Professional Aquatic & Underwater Workout This high-tech option upgrade of PRO SWIM SPAS series adds the option of underwater treadmill to Athena and Apollo, greatly improves the sense of technology of these two PRO Swim Spas, and actually increases the interest and function of sports for these two PRO Swim Spas. The underwater treadmill is driven by hydraulic pressure, water and electricity are separated with very safety factor. Running speed can be adjusted by the control panel from one to nine levels, from one kilometre per hour to eight kilometres per hour, suitable for users with different needs.