And compartment bleeds - they are totally cool phenomena so long as you aren't the one experiencing it! Muscles are wrapped in fascia that helps the different muscle bundles slide along against each other. This wrapping means that if a vessel is injured inside the muscle bundle, the bleeding can be trapped within the muscle, causing damage.

In my case, I received a direct kick square in the middle of my right thigh, directly over the rectus muscle. The muscle swelled because of this kick, and an artery was crushed and bled into the muscle. Keep in mind that arteries are high pressure systems, veins low pressure systems. The pressure from the swelling muscle and the pooling blood effectively created a tourniquet that cut off my veins' ability to carry blood out of the muscle. Intact arteries, being high pressure, were able to keep bringing blood into the muscle though, so more and more blood just kept coming into the rectus. It just kept swelling and and swelling within the fascia. Remember also that I was on coumadin when I was kicked, so that I bled more easily than the average person would have. Eventually, the swelling crushed the muscle in the fascia, and that section of muscle died. It had to be removed surgically (along with a grapefruit-sized blood clot that formed within the rectus).

Hope that answers your question.