The after effects of fighting into 1981 when he was past his best shows the tolls of what came later for Ali. The battering that he took from Larry Holmes, one of the most underrated Heavyweight champs of all time for 10 rounds was horrific. Then the Berbick fight a year later. Another aspect that isn't discussed is that Muhammad while having great head movement and ability to move back from shots, prided himself on taking his opponents body shots over and over and over again. The 3 fights with Frazier culiminating in the Thrilla, Ali took SEVERE body assault from Joe. Joe was a body snatcher, breaking fighters down.
The Foreman fight with the rope a dope, Foreman is one of biggest 1 punch heavyhanded boxers of all time. Doing the rope a dope, again he took a battering to the body. He fought a who's who, The Bear Sonny Liston, Earnie Shavers (one of the hardest punching light heavyweights ever who moved up), Ken Norton, Ron Lyle, Jimmy Young, George Chuvalo (greatest chin of all time IMO), Henry Cooper, Bob Foster (Another hard puncher and all timer), and on and on.
Most list Ali as the Greatest Heavyweight of all time, others list Joe Lewis. I lean a little bit more on the side of Joe Lewis, more because of the meaning of what Lewis-Schemling 1 and 2 meant to the world at the time and the aftermath. Ali is 1B IMO but it makes no difference since he transcended his era and sports at the time as still to this day. Very sad day for me. RIP Champ!