Plank locked, tap each shoulder, no hip sway.
Refuse to let your hips rock side to side, the stillness is the point.
Every tap removes one of your four contact points, so your core has to stop your whole body tipping toward the unsupported side, turning a static plank into an anti-rotation drill. The slower and stiller you move, the harder your trunk works. It is one of the best low-skill introductions to rotational core control, with nothing but floor required.
Lifting a hand halves your support for a moment, and your core has to cancel the twist that follows. The tap itself is trivial, the not-rotating is the exercise.
A wider stance broadens your base of support, so there is less tipping to resist. Start wide, then walk your feet closer together over time to keep progressing.
Slow and deliberate. Racing through taps lets momentum hide the rocking, while a slow lift, tap and replace keeps your obliques honest for the whole set.
