I have consistently found that a strange thing for either a man or woman to say. When I probe it, I always confess that I just don't think I have the perspective, detachment, or clarity to evaluate my own emotional/mental strength or independence. This observation & distinction tends to befuddle whoever I am speaking with. Smart folks, I suppose, huh?
Some "life coach" types teach people to say "I am strong, I am powerful" as a sort of daily affirmation, but it isn't the sort of thing you are supposed to repeat to others, even in print. Affirmations are for personal transformation - repeat them to others and they sound like false bravado. ;)