Day 16 is standing work with the counts doubled on the legs: 6 torso twists, 12 side leg raises and 12 back leg raises, straight through before you rest. Back leg raises are new - standing tall and sweeping one straight leg behind you, then the other, with the torso staying upright rather than tipping forward to make room.
The three exercises take the trunk in three different directions from the same spot. Torso twists rotate it. Side leg raises make it resist leaning sideways. Back leg raises make it resist arching, which is the hardest of the three to notice and the most useful to train - the natural cheat is to lean the chest forward as the leg goes back, and refusing to do that is exactly what turns a leg exercise into a core one. Add the balance demand of standing on one leg for twenty-four of the session's thirty reps and you have a quiet session that asks a lot of the deep trunk muscles.
Keep the hips square and facing forward on the back leg raise; the leg does not need to travel far, it needs to travel without taking your spine with it. Squeeze the glute at the top of every rep. On side leg raises, stand tall and let the standing leg do its stabilising job. In torso twists, turn from the waist up and let the head follow the shoulders rather than leading them.
Three directions out of one standing position, with your trunk holding the whole arrangement together.
Make it Harder: Take the back leg raises at a three-count out and a three-count back with the hips locked square.
Make it Easier: Halve the back leg raises to 6 and keep the other two exercises exactly as written.
