Complete 8 rounds of 20 seconds "work" followed by 10 seconds rest of:
Post total number of reps for each exercise to comments.
Since leaving the old "Fitness Zone" building back in Aug of '10, the only thing we have really missed was the GHD machines. Most of us used them to do hyperextension situps (or GHD situps). MAN, those hit your abs hard! I remember being sore from GHD situps for 6 days once.
GHD situps were problematic though. Only a few could do them safely. Most folks experienced fairly significant back pain when doing these movements due to the fact that the spine is virtually unsupported during this exercise. Again, fine for some. Not for most.
We now have a better version of this movement. Enter - Anchored Stability Ball Situps. This movement yields nearly all of the same benefits (more really) of the GHD situp, with fewer drawbacks (back pain).
To do this right, place the ball in a comfortable position where your back will be supported throughout the movement. Anchor your feet to an immovable object. Complete a full ROM situp by hyper-extending the trunk backwards (stay supported, now). Returning back to the full upright position. Legs should stay nearly straight and locked at the knees throughout the exercise.
If you need core strength, consider working your way up to several sets of 10-20 reps per day. But BE CAREFUL! These can make you "Stupid Sore" if you overdo it.