Push-up position, hands wider than shoulders, straight body line. Brace core, neutral spine, shift weight to one side. Lower body shifting weight to one arm, extend other arm straight. Press back to center, alternate sides each rep.
Work one side at a time for max tension. Lean heavily into working arm, no straight up/down. Arms twice shoulder width, both straight at start. Keep body aligned head to feet, straighten hips over time. Film yourself or use mirror to check form. Feet together throughout.