According to a new study from Arizona State University, Muhammad Ali’s speaking ability began to decline as soon as age 30 because of boxing.

“Ali’s articulation started to become less precise in the mid-1970s, when he was between 30 and 35 years old, almost certainly as a result of blows to the head suffered in the ring. The study suggests that changes in the quality of speech can be important early markers of neurological damage or disease,” reports the Wall Street Journal.

The study also found that Ali experienced a 26 percent drop in speaking rate between ages 25 and 40. Most adults see no drop at all.

Neurological research such as this has yet to have an impact on boxing as on other sports, such as football. However, evidence that Ali suffered from CTE as a result of boxing could change that.

Although that specifically isn’t the conclusion being presented in the study, it’s worth noting speaking struggles are a symptom of the disease.

Ali is also just one boxer of thousands. But if this study holds up when examining others, it could ultimately prove a link between boxing and the deterioration of speech. It’s certainly plausible that such a link exists given the violent nature of the sport.