My friend's exH was EXACTLY the same. Became obsessed with the gym, came home one day with a massive tattoo across his back and, of course, my friend could do nothing right.
He was the biggest PITA about the gym. Posted stuff on Facebook to the effect that it was arrogant to let yourself go, and he was tearing himself down when he put on a little bit of weight etc.
And when he had the kids, he took them to the GYM as an outing - and a piece of equipment fell on one of the kids! It hurt them but not seriously, luckily. But still. What an absolute asshat.
A few shirt years after he left, he was diagnosed with a bad form of cancer, yet still couldn't stop drinking, and he was arrested for something recently. The kids don't see him much anymore.
I guess my friend wasn't the cause of all his problems, after all.
I absolutely think that all these men are/were having mid-life crises. They're SO similar! The tattoos, the gym, the turning against their spouse. The phrase "midlife crisis" doesn't seem to cover it. I think a complete mental breakdown would be more accurate.
I hope there's a special place in heaven for women whose husbands have left them and the children, especially when the children are very young. I think these men are complete cads, and not so long ago they'd have been seen as such, and shunned in society.