Previous studies of boxers have reported that the frequency and duration of fighting seems to be associated with cognitive or neurologic problems. This study included data from the Professional Fighters Brain Health Study (PFBHS), a longitudinal cohort of boxers and mixed martial arts fighters designed to understand the effects of repeated blows over time.

Participants were at least 18 years of age and were licensed to fight professionally in either boxing or mixed martial arts. A control group was recruited, matched for age and education, with no history of head trauma. Participants were seen for baseline evaluation and on an annual basis thereafter over the next four years. Baseline demographics and cognitive function were determined for all subjects. A high-resolution T1 weighted anatomical MRI was obtained with volumes of the hippocampus and amygdala, as well as the subcortical gray matter, calculated. Fighting exposure was determined by professional records.

Data were collected for 224 male fighters, including 93 boxers and 131 mixed martial artists, as well as 22 controls. The number of years of professional fighting ranged from zero to 24, with a mean of four years. Increased exposure, as measured by the number of professional fights or years of professional fighting, was associated with lower brain structure volumes, particularly subcortical structures. The most consistent relationships between exposure variables and brain volume involved the thalamus and caudate. Among the cognitive domains, only processing speed was related to volume of exposure. A significant relationship was seen between the number of professional fights and speed of processing (P＝0.041), with an estimated 0.19% reduction in processing speed per fight.

This study of professional boxers and mixed martial artists found that increased exposure is associated with lower brain volume, particularly in the thalamus and caudate, and with a decrease in processing speed.