健身球

zhí lì zuò zài jiàn shēn qiú shang shuāng jiǎo píng fàng zài dì bǎn shang

直立坐在健身球上，双脚平放在地板上。

Sit upright on the exercise ball with your feet flat on the floor.

zuò zhè ge duàn liàn nǐ xū yào jiè zhù yī gè zhōng děng dà xiǎo de jiàn shēn qiú

做这个锻炼，你需要借助一个中等大小的健身球。

For this exercise, you'll need a medium-sized ball.