Day 16 spends most of the set with the legs off the ground and finishes face down. The circuit is 10 flutter kicks, 10 leg circles, 10 scissors, 10 back extensions and a 10-count hold, in order, 2 minutes rest, 3, 4 or 5 sets. It is close to Day 8's shape - three raised-leg exercises then back work - but the hold is different, and that difference matters.
Flutter kicks, leg circles and scissors are three ways to load the lower abs from the same lifted-leg position: alternating up and down, circling, crossing side to side. Doing all three in a row means the legs stay off the floor for 30 reps, and the abs get no reset. Then you turn over for 10 back extensions, and the hold that follows is not a stretch this time: it is the back extension held at the top - chest lifted, hands at the temples - for a 10-count. That turns the back work from 10 reps into 10 reps plus a static hold, and it balances the long stretch of lower-ab time that opened the set.
Flutter kicks are 5 per leg, scissors 5 crosses each way, leg circles 5 each direction. Keep the lower back pressed down through all three, and set the legs down between exercises only if the back starts to lift. In the prone hold, the lift is modest - a few inches of chest off the floor - and it should be felt along the length of the lower back, not pinched into one point. Keep the feet down and breathe.
Thirty reps with the legs in the air, then ten counts holding the chest up - both sides of the trunk hold their line.
Make it Harder: Lift the head and shoulders off the floor for the flutter kicks and scissors.
Make it Easier: Set the legs down for a moment between flutter kicks, leg circles and scissors.
