Question Regarding Muscle Building Exercises

I take the same stance on body weight exercises and ab works as the rest of my body. Muscles grow in rest, and the abs are a muscle group, so I give them a day rest between sessions. Core strength is extreamly important for your lifts. To build strength in your abs do the exercises with weight. I do my decline bench sit ups with a plate weight, always have. I got scolded by a personal trainer because it will make my abs big and bulky, lol, and women don't want that. Heck, if they are bigger maybe they will show at a lower bf percentage and if they are big they will look insane once you can see them.

Recovery is more about sleep, hydration and proper nutrition... seeing your abs happens to about pretty much the same things.

It bothers me that people fear over-training when exercising only 3 days per week. You'd have to be doing 3-a-days on your training days for that to be a possibility. Someone getting 7+ hrs of sleep every night, drinking at least 12 cups of water a day, and taking in 1 gram of protein per pound of target body weight will recover quite nicely and be perfectly capable of training 5-6 days a week, no problem.

I love bodyweight exercises for many reasons, especially the simplicity and lack of necessity of a gym to do them. I suggest doing bodyweight work like pushups, planks, side bridges, pullups, etc. on most days. I hate situps and will not have any of my clients do them - they put a lot of pressure on your spinal column, which is meant to stabilize us (prevent our bodies from collapsing) not scrunch us into a ball. Trust me, planks and bridges will tear your abs up just as much, if not more than situps and you don't risk spinal cord damage. If you want something with a rep count instead of a timer, go with leg lifts (keeps the spine in a neutral position).

I hope this helps and you see the gains you want.