One interesting data point is a survey carried out within the Society for Creative Anachronism.
If you're familiar with armored combat within the Society, skip this paragraph. The Society, or SCA uses weapons made of rattan and other materials that approximate the weight and balance of medieval weapons. The goal in armored combat is to strike a "good blow", one assumed to hit hard enough to be effective against medieval armor of a particular period. Lighter blows than this standard are ignored.
This article describes a survey carried out some years back to attempt an objective quantification of this subjective standard by smacking a bowling ball off a post and measuring how far it flew before hitting the ground. It should be possible to calculate the number of Joules transmitted to the target. Unfortunately, the calculations are trickier than I originally thought, and for now I will simply direct you to the first comment below, which responded to an earlier draft. These estimates seem to assume a single handed sword, and a significant number of people can hit harder than the upper end of the range if they want to: the Society frowns upon hitting harder than necessary for safety reasons.
It's also important to remember that many blows in combat land with less than the optimal amount of force the striker could deliver, typically because the target moves in a way that makes the biomechanics less than ideal.