Here is Christopher Reeves transforming nto Superman:
It's a lovely example of 'non doing' - in order to become superman you can see him allowing the pulls in his body that are taking his head off balance to loosen. This allows him to grow into his full stature. In his indecision about whether to reveal himself to Lois Lane you can see that he becomes a bit tense and 'does' tall, but then he settles back into his stature, and when he speaks as Superman you can hear that his voice is deeper and richer. Christopher Reeves, along with many actors studied the Alexander Technique.