Hydraulic system provides zero starting resistance. 6 Levels of resistance. Dual resistance to work opposing muscles with positive resistance exercise. Low impact on joints. Save exercise in unsupervised conditions. Ideal for rehabilitation and strength training.Hydraulic system provides zero starting resistance. 6 Levels of resistance. Dual resistance to work opposing muscles with positive resistance exercise. Low impact on joints. Save exercise in unsupervised conditions. Ideal for rehabilitation and strength training.