One of the toughest vaults is the Amanar, named after 1996 vault champion Simona Amanar. It consists of a roundoff onto the takeoff board, back handspring onto the table and 2.5 twisting somersaults before landing.

Most countries are lucky to have one or two gymnasts who even try it, let alone do it well. But four of the five Americans — Aly Raisman, Jordyn Wieber, Gabby Douglas and world vault champion McKayla Maroney — land the high-scoring skill.

It's got a start value — the measure of difficulty — of 6.5, a whopping 0.7 above the vault most other gymnasts do, and on Tuesday the Americans ripped off one massive one after another. It gave them a 1.7-point lead, and they never looked back.

— Nancy Armour — Twitter www.twitter.com/nrarmour

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