Aren’t kendo sticks split into a few parallel sections and then bound to hold them together? The further questions will deal with this; if they aren’t, we will just address it as a hypothetical sword.
My belief is that a sword like that would be spilt and then bound to reduce te shock on the weapon. As I remember, kendo is a pretty hard-hitting sport. However, I have also heard that by doing the splitting, it increases the damage inflicted. What is the straight dope?
I have one, and they’re made like you described them, with the parallel sections made into a hollow tube. This should, IMO, enable to sword to compress slightly when you hit something, which would take some of the energy out of the attack. I’ll think about it, but I can’t see any reason that the splitting would increase the shock.
Kendo sticks are split to reduce the shock of impact as ryoushi noted. They also are tension adjustable to vary the stiffness and thus, the force that can be generated with them however, they will not ever be as hard hitting as say, a bokken. You have to ask yourself, how can a modification done to decrease shock be used to increase damage? They are mutually exclusive properties.
It’s still better than the oak sticks they used before. I mean, really, unless they switch to Nerf, it’s not going to get much better than that. 
I can’t see a well-kept kendo stick doing much damage. Now, a broken, splintered one is entirely different. Yikes. Split bamboo HURTS.
Solid wood weapons (bokken) are still used – just not so much in Kendo. In addition to being less damaging, the split bamboo shinai allow for much faster wielding than bokken with much less physical strain. The shinai is for sport only. The bokken, on the other hand, can be an actual lethal weapon if wielded properly (or terribly improperly).
It can be argued that the user of shinai does himself a disservice as the weapon can be muscled about easily without attention to proper technique. The heavier bokken demands greater attention to form with each movement. Choppy movement and incomplete strokes will fatigue the wielder in short order. However, the speed, ferocity and repetition of Kendo will likely affect the same net result on form over time.
I am not an expert. I don’t even play one on television.
Back when I was training in martial arts, our teacher would sometimes bring out a shinai and smack us with it (not abusivly or anything), making sure we were focusing properly. One person in the class said that the split strips of wood will pince your skin when you’re hit if you weren’t tight enough - I’ll have to disagree with that one though. You could never flex so hard that your skin can’t be pinched, even if you had 0% body fat. We were never hit on bare skin though, so I’ll leave that for someone who has. I’ve been hit a lot with a shinai, mostly on the legs and stomach (albeit never from a real attack). While it stings and may leave some small bruises, you’d have to be hit extremely hard on those body parts to do any real damage. Hitting someone in the neck, head, or elsewhere with a shinai would be uglier.