Then, kick your legs up and down together in a whipping motion generating from the hips and bending at the knees, as if you were a dolphin.

通过髋关节和膝关节用力运动，上下踢你的腿，就像海豚一样。

youdao

A whipping or lashing motion or stroke; a whiplash.

鞭打抽打，鞭打的动作或一抽、一挥；

youdao

The fact that, before this unusual motion was tabled, some of Mr Brown's Labour detractors were privately whipping up the controversy over the policy added to David Cameron's calculation he could do some real damage with this debate.

BBC: Brown comes out fighting