That's true. Bodybuilders nowadays - the competitive ones - are eyepoppingly huge. Some of these guys look inhuman.
Muscular heavyweights with low body fat are not necessarily what I'd think of as "bodybuilder types".
yeah true body builders today are simply too big, slow and bulky to be good boxers. plus the stamina issue from dancing around with all that muscle in the ring.
As far as Bodybuilding genetics Norton, Weaver,Dempsey, Williams and Holyfield come to mind, small waist and wide shoulders and naturally muscular physique. These are the athletes Foreman, Jefferies, Louis and Morrison were built for strength with thick waists, forearms, calves a good DE/LB in the NFL. Tyson, Frazier, Chuvalo, Marciano are built for strength with big legs, thick waists short arms the prototypical power running back. And built for power lifting with their short stature and and center of gravity
Bobby Stewart did a fascinating piece on Tyson about 15 years ago in 'The Ring'. He said he saw Tyson's friends at the young offenders institute he was in bet him he couldn't bench 250 pounds, and that Tyson went ahead and did 10 reps. Will never forget it.
Ken Norton actually criticized Shavers for lifting weights while broadcasting for NBC during Earnie's ten round stoppage of Tiger Williams. Mike Weaver has made it very clear that his physique was "a gift." Hercules (a nickname his friend Norton gave him) weighed 202 for his June 1979 challenge of Holmes, 234 for his November 2000 rematch with Larry, but with the 32 pound increase in weight, Mike's physique stayed basically the same at age 49. (Holmes was also essentially built the same at 255 as he was at 203 for Rodney Bobick on the Manila under-card, rather pear shaped.) Weaver actually did experiment with weights during the early 1980's, and wound up injuring himself. Max Baer's body also pretty much looked the same at 203 for Levinski II and Schmeling as he did at 220 for Nova II, and during his late 40's when posing in boxing gear beside his sons. He was just blessed with that long clavicle which guaranteed a tapered waist. Jumbo Cummings was probably the definitive weight trained bodybuilder of the early 1980's, having gotten into muscular development during over a dozen years in jail through the 1970's. He failed to physically overpower Joe Frazier the way Foreman had, but came w/in seconds of an opening round KO of undefeated Frank Bruno in his career finale. Under Mackie Shilstone's guidance, Mike Spinks beefed himself up with weights from 170 for David Sears to 205 for the Holmes rematch a year later, and finally just over 212 for Tyson (who weighed just six pounds more), but the Jinx retained pretty much the same sunken chested physique over that 42 pound weight gain, and has retained the same lanky frame in retirement. (Most of his visible increase in muscle mass was evident in his legs. He was always rather self conscious about how skinny they were, but began wearing shorts rather than sweats while training in the gym as a heavyweight, no longer embarrassed about displaying them.) George Foreman did not get into weight training until his second career, and published an interesting anecdote in a Parade Magazine fitness column after he regained the title. During his hiatus, he went to a gym specifically to try getting rid of a double chin with targeted exercises to no avail. But after his comeback, with muscle building, he happened to notice one day that his double chin had disappeared. George's legs were surprisingly thin during his first career (some reports have his calves measuring just 13 inches), but transformed into tree trunks by his 40s (calves allegedly increased to 20 inches).
No one's mentioned Ron Lyle, after seeing the Foreman - Lyle fight not too long ago, and them mentioning Lyle had done time in prison, it would surprise me if he never lifted weights.
Not all boxers in prison did. James Scott had a heavyweight's upper body, but he did an insane amount of sit-ups and push-ups in his cell to go along with the hour of running in the Rahway prison yard while outdoors.
I saw mma fighter/bodybuilder Bob Sapp fight on YouTube and he hits about as hard as a middleweight boxer. He must weigh near 300 pounds.