Day 16 keeps climbers in the anchor slot and slides a new plank variation into the second interval. Fifteen seconds each of climbers, plank rotations, climbers and a plank hold, at three, four or five sets with a minute of rest between them.
Plank rotations are the first time the program asks your core to work sideways while you are face down. From a high plank, the illustration shows the body rotating open into a side plank with one arm reaching straight up toward the ceiling, then returning to centre and rotating the other way. That opening movement recruits the obliques and the muscles that stabilise the shoulder, and it exposes any weakness in your trunk immediately - a rotation you cannot control is a rotation that collapses at the hips. Closing the session with a straight plank hold after all that movement is the program's way of checking whether the position survived.
Rotate from your ribs and keep your hips stacked so your body forms a single flat plane at the top of each turn. Press the floor away with your supporting hand rather than sinking into the shoulder. In the plank hold, hips level with the shoulders, glutes on, ribs down, breathing normally throughout.
Face down, face sideways, face down again - the plank position turns out to have more than one door.
Make it Harder: Hold each side plank position for two full seconds at the top of every rotation before returning to centre.
Make it Easier: Rotate from your knees rather than your toes and keep the reaching arm at hip height instead of overhead.
