Propulsion from both poles at once, with no leg kick. It needs no kick zone and, up to roughly an 8–10% grade, is often at least as fast as the diagonal stride.
Double poling keeps you moving even when your kick wax gives up — it needs no kick zone at all. That's why long-distance specialists train up to 50% of their volume with it. The typical mistake is treating it as an arm exercise: pull with the arms only and two kilometres later your arms are burning and you still have no speed. The impulse comes from the core — you hinge forward at the hips and drop your body weight onto the poles. Plant the poles level with your binding, not far out in front of you. What often gets missed: past roughly an 8–10% grade the evidence only covers parity — beyond that most skiers go back to the diagonal stride. And the technique lives on core strength — without it you mostly load your shoulders and back.