British Medical Journal: Repeated blows to the head sustained
during serial boxing or martial arts tournaments are linked to smaller
volumes of certain parts of the brain and slower processing speeds,
reveals research published online in the British Journal of Sports Medicine.
The
researchers base their findings on 224 professional fighters (131 mixed
martial arts fighters and 93 boxers), all of whom were taking part in
the Professional Fighters Brain Health Study (PFBHS), and 22 people with
no history of head trauma, but matched for age and educational
attainment.
All
of the PFBHS participants were athletes who were aged 18 to 44. Just
over half had not progressed beyond high school, while just over half
had at least some college level education.
The
amount of time they had spent as professional fighters ranged from 0 to
24 years, averaging out at 4 years. Similarly, the total number of
professional matches they had competed in ranged from 0 to 101,
averaging out at 10 a year.
All
participants underwent an MRI (magnetic resonance imaging) scan to
assess brain volume at the start of the study and then annually for four
years after that. Verbal memory, processing speed, fine motor skills
and reaction times were also tested to measure their brainpower.
The researchers calculated the Fight Exposure Score, or FES, which combines duration and intensity of fight career.
Generally,
the higher the score the smaller the volume, particularly of the
thalamus and the caudate, with each increase in FES linked to reductions
of 0.8% in both these structures.
The thalamus acts as a gateway to the cortex and can affect a wide range of neurological functions, say the researchers.
Smaller
volumes and a higher FES score were associated with slower brain
processing speeds, with an estimated 0.19% reduction in processing speed
per fight and a 2.1% reduction for each increase in FES.
Fighters with an FES score of 4 were 8.8% slower in processing speed than those with an FES score of 0.
Furthermore, higher FES scores were associated with a heightened risk of cognitive impairment.
Boxers
generally fared worse than martial arts combatants, irrespective of
their age. The volumes of their brain structures were smaller than those
of the martial arts combatants, and they were mentally slower.
“Perhaps
the most obvious explanation is that boxers get hit in the head more,”
suggest the authors. “In addition to trying to concuss (ie knock out)
their opponent, martial arts fighters can utilise other combat skills
such as wrestling and jiu jitsu to win their match by submission without
causing a concussion,” they add.
There
are several ways in which the thalamus and caudate could be vulnerable
to volume loss, they add, including the rotational movement of the head
as a result of punches delivered during a boxing match, for example.
“Not
only does it appear that differences in MRI volumetrics associated with
fight exposure can be detected in relatively young individuals, but
these differences occur in particular subcortical structures,” write the
authors.
They
go on to suggest that there do seem to be important indicators of brain
damage linked to repeated blows to the head, which could be used to
inform future regulations, while the FES could help to set criteria for
required neurological checks or retirement from the sport.