Hmm... I had no idea that Adolph Hitler could convince an entire country's populace to elect him and support him in getting rid of Jews and trying to conquer the world merely through his muscle contraction and planetary gravity. And all this time I thought it was the power of his oratorial skills and his skill at propaganda... see - you learn something new every day!
Benjamin is talking about literal
power, as were you up until this post. This post, instead, is all about skills
(your word, not mine), which you are figuratively
approximating with power in a way that is completely irrelevant to the subject of this discussion.
Benjamin's assertion is that the only powers -- that is, scientifically speaking, energy sources for performing work -- to which the human body has access in and of itself are muscle power and gravity. Your sarcastic comment about Hitler's oratory not only fails to disprove this assertion, but fails to address it at all.