Most people just assume that Muhammad Ali, the self-proclaimed “Greatest of all Time,” suffers from Parkinson’s Disease because of his years taking head shots in the boxing ring. However, Ali’s personal physician, Dr. Abraham Lieberman, said during an interview with BBC Radio Five Live’s Sportsweek programme, that there is no way to know for sure why Ali got Parkinson’s Disease 30 years ago.

Lieberman, who is also the Medical Director of the Muhammad Ali Parkinson Centre, doesn’t think that it’s possible to conclude with certainty that Ali’s boxing career caused Parkinson’s. “People ask me about this and I tell them: look at George Foreman. He boxed longer than Muhammad did, took many more blows to the head and he’s on television selling his cookware,” Lieberman said. “I think that he (Ali) has typical Parkinson’s Disease. Did the boxing contribute? I don’t know. It may have.”

Parkinson’s Disease affects nerve cells in the brain. Its symptoms include tremors, muscle rigidity, changes in speech, and difficulty walking. Although Ali has suffered from the disease since the mid 1980s, Lieberman said that the 72-year-old has only had issues walking over the past ten years. “His course has been more that of typical Parkinson’s Disease. If you look at the MRI of his brain it looks pretty good but it’s very difficult to factor in what sort of role did boxing play.”

If you think that Parkinson’s has marred Ali’s retirement life, according to Lieberman, you would be wrong. “He’s in good spirits, he has some trouble walking but overall for having had Parkinson’s for 30 years, he’s doing okay.”

The boxing world recently celebrated the 40th Anniversary of The Rumble in the Jungle. The boxing match, which took place in Zaire (currently Democratic Republic of the Congo) is often considered one the greatest sporting events of the 20th century. The epic match pitted heavyweight champ George Foreman against Ali, who had lost his world championship title, because he refused to enter the draft in 1967.

By 1974, at 32, it seemed like Ali was washed up and had no chance of beating the 25-year-old Foreman. However, eight rounds into the match, Ali and his famous rope-a-dope strategy knocked out Foreman for one of the biggest upsets in sports history.

40 years ago today, @MuhammadAli defeated @GeorgeForeman in the Rumble in the Jungle. pic.twitter.com/QVcD5J3eYj

— Muhammad Ali (@MuhammadAli) October 30, 2014

Ali’s personality was always larger than life. He was the talker, the poet, the man with the hype. His daughter Hana says that her dad still has that wit about him, even today, “The last time I talked to my Dad, he was joking again about making a comeback,” said Hana. “He said, ‘I’m going to take my title back for the fourth time.’ Whenever I hear him joking like that, it makes me feel good. He’s still in there.”