Jump wide, drop into a squat, reach across and tap.
Land soft and keep your chest up, drive the cross-body reach from your obliques.
The stance jack fuses a jumping jack with a squat and a cross-body reach, so your core is decelerating a landing, holding a squat, and rotating within a single beat. The obliques drive the reach toward the opposite foot while the trunk resists collapsing forward in the wide squat. As a timed move it doubles as conditioning, which is why it lives in circuits where you want core work that also keeps the heart rate up.
Mostly through your trunk, especially the obliques driving the cross-body reach, with your legs working the jump and squat. If you only feel your legs, slow down and make the reach a deliberate twist rather than a token tap.
Step your feet out wide instead of jumping, keeping the squat and cross-body reach the same. You keep the rotation and core work, and lose the landing forces.
Twenty to forty seconds of clean reps beats a minute of collapsing form. Keep chest up and landings soft, and stop the interval when the reach starts turning into a forward slump.
