animal populations? He advises that, where possible, comparative physiologists should incorporate aspects of how an animal can control its body; they also need to measure more than just one or two aspects of an animal's performance. And, having ventured into the world of sports science and figured out how to quantify individual performance, Wilson is keen to adapt his approach to use it for talent spotting.