You've gotten some good advice, and some not so great advice. I only have a few minutes, and I will expand later.
I am sorry you are depressed....and it's a good idea.
But basically, you want a slow takeaway of what you do for her. Not in the manner Strong has described. And if you give an ultimatum, you will most likely have to live with the consequences of that. Plus...it will add to her 'contempt'.
If your goal is to save your marriage, stick with advice that has been proven successful to that end....
"I have been working out and running for almost 3 years now and I feel like I am physically in good shape. I don't think I am ugly or anything like that, but I do not understand why my wife does not find me attractive anymore. I am in better shape now than I was when we met...but that ties into her thinking I am less of a man now I suppose."
It has more to do with your PATTERNS OF INTERACTION.
More later.
sg Love is PATIENT, love is KIND, LOVE never fails / DB since 2001
