feedback on aikido pics

As you all know I'm new to SLR photography. I went to my bro's aikido test on Saturday and took these (and about 200 others). I was proud of myself that I used the Tv setting on my camera -from what I can tell I was at 1/200 shutter speed and varied between 4.0 and 5.6 on the aperture. I used the kit lens and didn't do any post-processing. The shots were obviously taken in a gym/warehouse setting with limitations as to where I could set up. I'm pleased with the "stop action" on most of them but I'm looking for other constructive criticism that will improve my indoor action shots. Clearly the composition could be changed with some cropping but as far as picture quality goes what can I do to improve? To me the shadows are distracting but I'm not sure that I can change that.

Dark. Think more of composition. Yes you can do that in post but if you do it before hand it creates less work and will give your shot more detail. Use the rule of thirds. Also if you were closer and had better composition, using a flash would brighten the photo up.

This is your shot

The photos look pretty good. They are a bit dark, which can be attributed to your slow lens. If you are going to continue shooting this look into getting a faster lens. If you had enough reach with the kit lens you may want to look into the 50 f1.8. That way you can get your aperature down more to expose the pictures better. It's a $70 lens and everyone should have one in their bag. I use mine a good bit for indoor portraits with available light. The depth of field is really shallow at 1.8, but you could get away with 2.8 and still get a good looking shot. You could also invest in a shoe mount flash like the 420EX or 550EX. I have the 550 and it will light up a room better than I though it would. Bounce it off the ceiling and you won't get those rough shadows and that "deer in headlights" look.
Otherwise in the shots, they all seem to have a guy standing over to the side, which to me is distracting. Something I learned reading a graphic design book is an object that stands on it's own away from the group will draw attention. Try to cut out the guy as AP did with his crop.
Otherwise, I think they look extremely painful. I hope I never find my body in that position unless I'm on a wakeboard. I hope the floor is padded.
Tiff

You didn't mention your ISO setting but I see you shot those at ISO1600. Good job! that's what it's there for. I figured you must have cranked it up to get f4+ at that shutter speed in that lighting.

I can still see a little noise even though you resized them down quite a bit. If you're going to shoot a lot at high ISO it's worth buying Noise Ninja to clean up your full size shots before you resize them down. A faster lens would help too as at that shutter speed you're barely freezing the motion (in fact you can just start to see a little motion blur around some of the fighters-actually more blur would probably add to the drama of those shots)

Watch your horizons also. Verticles like the sword racks should be verticle and the floor and roof line should be horizontal.