Was it exercise, diet a combination or genetics?

I think it all depends on where your body carries fat. Some people carry it all in their hips and have flat abs, others carry it all above the waist or spread evenly all over.

If you get down to a fitness range of body fat, you could probably have flat abs without excercise.

I gotta get them before I can answer this question. I carry all of my weight in my mid-section/tummy. Even with the great weight loss I've had, I still have a small belly. I need to get to doing some exercises and try to flatten it out.

When I was younger and working out/lifting weights like crazy, I had a flat stomach without even doing any ab work. It was genetic for me back then.

But now, my stomach has lots of weight on it still. I'll try to lose as much as I can to get rid of it. And then start with some ab work/weight lifting again.

my stomach was flattest when I lifted heavy and ate clean.

Diet reduces the layer of fat around your midsection. And for *most* people, the "flat" abs only come when you also do exercises that work your core. That doesn't necessarily mean situps - I had the flattest stomach of my life back when I was cycling three times a week, and walking every morning - and I never did a specific "ab" exercise. This was after having a child. "Core" strength is important for a lot more than just a flat stomach too, a strong core can relieve/avoid back problems and hip alignment issues now and later in life.

IF you've had children, surgery, or any other major strain on your ab muscles, there's always a chance that the muscles tore or were damaged in a way that will never allow a completely flat stomach, I'm pretty sure that is the case with me from my youngest child's birth.

Me too. After 3 c-sections, I haven't a prayer of flat abs. I did however, FEEL sore muscles in that area after sledding and holding onto my littlest. Maybe there is a speck of hope for that area? Maybe?

I would say diet and ab exercises

Ditto what Scorbett said. Truly flat abs require core strength. Which comes from exercise for most of us. The older we get, the more we tend to lose our core strength if we don't exercise. Now, if you have core strength but are also overweight, you will still not have a "flat" stomach. So sure it is both diet and excercise. But I've seen many small, not at all overweight people with little core strength and a "pooching" belly.

IMO, In addition to straight "ab" exercises, squats are one of the best ways to flatten your abs...they are incredible for building your core.

Oh, I used to ADORE squats. That's what probably helped me with my abs back when I was weight lifting heavy.

LOL, can't say I adored the SQUATS, but I sure adored the RESULTS! I used to lift heavy, my workout partner for a few years was a professional waterskier. I can't wait to start lifting again! Soon, soon...weight loss first!

I love the feeling of being strong that the squats gave me (and love the way it made me look too ). Loved deadlifts too for the stretch. Leg work and shoulder work were my favs (hated ab work).

I'm waiting until I'm closer to goal before I start lifting again (or when I'm at goal). I'm sure I'm going to lower my goal by at least 10 pounds, but for now, I don't want to see that I have to lose 20 + more pounds again. All psychological.

I wonder if laying on the floor in a 'Plank' pose, watching TV would be considered a good core workout?

Yoga plank pose, yes! Laying "like a plank", not so much!