Mike had back and neck issues. If you watch a few ring entrances and pre fight introductions he would often twist his neck, almost a twitch of sorts. Esp if you watch the Mike Spinks fight when mike is entering the ring through the crowd. read more
There’s a couple of other Tyson photos below you can compare, and also a photo of Anthony Joshua (on the left), if you look at his abs you’ll see what I mean about how genetics can cause your musculature to be asymmetrical. read more