If you've been out on a running trail recently you might have noticed one or the other person wearing what appear to be fancy-looking post-op socks. They apply graduated compression and are tighter at the bottom and gradually looser as they go up the leg.  Similar to muscles they compress the veins and help return the blood to heart and lungs. After my last trek form Zurich to Basel I was rather surprised to see what the first 6 hours did to my calf's blood vessels. One or the other reminded me more of a hire hose than anything human; not exactly what I need on my daily 12 hour hikes. Therefore my decision to go for compressions tights. The reason why I didn't choose an integral sock, e.g. Rohner's compression outdoor, is that I want to be free to take the tights off if the temperature gets too high.