The Importance of
Recovery and Cooling Down After a Race or Workout

You have just had a good workout or just finished a race.  You are tired and just want to go home or get something to eat.  This is how everyone feels, but you need to give your body a chance to recover slowly.  Many athletes have a pre race check list that they follow to the letter, yet fall short when it comes to cooling down. This is the main aim of the cool down is to promote recovery and return the body to a pre exercise, or pre work out level.
That discomfort ("post exercise muscle soreness, tired legs"), is caused by a number of things.
Firstly, during exercise, tiny tears called micro tears develop within the muscle fibers. These micro tears cause swelling of the muscle tissues which in turn puts pressure on the nerve endings and results in pain.
Secondly, when exercising, your heart is pumping large amount of blood to the working muscles. This blood is carrying both oxygen and nutrients that the working muscles need.  When the blood reaches the muscles the oxygen and nutrients are used up. Then the force of the contracting (exercising) muscles pushes the blood back to the heart where it is re-oxygenated.
However, when the exercise stops, so does the force that pushes the blood back to the heart. This blood, as well as waste products like lactic acid, stays in the muscles, which in turn causes swelling and pain. This process is often referred to as "blood pooling."

So, the cool down is important as it helps all this by keeping the blood circulating, which in turn helps to prevent blood pooling and also removes waste products from the muscles. This circulating blood also brings with it the oxygen and nutrients needed by the muscles, tendons and ligaments for repair
It is fairly simple, when you train/race you strain your muscles, in doing this you cause a greater volume of lactic acid to build up in your muscles, you cause microscopic tears in the muscle tissues, and dehydrate the muscle of important fluids.
After exercising, and following the cool-down period, the athlete's heart will still need a period of time to settle back down to its full resting rate but should be within 30 beats of what it was before the exercise session started. This will, of course, be influenced by the overall physical condition of the individual. It may also be influenced by the content of the session, with more demanding sessions requiring a more extensive cool-down.

What should I Do?

Clothing – Sweat Suits
Staying warm after a workout or a race in important as it keeps the muscles more receptive to stretching. Letting the body get cold to fast can be harmful, so no matter the weather one should put on clothing to keep the muscles warm.

The Ice Bath - Hydrotherapy
Much of the discomfort after a race or workout is caused by a build-up of lactic acid in the muscles, the best thing to do is to take an ice bath or fill up the bath with enough cold water to immerse your legs in it. The cold water causes the muscles to contract and expel the lactic acid. The cold water bath has been recommended by and famous distance runners, sprinters as well as coaches.

Then there is the question of what to eat or drink after the run. If your muscles are lactating badly, it might be a good idea to take some sugar based drink. Aside from that, the main priority after the race is to get protein into the system to help the body's regenerative systems. If you're not feeling too much like solid food, a shake can be ideal - bananas, protein powder, and juice.
If you have perspired a lot during the run, you might also be short of certain electrolytes like magnesium or potassium that are also essential for muscle recovery.

Running and Stretching
This is the time of importance. It is the time to bring the heart rate down slowly a long slow run of 15 minutes to 30 minutes will do the trick.  The inclusion of stretching exercises within the cool-down period not only helps to gradually lower the activity level of the body at the end of the session, but it may also prevent stiffness the following day.