Day 16 brings the elbows down to the floor. Three 20-second stations - elbow strike sit-ups, sitting elbow strikes, flutter kicks - at 3, 4 or 5 rounds. Notice the quiet progression: the ab intervals have grown from 15 seconds to 20, a third more time under tension at every station.
The elbow strike sit-up marries Day 9's close-range weapon to trunk flexion: rise through a full sit-up and throw a horizontal elbow across the body at the top, alternating sides, so every rep ends in rotation. The sitting version then strips out the up-and-down and keeps only the hard parts - the lean-back hold and the turning strike - which makes it an isometric for the abs and a rotation drill for the obliques at the same time. Flutter kicks close the round with the lower abs, as they have on every core day so far.
Come all the way up before the elbow fires, and make it a strike - short, sharp, body turning behind it - rather than a vague wave. In the sitting elbow strikes, find a lean-back angle you can hold for the full 20 seconds with a long spine, and rotate through the ribs, not just the arms. Flutter kicks stay low, fast and continuous, lower back welded to the floor.
Twenty-second stations and elbows in the sit-ups - the core days are growing up alongside you.
Make it Harder: Sit an inch lower in the lean-back during the sitting elbow strikes and stay there.
Make it Easier: Rise to crunch height instead of a full sit-up and keep the elbow strikes as written.
