Why? The science behind ice therapy is actually pretty interesting. It starts with the fact that following intense exercise, (for me that was 16 miles+ in the cooler months and 13 miles in the summer), your muscles experience microtrauma, or tears to muscle fiber. The cold water helps to reduce swelling and associated breakdown, constrict blood vessels which then flush out wastes like lactic acid, and decrease the metabolic process and physiological process that can encourage more immediate recovery. Of course, these baths provide several other preventative benefits often associated with ice packs on the knees and dehydration recovery.
The general rule is to sit in water that is 35 degrees cooler than your body temp. Often the cold water faucet will provide enough of a difference to give you these same results. This could also be a swimming pool or stream. The suggested time is 15 - 20 minutes and ideally you follow this soak with a warm shower about 45 minutes later. Again, more recovery pluses for going the way of a cold - hot combination.
Does it work? Let's just say that on many long run mornings, I have seriously struggled getting up the stairs and into the tub. I sit in the ice bath for 20 minutes, (a large glass of chocolate milk alongside), and once I get out I am literally dancing across the floor. I have experienced very little soreness throughout training and I owe it all to A & K B, and absolutely none of it to Mr. Van Winkle!