Those looking to produce a smart athlete should probably direct them to the swimming pool: the comparison, of a group of amateur football players, was made against a similar group of swimmers. The soccer players fared less well in tests of reaction time and flexibility of thinking, and the gulf between the two sets grew the more often a player had headed a ball.
Danielle Symons, who led the research at the University of Florida, said that during their careers footballers may head a ball thousands of times. Each ball weighs about 400 grams, or nearly a pound, and can travel at up to 120kph (75mph).
Modern balls are lighter than old leather ones, but that means that they travel faster - and the energy transferred by the ball to the person who heads it depends on the square of the velocity. Lighter, faster-moving balls thus pose a greater risk of brain damage, caused as the brain matter is abruptly accelerated during contact. Taken head-on, a top-speed football could pack as much energy as a prizefighter's punch.
The research, noted today in New Scientist magazine, tallies with a similar study carried out among professionals by the international footballing body FIFA in 1998, as well as work published in the Journal of the American Medical Association this year which said that amateurs showed "measurable evidence of chronic traumatic brain injury".
But the publication has come too late for Billy McPhail, a former Glasgow Celtic player who sued his former employers earlier this year, claiming at a benefits tribunal that repeatedly heading a heavy leather ball when he was playing in the 1950s had led to pre-senile dementia. His claim was turned down.
"If research like this had been in the public domain at the time of the case, the decision might not have gone against us," said Mr McPhail's solicitor, Tom Murray.
The Florida study found that the number of headers a player had made tallied well with how badly they fared in the tests - indicative that the findings were not simply an indicator that the footballers were "dimmer bulbs" to start with.
"Coaches should be encouraging better techniques. Some researchers believe that children shouldn't be heading a ball at all," Dr Symons said.Reuse content