Cooling down means that after vigorous exercise, you move far more slowly for several minutes before you stop exercising for that session. The only known benefit of "cooling down" is to keep you from feeling dizzy or passing out after very vigorous exercise. However, cooling down has not been shown to:
• reduce next-day muscle soreness (J Hum Kinet, Dec 2012;35:59-68),
• help you to recover faster so you can compete sooner or improve flexibility (J Hum Kinet, March 2012;31:121-9),
• improve fitness level,
• make you stronger (J Strength Cond Res, Nov 2012;26(11):3081-8), or
• prevent injuries.

Exercise-Associated Collapse
Most cases of exercise associated collapse are caused by stopping suddenly. After a long race, you should slow down gradually. Cooling down prevents feeling faint and passing out. Exercise-associated collapse is the most common reason that athletes are treated in the medical tent following an endurance event. It is caused by the loss of muscle pumping action caused by suddenly stopping exercising. On the other hand, when a person passes out during a race, it can be caused by a more serious condition that can kill a person, such as a heart attack, irregular heartbeats or heat stroke (Physician and Sportsmedicine, 2003;31(3):23-29).

Postural Hypotension
At the end of a marathon, a runner sprints over the finish line, falls down and lies unconscious for a short time. What’s the most likely cause? The possibilities include dehydration, hyponatremia (excessive fluid intake with too little salt in the blood), heat stroke (a sudden uncontrolled rise in body temperature), drunkenness, a heart attack or stroke. Usually it is none of these. Almost all athletes who collapse after finishing a marathon suffer from postural hypotension: lack of blood flow to the brain because blood drops from the brain to the legs. Treatment is to lie the person on his back, raise his feet high over his head and wait for him to revive. If he or she is not alert within seconds, you should consider the more serious causes of unconsciousness and get medical help immediately.

Professors at the University of Capetown in South Africa analyzed data on runners who collapsed during an ultra-marathon (Medicine and Science in Sports and Exercise, Sept 1994;26(9):1095-1101). Most cases occurred after the runner crossed the finish line. The few cases of collapse away from the finish line were caused by diseases such as asthma and heart damage. Most cases of collapse occur in runners near the cutoff time for an award. All of the runners who collapsed had an excessive drop in blood pressure when they went from lying to standing.

Mechanism of Passing Out
During vigorous exercise, your legs drive your heart, your heart does not drive your legs. First, your leg muscles contract and squeeze the blood vessels near them to pump blood toward your heart. Then the increased amount of blood returning to your heart stretches the heart and causes it to beat faster and with more force. Then your leg muscles relax and the veins near them fill with blood to start the next cycle. When you run fast, your leg muscles do a considerable amount of the work pumping blood through your body. If you stop suddenly, the blood pools in your legs and your heart has to pick up the slack. At the end of a long race, your heart may not be able to pump more blood, so not enough reaches your brain and you end up unconscious. Cooling down will prevent this.

Cooling Down Does Not Prevent Next-Day Muscle Soreness
Some people believe that cooling down gets rid of lactic acid so that you will recover faster for your next competition or training session, but this is not true. Lactic acid build-up lasts only for a few minutes even if you do not cool down. Muscle soreness after exercise is not caused by lactic acid; it is caused by small tears in the muscle fibers.

Checked 11/2/17