Muscle testing can be used to help you confirm your guidance when directly communicating with your Higher-Self. It can also be used to help you determine what is true, what is right for you and support you in making decisions.
Muscle testing works by choosing a body trigger that allows you to register a "Yes" or a "No." My favorite is self-muscle testing shown in the photo above, where you interlock your fingers. You pose a question in your inner-space and then try to pull them apart. If they hold strong, it's a "Yes!" If they easily can be pulled apart it's a "No."
With practice, this can allow you to let the communication of your Higher-Self bypass the mental chatter and become a physical body like experience. I've known friends that have manifested tons of success, beautiful mansions and traveled the World just from simply using this technique and trusting it.