I used to do way too much cardio. I was a big proponant of doing as much as my body could take. Yeah, I'd cut down and lose weight, but I don't even want to think about how much muscle I was destroying.
I used to run first thing in the morning (for boxing) often 5-10 miles. Then I'd do a stepper or a treadmill later in the evening, for anywhere from 40 to 60 minutes.
I slowed that down over the years, but I was still doing too much and not realizing it. I'd heard bodybuilders in my gym, and from friends that I shouldn't be doing as much and that 16-25 minutes was plenty.
I'd like to say that I finally slowed it down after reading a lot of the experts on here, and what they had to say.
I now I walk for about 1 every weekday (lunch break at work), and I do about 20 minutes on a stepper or on a treadmill a few times a week.
That's been plenty, and remarkably, I'm actually looking better than when I was working my @ss off all the time!