Your muscles are fatigued and filled with lactic acid. If the ice bath is not your thing, relax and soak ~45 mins in hot bath using 1 bag of Epsom salt and 1 large laundry-sized box of baking soda (aluminum free).
The Magnesium in Epsom salt relaxes the muscles allowing for more efficient healing. It also helps open the pores of the skin to absorb the baking soda. Baking soda (Sodium Bicarbonate) helps to alkalinize an acidic body after a long run.
Reference: Dr. James Fambro