It is also possible to use individual cuffs - for example, a single leg cuff or only one arm cuff. For this you need the blind plug. This is a small piece of plastic that is stuck in the back of your Quick Connector.
When you pull this blind plug out, you can use it to close the port for additional cuffs on the Quick Connector. This allows you to easily connect a single cuff without leaving a port open and allowing air to escape.