Wilt Chamberlain was an avid weight lifter who's strength and physique grew throughout his career. There were a couple of different stages in his physical progression:
(1) Wilt Chamberlain was the same size as a rookie Kevin Garnett when he was in college. 7-1, 220lbs. Stick thin. All limbs.
(2) In his early years in the NBA, Wilt Chamberlain bulked up to around 235-250lbs. Not to dissimilar to a David Robinson body type after a couple of years. Brain has gone blank for a good comparison prior to that, a slightly stronger Tyson Chandler type physique.
(3) By 1967, the year selected by Rebus I believe, Wilt Chamberlain was up to 270lbs or so. Wilt was one of the strongest players one would ever face by this point in his career.
(4) By his Lakers years, Wilt Chamberlain was up to 300+lbs. Shaq is the only player who could compare to Wilt in terms of size, length and strength at this point in Wilt's career. And vice versa. Wilt still had really good quickness and leaping ability too at this juncture in his career.
Wilt took terrific care of his body and was in much better shape than a lot of the older centers we've seen over the past 20 years or so. I don't think there has been anyone who has aged as well as Wilt did. Like this guy could still run up and down with a young Kareem and Kareem was one hell of an athlete in those days.
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As for the picture on the previous page, comparing Wilt to Shaq, Wilt's Harlem Globetrotter days were just before his first NBA season.