When speakers are tense and relax their muscles while waiting for their turn to speak, without calling attention to what they are doing, this reflects a strategy of coping with nervousness your text refers to as

channeling your nervous energy

Explanation:

In public speaking people get nervous because of the act of speaking in front of an audience. The main reason for people getting nervous is the reaction of the audience when they speak.

Speakers generally have a routine which distracts them from their thoughts and prepares them mentally for the task at hand. This routine is personalized for people but relaxing one's muscles is a common routine to channel one's nervous energy.

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