The 10-minute workout: Pick 4 exercises and do 3 sets of each: 20 seconds on/ 20 seconds off. Then do 3 sets of back extensions. Make sure you include each muscle set ( Lower Abdomnials, Obliques, and Upper Abdominals) at least once.
Go slow and steady
Stuck in your gut. (tighten up the muscles like you are trying to pull your belly button in)
Watch your back you are working your core not your back if you are feeling your back too much you are doing it wrong.
Beasts (Lower Abdominals)
Lie on your back, lift legs slowly up in then back down, then lift hips up and back down.
Leg Circles (LA and Obliques)
Lie on your back lift legs slightly and circle legs around
Twisting Toe Touch (Upper Abdominals and OB)
On back with legs straight up, twist and touch opposite toe with opposite hand
On back start with arms at your sides and slide them down to your knees
Bent leg sit-up (note do not need to touch your elbow to your knees- going all the way up does not add that much to the exercise)
Reverse Crunch (UA and LA)
On back bring bent knees up to your chest
Crunch with a twist (UA and OB)
Crunches alternating straight up, left, straight up, right
Alternate leg lift (LA and UA)
Legs slightly off the floor lift one then the other
Leg overs (OB)
On the floor bring both legs to the left, center then right
Lie on your stomach, raise both arms and both legs up can also be done alternating opposite one arm and one leg.