Toxins:
As you workout, your muscles produce waste products (toxins). For these toxins to exit the body, they need to be pushed into the lymphatic system. The lymphatic system runs along side your blood, however, unlike your blood, it doesn't have a pump. Instead of a pump, the body uses the movement of your muscles to push the lymphatic fluid towards lymph nodes where the toxins are cleansed. There are lymph nodes throughout the body; behind the knees, in the groin, armpits, behind the ears etc. The toxins eventually flow into your blood stream and are cleansed by your kidneys and excreted out of the body in urine.
So, how is this useful? Well, after a run, instead of coming to an immediate stop, use the last 3-5 minutes to slow down from your run pace to a steady walking pace. This will act as your cool down and flush toxins out of your body.
A reduction in the toxins in your muscles, will help improve how your body feels post workout.
Blood Pooling:
Have you ever felt light-headed after a very intense run? This may be a 100m sprint or a 10km run. Your initial reaction is for your body to stop what it's doing, sit down and try to get some composure back.
However, this could potentially result in you feeling worse, rather than better.
As you run, your heart rate increases to pump your legs full of oxygen rich blood. This allows your legs to keep moving, which in turn aids the movement of blood back to your heart (venous return). As you come to a stop, your heart rate rapidly decreases and you are no longer assisting venous return. This is called blood pooling.
Therefore, rather than come to an immediate stop after running, consider gently returning your heart rate to normal (60-80 bpm is the average for a healthy person) over a period of 3-5 minutes.
Static Stretching:
Flexibility is the foundation of exercise. If you cannot move, you cannot increase your endurance, strength or power. These 4 elements make up the pillars of exercise.
As you run your muscles are continuously contracting and expanding. As you lift your knee up, your quad is contracting, as your knee descends, it is expanding and lengthening. This motion results in changes being made to the muscles and over time an increase in endurance, strength and power occurs.
When you stop, the muscles are adapting to help you the next time you go running. As part of this process, you may feel you have less mobility after a run than you did before a run. To ensure that you maintain your functional range of movement, you should hold stretches for 15-30 seconds on each muscle group post run.