I’ve gotta say that I’ve got a very prominent 6-pack, my secret? kayaking, and a lot of hard work
in the summer, I kayak for about 2 hrs a day.
and I also got one of those things where you clamp your feet on, and do upside-down sit-ups. a lot harder, but the results are worth it. you might wanna try one of those if you’ve got no back problems at all.
pretty much anything that includes a side-to-side motion gives stomach results. such as, kayaking and situps, to even splitting wood.
anyhow, just hard work is the way to go.