Abdominals can and should be trained multiple times throughout the week, unlike other muscles that need extra days of recovery. Three sets of 10 for each exercise is a good starting point.
Upper abs:
Decline sit-ups:
3 sets of 10 reps
A great start is the decline-sit up, which forces you to work against gravity.
Midsection:
Jackknife sit-ups:
3 sets of 10 reps
These jackknife sit-ups are great for working the middle section of your abdominals, as well as your quads and hamstrings. They’re more challenging and dynamic compared to the standard crunch.
Lower Abs:
Leglifts:
3 sets of 10 reps
The leg lift motion is crucial for attaining the V-shape that your wife desired you to have for years. They work the lower abdominals and the quadriceps, and can be done hanging from the pull-up bar as seen in the above example. That version is more challenging than doing them with your arms resting on the dip machine. Either way is effective and necessary for any complete abdominal routine.
Obliques:
Twists/Wood-choppers:
3 sets of 10 reps - each direction
A common mistake for most gym goers and folks who don’t hit .400, is abandoning the obliques. A smart workout for developing these oft-untreated muscles are the wood-chopper exercises using the rack as seen above. Rotate your hips to either side with your arms extended, and you can feel the tug on the sides of your body, abdominals, and hip flexors. You can also do these holding a dumbbell out using both hands to grip.
Lower Back
Supermans:
Hold pose for as long as possible - 3-5 sets.
Depending on your preference, you can either work lower back on your back day or on your ab-days, but make sure you don’t forget either way. Supermans are a good finisher for a core workout and damn tough to boot. You’ll feel it in your lower back, big time.
