I’d speculate that it’s blood flow related due to varying degrees of cardiomyopathy and heart failure. I’ve lost a bit of size and strength in my right arm due to blockage of coronary arteries and damage to the heart muscles-but I’m not that far along, or that big in the first place, so it isnt very noticeable, except that being right arm dominant, it used to be a tad bigger and a couple reps stronger than the left.
The guy in the vid is on the right track, but lookin at some confusing symptoms, as the distended abdomen does occur in diabetics, which is also often accompanied by, and a cause of heart failure.
The thing is, a typical heart failure and/or diabetic patient is not really lean and jacked like these guys often are, and no one would really look at them and think “heart failure”.
So that’s my brosplanation based on my newfound favorite subject. Weak pumps can’t push as much as far, so the extremities suffer.