The Medela Spring Express uses a piston and the large muscle of the arm creating less stress than those manual pumps using the hand.  Insertion of the spring into the cylinder provides assistance in the piston release to complete the suck, relax, release cycle similar to a baby's sucking pattern.

Instructions: For expressing milk from the left breast, hold the flange section with the left hand.  With the right, push the piston in fully allowing the spring to assist in returning the piston to its original position.  Reverse for expressing milk from the right breast.  By using the arm opposite of the breast being expressed, the large muscle of the arm is used creating an easy pump session.