stability ball        
noun [ C ] uk/stəˈbɪl.ə.ti ˌbɔːl/ us/stəˈbɪl.ə.t̬i ˌbɑːl/ (also balance ball, exercise ball, fitness ball, Swiss ball, yoga ball)
 (可以坐在上面或躺在上面进行体育锻炼的)抗力球,稳定球
a large ball for sitting or lying on while exercising
  There are lots of core exercises that can be done with a stability ball.  有很多核心的练习可以用抗力球来做。 
 Step 1: Lie face down on a stability ball with hips and thighs supported by the ball. 第一步:面朝下躺在稳定球上,用球支撑臀部和大腿。 
 - More examples
 - As far as workout equipment goes, stability balls and resistance bands are two of my all-time favorites.
 - Between lifts, she does crunches - and works a stability ball for balance and core strength.
 - You should only perform the plank on the stability ball if you have mastered the technique of the floor plank.