I don't know what it is specifically, but it's medical. I've seen them before and always assumed they were for some sort of elbow injury; sort of like a knee brace.

It's the usual treatment for "Tennis Elbow"

That was actually my first thought also, as I have an elastic arm band that is somewhat similar. I was under the impression that its function is simply to dampen vibrations that would otherwise reach the elbow while playing tennis, so I don't understand the purpose of wearing it full time.

Jim

Having a bit of a wonky left elbow myself let guess a little based on my experience. When I hold my arm in the crooked (90 degree) position with any amount of weight the tendons fatigue quickly. When I wish to straighten my arm I have to first drop my shoulder to change the angle and stresses. Then the arm will straighten without the risk of dropping the object. In my case the tendons and nerves are out of position a little; probably the result of some choke escape drills in karate. My orthopedic surgeon said he could fix it in about 15 minutes, and $4,000. All that to say this: the black band most likely keeps pressure in the tendons so he doesn't have to do the fandangle that I go through.

Final note: The black band probably has nothing to do with living off the grid.