When a speaker alternately tenses and relaxes their muscles before speaking, this reflects a strategy of coping with nervousness that your text refers to as?

The answer to the given question is a coping strategy known as channeling your nervous energy.

Though you can choose to channel your nervous energy by keeping it to yourself, you can also exert it to your public speaking performance. Some ways of doing this include through creating interaction with your audience, speaking in a louder voice, and moving across the stage.