I wish my abs were concave vs convex. I maintain relatively high core strength for canoe paddling and heavy lifting/portaging, so my stomach bulges. I had to get a shot in my stomach fat the other day and the nurse had a heck of a time getting enough fat together for the injection. I attribute it to my sitting crunches. I use a cable multi-station weight machine and I use 80 to 90 lbs for the crunches.
I used to do 3 sets of 12 twice a week. Now I do them once a week as I have no long Canadian canoe trips planned for the foreseeable future.
Al