If a careful warm-up helps prevent muscle soreness, what does the cool-off period do? Can’t you just lie down and let the sweat dry until you go to the shower?

In answer to the first question, the cool-down period allows the blood to be gradually redistributed in the normal resting pattern. The body temperature returns to normal. Your heart rate goes back to normal.

The answer to the second question is No. The best procedure is to keep moving for at least several minutes after vigorous exercise. You are trying to get your breathing and heart rate back to normal. You want your body to literally cool down.
Why not just lie down—or sit down—to cool off? An abrupt and complete cessation of the exercise reduces the flow of venous blood to the heart. A complete stop may also decrease the heart stroke volume. The heart may have to work much harder to maintain an adequate blood flow. Thus abruptly terminating exercise may lead to dizziness, fainting, shock, or other strain on the heart. Most heart attacks that afflict older persons in exercise situations take place during the post-exercise period.

The ideal cool-down exercise is slow jogging or walking. At the same time the subject should swing his or her arms. Once the pulse rate has reached about 120—a ten-second count of 20—the re-adjustment has been largely accomplished.
Hot showers, saunas, and steam baths also are not recommended for the immediate post-exercise period. The hot shower, sauna, or steam bath merely adds strain. While they can be enjoyable and relaxing, be sure to wait until the body has returned completely to normal before indulging in them

Ice-cold showers present their own dangers. Ice-cold water flowing over the chest increases the blood pressure. It also raises the heart rate and cardiac output. While a healthy individual can tolerate the additional load, a person with cardiovascular problems could experience difficulties. Such a person may or may not know of his condition; the ice-cold shower would take its toll in either case.

The need to shower after heavy exercise cannot, of course, be minimized. A noted educator once stated that a social gap exists between those who bathe daily and those who do not. The gap would widen if the shower were not a post exercise priority. But the shower water should have a moderate temperature—about 70 degrees. At that temperature, the shower tones the skin while also cleaning.

Some experts recommend a warm shower followed by a cool one. The warm shower opens the skin pores; the cool one closed them. Medical authorities agree generally that the practice has merit for persons in good health.