Wmlbrown is correct. It would be 'bear down'. In this case, it means to tense your muscles and push downwards, as if you are trying to defecate.

Bare down, in this context, is probably a technical way of saying bend over

Possibly “bear down” which means to push down, lean and push down, exert your muscles or in some cases (not this one) move toward something rapidly and purposefully (as in sailing or boating). Could it have been “bend down?” That seems more likely in an anal exam.