My style of karate is Uechi-ryu. It is considered a "hard" style (as opposed to a "soft" style). One of the biggest parts of our style is a test we perform for our first kata called Sanchin Testing. The kata is Sanchin, and the test involves removing your shirt, and standing in your Sanchin Stance while the tester strikes your abdoman, arms, legs, neck, etc. This is designed to demonstrate the ability to absorb the impact and maintain the proper stance and dynamic tension in your body. As you advance in rank, the testing typically involves harder and harder strikes.
To train for the ability to take this kind of pounding, we have activities that are designed to get us used to it. We do arm. leg, abdomen, etc. conditioning, which involves two people hitting each other in specific ways to toughen us up.

I used be great with this. I could take a pretty brutal pounding just about anywhere. I still can, but it hurts like hell now.
After loosing 30 pounds, my whole body dynamic has changed. I have less fat, which means less padding. This means more pain when conditioning. We did arm conditioning the other night, and the pain was bad! Getting punched in the abdomen, I am sliding backwards instead of sticking to the floor. Sparring is different also, since I have 30 fewer pounds to throw around.
I'm slowly getting more comfortable with the reduced weight, and I'm putting an effort into bulking up by lifting and doing P90X, but it has really surprised me how things have changed. Has anyone else seen this affect with weight loss and martial arts?