It was said that when Foreman made his comeback. He used to use 100lb dumbells and punch with them during his training routine :bbb. That's impressive.
I wouldn't put anything past Foreman. His strength was incredible. He probably would have made a good strongman competitor if he had trained purely for strength rather than for fighting.
Well, he did pull around a truck using a yolk around his neck, and he did lift that steer over his head, but this sounds hard to believe. Many he could throw a few punches that way, but not anything sustained.
I think this is a Paul Bunyanesque story 20-25 would be big for a mortal man. Shoulders are an Achilles heal, please forgive me, jointwise. I wouldn't be at all surprised to hear that he did weighted shadow boxing, but something reasonable. I recall Foreman talking about that during his first career that he would cut water before fights which is freakin' insanity. I think George 2.0 updated his training philosophy the 2nd, arguably his 3rd time around.
One day they will tell the tale of Big George lifting a herd of cattle to show how strong he was after losing to Ali. https://www.google.com/search?q=George+Foreman+lifting+a+calf&client=tablet-android-samsung&prmd=sivn&source=lnms&tbm=isch&sa=X&ved=0CAgQ_AUoAmoVChMIq_n9v8OHyQIVjCqICh1cWAy1#imgrc=awELCoaZRg6hnM%3A