I only had time to do an 18 min HIIT if I wanted to have time for an ab workout. I did vacuums (I think that's what they're called) and side bends with weights. I also did bicycles for 60 seconds and a 30 second plank. However the workout I started out with was the ab bench where you do a full crunch through moving both your head and legs up... I am now up to 20 pounds for 6 reps. I'm pretty pumped, since at first I couldn't even do 12 reps with 0 weight!!