Foucault says somewhere, I think in one of his interviews though I'm not sure which one, that for there to be power relations at all there must in a very minimal way be a kind of "consent"/participation on both sides. Otherwise it's not power, but simply force. I think at the limit of this definition we could think of a prisoner whose limbs are completely immobilized by chains. As long as he is able to choose whether to talk back, spit, grimace, etc., this is a relation of power. But his ability to act is clearly so slight in this scenario that it could easily turn into a completely senseless beating. Just force.
Depending on what you mean by consent, I would either agree with the above or suggest that consent to oppression is impossible.