Technically you stretch a tendon every time you move.

How would you stretch just a muscle as opposed to either stretching just a tendon or a tendon and a muscle together?

Are you saying that you should avoid over stretching? I'm not too clear on where you're coming from.

I think you're confusing tendons with ligaments.

Ligaments join bone to bone, their job is to stabilize joints. Tendons connect muscle to bone and if they could contract and stretch then you wouldn't be able to move.