When Lewis didn't train, cardio has a lot to do with your chin. Look how Lewis did against Tua's punches when they landed, Vitali Klitschko's, Mike Tyson's early on. His chin was more htan good enough, but stylistically he would have never fought FOreman with such reckless abandon as he did against Rahman and the first McCall fight(which shouldn't have been stopped).
Foreman was almost ko'ed by Ron Lyle, and Ali knocked him out, neither of them could hit as hard as Lewis.
My point is that Foreman's advantages were in his size and power when he was younger. He developped more boxing skills later in his career, but in his youth he was a pretty rudimentary fighter.
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