How does progressive muscular relaxation work in reducing anxiety?

By teaching the client to let go of muscle tension

In progressive muscular relaxation, the client is taught to contract individual muscle groups in order to give the awareness of tenseness or muscular tension. After the client has learnt to tense the muscle group such as the forearm, the client is asked to let go the tension. The client is told that the tension is what the client has at present and that s/he has to get into the opposite state. With repeated practice the client learns to relax all
the muscles of the body.