One guy is on roids, one guy isn't. That being said, Wilder has Russell Jr's legs, and Russell Jr. has the head size of a guy Wilder's height.
Wilder vs Joshua vs Klitschko comparison: Height: 6'6'' 1/2 (6'7'') - 6'6'' - 6'6'' Weight: 228 3/4 lbs - 244 lbs - 245 3/4 lbs Neck: 18'' - 18'' - 19'' Chest: 42'' - 41,7''(47'') - 47'' Bicep: 16'' - 17,3''(19'') - 18'' Waist: 36'' - 34.6''(36'') - 34 Thigh: 18'' - 26''(27'') - 22'' Calf: 14'' - 16.5''(17'') - 17'' Source's: http://i.dailymail.co.uk/i/pix/2011/07/01/article-2010429-0CD3B4A300000578-818_634x615.jpg http://roundbyroundboxing.com/wp-content/uploads/2016/04/Martin-vs.-Joshua-Tale-of-the-Tape.png http://fightfan.com/wp-content/uploads/2015/01/1-17TALEOFTHETAPE.png https://www.flickr.com/photos/sunshinetrue/sets/72157603044301126/ Wilder's upper body seems a little bit underrated actually(!)