This strategy is from the Center for Clinical Interventions (CCI) by the Department of Health, WA.

When you feel stressed or anxious, your body has this quirky way of reacting – it tenses up your muscles, getting ready for action like it's a superhero going on a mission! But here's the catch: sometimes it goes into superhero mode even when there's no real danger around. You might not even notice it happening, but your muscles can become super tight. Maybe you've caught yourself clenching your teeth, making your jaw feel all stiff, or noticed that your shoulders are constantly up by your ears. One method of reducing muscle tension that people have found helpful is through a technique called Progressive Muscle Relaxation (PMR).