Plank on the dome, tap a shoulder, and resist the twist.
Keep your hips dead level, do not let them swing when a hand lifts.
Every time a hand leaves the dome, your base of support halves on a surface that was already moving, so your core has to kill the rotational pull that wants to swing your hips toward the lifted arm. The wide foot stance helps, but the anti-rotation work still lands squarely on your obliques and deep midsection. It earns a place as one of the best tests of whether your plank is genuinely braced or just posed.
With both hands on the dome the platform is barely stable, and lifting one hand puts all that instability through a single arm. Your core has to work double, resisting rotation and steadying the wobble at once.
Widen your feet, slow the taps right down and shift your weight subtly before lifting the hand. If they still swing, go back to flat-ground shoulder taps until they are silent.
Core. The tap is just a way to steal a support point, the training effect is your midsection refusing to twist while it happens.
