弯曲两膝。

Bend both knees.

youdao

人体卧于瑞士健身球上，两膝弯曲，足平放于地面。

Lie on a Swiss ball with your knees bent and feet flat on the floor.

youdao

双膝弯曲，两脚着地，躺在这个滚筒上，让它沿着你的脊柱，一直从尾骨到头顶。

Lie on the roller with your knees bent and your feet on the floor, so the roller extends along your spine from your sitting bones to the top of your head.

youdao