Well, my personal experience my be anecdotal, but when I increased my running mileagel to train for my marathon, I turned into a mushy flabby mess.
After my marathon, within in a very short period of time (like two or three weeks) after resuming my strength work, I got smaller and toned.
Concentrating on aerobics doesn't work for me. I have tried and tried because I do so love to run. It's so much easier than getting out all that equipment.
And, articles like this with the message "increasing muscle mass is so difficult and really doesn't help you lose weight, although you SHOULD be adding strength training to get a well-balanced fitness routine" do nothing but discourage "uneducated" women from lifting heavy weights which drive me crazy. (Whew! That was a long sentence!)
I see it in my friends who are approaching 40. They're turning softer as they age, even the ones who go to the gym. My DH always comments about this. He says "They LOOK like they're almost 40, but you don't." Ah, gotta love him.