The 4-inch tall BOSU® PowerStax™ are designed to add additional height to the 65cm BOSU® Balance Trainers, depending on how many PowerStax™ you stack together. This feature can not only physically elevate your experience, it can improve the versatility and intensity of your workout. The PowerStax™ stabilize the balance trainer dome up or dome down. Whether it’s a step-up or box jump you require, the PowerStax™ rise to the occasion. The PowerStax™ alone can be filled with water and used for additional top-down stability exercises.