Yes, it does!
To measure the effects of power posing, half the group was asked to stand in a high power position and the other half was asked to stand in a low power position (think slouched/guarded posture). After two minutes, testosterone and cortisol levels were measured and then compared to pre-pose levels.
The results?
The high power posers experienced a 20% increase in testosterone (dominance) and a 25% decrease in cortisol (stress). The low power posers experienced a 10% decrease in testosterone (dominance) and a 15% increase in cortisol (stress).