Marciano and Frazier due to their legendary stamina and punching power, I think they had less genetics working in their favor compared to say Ali or Foreman Patterson, and I'm gonna say Tyson too, Cus wasn't doing anything "new school" with him, and that's right on the line of Tyson's peak, obviously he had genetics in his corner
Because Spinks was the model for future strength and conditioning by elite boxers. That's when things started to change.
Spinks train to fight Holmes is model for weight gain. yes my point: if Spinks brought new method (I am not sure is true. but you believe) you can say his era was other boxers all ' old school "" Tyson is good example for thread. but ok you has barred from him being including! in that case is Frazier! most brutal= Beau Jack!
Jim Jeffries. That guy was jacked. His physique was next level and he went 23 rounds with Corbett. Top level heavyweights even 30 years later couldn't duplicate his look and functionality.
