I’m not sure it’s the sharpness of the sword so much as it’s tensile strength and the power with which it’s swung. A very dull blade could easily cut through many people if swung with enough force. You see this all the time with industrial accidents where one or more people are killed by a snapped steel cable or other piece of machinery (like farming equipment). A samurai will whip his entire body into a swing, probably generating close to a thousand pounds of force behind a very sharp blade. This should be sufficient to cut through at least two people and maybe more. If that is the power of an average samurai, someone beyond the 4th standard deviation (in terms of strength) might be able to pull off 4-5 people, probably depending on their arm length. Remember that a sword swing only carries sufficient power through a portion of it’s arc. Another factor would be the people being cut in two. Is it 4-5 people the size/build of a jockey or 4-5 people the size of Hulk Hogan? My guess is the former.
Welcome to the SDMB, basildave.
A link to the column you’re commenting on is appreciated. Providing one can be as simple as pasting the URL into your post, being sure to leave a blank space on either side of it. Like so: http://www.straightdope.com/columns/read/2810/could-historic-japanese-samurai-swords-cut-a-human-body-in-two-with-one-stroke
I’m not sure a samurai, in the heat of battle, would necessarily be taking baseball bat swings. If he misses, he leaves himself defenseless. I imagine most of the swinging force in battle would have been generated by the arms.
I’ve cut things (no, not people) with a sword before. You don’t do a huge swing like a batter, but you don’t just use your arms either, at least not if you want to cut through anything. You definitely have to get some torso and leg movement in there for proper cutting technique.