Wow, this's a good discussion. I'm diggin' it. I have found that at 19 years of age, 160 LBS, and lifting... that if I cycle and do lots of cardio... that my metabolism is SO HIGH that it *does* take away my muscle. I have to actually sit on my ass to keep my muscle.. believe it or not. I eat 6-8 meals a day, making about 2750-3000 calories a day. My GOAL is to bulk up, and get a bigger chest and arms. I've found that since I stopped cycling so heavily from summer, I have easily put on the muscle. In the summer when I'm biking like crazy, I drop down to 140-145 LBS in no-time flat, I lose all my muscle (cept legs ), and get REALLY skinny.

To balance this out, I began supplementing. I take whey-protein shakes 3 times a day, as well as try to eat "clean". (NO fast food, NO pop, lots of veggies, peanut butter, fruits, nuts, salads, fish, chicken, potatoes, etc). I've put on a little bit of fat since my weight-training has started, but just as quick as I gain it, my muscle burns it right back off. I must say that with my weight-lifting since August of this year, I have put on 20 lbs of muscle, look & feel better, and can EXPLODE on my bike. I can "sprint" on my bike a helluva lot faster and harder than I used to, even just this year.

As a whole it's a "balance" and it certainly depends on your goals, or what you want. For me, I have to watch my amount of cardio. For heavier set people, the more cardio the better. Genetics, BMI, and body-type have a LOT to do with it too.

Hope that helps some-what.

-Matt