Here's my current lament. Intense cardio for long periods of time,- ie marathon training- eats muscle. Your heart rate surpasses that fat burning zone and starts eating the carbs and protein, not the fat. So whenever I hit this stage in training, all the hard work I put into my triceps and thighs - totally gone.
So as soon as my training is over (two and a half weeks!) it's back to the weight room to tone up. Just declaring my intention so you can hold me accountable.
But glean the bit of information from the top, it's hard to tone up and build muscle if you do regular high intensity (2 hours) cardio a few times a week. By high intensity, I mean your heart rate stays at darn near max the whole time.