How to pronounce “ischium” in English

There are many who use balance balls But balance balls are unstable right?When you are supposed to sit down with your ischium and both hands aligned When you get on the balance ball, it becomes more unstable, and contributes to the trainIt would contribute more to the strain With the unstableness of the balance ball To eliminate the unstableness, it uses your core, often called the core training, and it helps to strengthen the core