Supine leg extensions using a partner has been one of the most effective resistive stretching exercises. To apply proper resistance, the partner holds the ankle firmly and pushes down, applying an equal and opposite force to the resisting stretcher. However, the partner has to vary this force based on the resistance applied by the stretcher, and alignment may be a problem.
The non-moving resistance of the SG’s crossbar offers ideal resistance and alignment without requiring a partner!