It doesn't mean anyone has to be less powerful. It's all in the pose. Social scientists have long noticed that we humans tend to complement another person's pose. If the other person is dominating, we retreat or at least dial it down a bit. However, if you want to take the power, or at least not lose your advantage, it's a better strategy to mirror the other's pose. If they lean forward, you lean forward. If they sit back, you do the same.
It's a given that the video in our lives trumps the audio - that how we behave is bigger than whatever words we choose to say. Our nonverbals govern how others think and feel about us - but the newer thing is that researchers are discovering that our nonverbals also influence the most important person in your life - YOU! Your presence, your thoughts and feelings, impact how you carry yourself, and the tape you play in your head. That's what this 5-minute clip below is all about - it contends that tiny tweaks in your posture going into a stressful event can lead to big changes, one that encourages acting powerful and dominant, which are two pretty awesome adjectives to bring with you to a job interview, or anywhere else you are lookin' to score a win.