Sets: 3，Reps: 45 seconds
3组动作，每次坚持45秒
Begin in plank position with hands balancing on top of a medicine ball. Keep abs drawn into spine and think about pressing chest away from the ball with strong arms as you hold the position. (Place feet wider apart to make the move easier; add a challenge by moving them closer together.)
双手放在健身球上，支起身体。让腹肌紧贴脊椎，在坚持姿势的同时运用臂部力量努力让胸腔远离健身球。（让两脚分开的距离大些做起来会更容易；想要增加挑战的话，缩小双脚间的距离。）
