Thera-Band Stability Trainer is used in exercise programs to improve motor skills and balance, particularly among the elderly, and for knee, back and ankle rehab. Two foam pads of different densities allow users to work through five progressive levels by starting on a firm surface and then either pad or stacking them. The green Stability Trainer is firm and provides a beginning level of challenge. The blue Stability Trainer is soft and introduces an increased level of challenge to the user. Easy to follow instruction manual included.