Butterfly forward movement is caused by arm pull and hip movement upwards.

蝶向前是靠拉臂上提臀促成。

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During, or at the end of the arm pull-down of the first stroke after the start and after each turn, a single downward butterfly kick is allowed, but not required, followed by a breaststroke kick.

出发后或每一次转身之后，在第一次大划手之当时或之后，一次向下蝶式踢腿是被允许的(非必要的)然后拌随一次蛙式踢腿。

youdao

During, or at the end of the arm pull-down of the first stroke after the start and after each turn, a single downward butterfly kick is allowed, but not required, followed by a breaststroke kick.

出发后或每一次转身之后，在第一次大划手之当时或之后，一次向下蝶式踢腿是被允许的(非必要的)然后拌随一次蛙式踢腿。

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