Day 10 has no levels and no set count. One exercise, arranged as a ladder: 2 up and down planks, 30 seconds of rest, then 4, rest, 6, rest, 4, rest, 2. Eighteen reps in total, and that is the whole session.
An up and down plank begins in the high plank on your hands, lowers to the elbows one arm at a time, then presses back up the same way. The arms feel it, but this is a core exercise: with only three points of contact during each transition, the hips want to rotate, and refusing to let them is the entire job. The ladder gives you a small opening rung, builds to six in the middle while your form is still fresh, then descends so fatigue never meets the biggest number. Thirty seconds is short rest for a movement this taxing, which is exactly why eighteen reps is enough.
Hands under the shoulders, feet slightly apart, body in one line from head to heels. Lead with one arm for a full rung and the other on the next so both shoulders share the load. Watch the hips - rocking side to side means the rung is going too fast or the stance is too narrow. Finish every rep in a complete plank at both ends rather than half-standing your way out of it.
One exercise, five rungs, and a session that takes far longer to recover from than to perform.
Make it Harder: Do the middle rung with your feet together and keep everything else as written.
Make it Easier: Take the up and down planks from your knees and keep all five rungs.
