Cold exposure

Cold exposure works like weight lifting, you get stronger over time. There are little muscles around your veins that contract when they get into contact with the cold. After some time (only 1-2 weeks according to Wim) these become stronger, making your veins healthier and reducing the force that your heart has to use to pump blood around your body… Notice how you feel amazing after a cold shower and sluggish after a warm one. — http://www.icemanwimhof.com/wim-hof-exercises