Loughborough University researchers have published what they consider to be a seminal paper on the neurological impacts of heading in football.
The key results of the study, funded by the FA and conducted independently, were the identification of “distinctive pressure waves” in the frontal brain region when the head meets the ball. The researchers say this was “previously unreported” and provides some explanation for the mechanics — and potential neurological consequences — of performing headers.
“We’ve measured for the first time a feature of the collision, which has always been there, but we’ve not been using the right sensors to record it,” explains Professor Andy Harland to The Athletic from an office at the university campus near Leicester in the English Midlands.
“Something very consistent, very repeatable, is happening every time a ball collides with something. That generates this pressure wave, which, if you’ve made a header, progresses into the head,” he says.
Dr Ieuan Phillips, lead researcher on the paper and a PhD graduate at Loughborough, says that they have “described the nature of the energy going into the brain”.
He adds that the pressure wave is a “really distinctive form of energy transfer” which has been “well-established” as a cause of brain injuries in other contexts, such as low-level military blasts. Harland, who has a background in medical ultrasound, knows that pressure waves are used to remove kidney stones.
Because none of the Loughborough researchers have applied medical backgrounds — “We’re not neuroscientists,” Harland says — they stop short of drawing definitive, causal links between these pressure waves and neurodegenerative diseases. That is not because they think there is no link, but because it needs experts in neuroscience to prove one exists.
A study published in 2023, led by the University of Nottingham and commissioned by the FA and the Professional Footballers’ Association, showed that medically diagnosed dementia and other neurodegenerative diseases were three times more prevalent among retired professional footballers than in the general population.
“We can’t say exactly what the damage is or how it’s working, but we know from the laws of physics it’s something we should be aware of; it’s an energy which is being put into the head,” Harland adds.
Another standout point from the paper, published in The Journal of Sports Engineering and Technology, was that leather-style footballs from the 20th century produced “peak pressures” impact forces four times higher when wet — a result they called “substantial”.
Balls with more modern designs — specifically the kind that are synthetic machine-stitched and have been used at elite levels of the game since 2016 — returned the least severe impact forces and were more water-resistant.
Ninety per cent of the energy transfer was found to occur within the first 500 microseconds (0.0005 seconds) of contact with the head.
“The thing that is governing that energy right at that point in the collision is those material constructions within the shell of the balls,” Phillips says.
“We tested different balls from throughout the last century, including leather ones, hand-stitched synthetic and the modern stitchless balls. We see rather large differences between: up to 55 times in terms of the energy transfer (between older and newer balls) purely based on shell materials and construction — which is obviously quite a big finding.”
Across the 20 footballs tested, 90 per cent of the energy transfer to the head was found to happen within the first 500 microseconds (0.0005 seconds) of contact.
Seven subcategories of ball were considered, based on their design, manufacturing and the era in which they were/are used. A total of 430 “collisions” were recorded across three different trials, to mimic speeds from corner kicks, aerial passes and shots, in both wet and dry conditions.
They created a half-skull based on measurements provided by MRI data from the Institute of Science Tokyo, which had been designed to represent the average (50th percentile) male player. An embedded sensor measured the pressure waves, and no meaningful changes were identified when they made adjustments to the skull geometry.
“We developed a pretty bespoke set of apparatus in the lab to do it in a very controlled, realistic sense,” says Phillips. Loughborough is widely considered the leading sports university in the UK and has particular long-standing expertise in ball testing — Phillips’ PhD focused on potential subconcussive brain injuries from heading.
Harland cites Professor Paul Lepper, his PhD supervisor from the 1990s and an underwater acoustician, as instrumental in the four-strong multidisciplinary research team. Dr Sean Mitchell, also involved, provided important mathematical and theoretical insight. “I can’t imagine another combination of people that would have been able to put these jigsaw pieces together,” Harland says proudly.
He and Phillips are also grateful to the FA, not just for providing a grant to fund the research but also for its trust and interest. They met FA staff twice yearly while the study was ongoing to provide updates. “It’s fair to say we’ve taken them on a journey,” Harland adds.