This article is from the Stretching FAQ, by Brad Appleton Brad_Appleton@ivhs.mot.com with numerous contributions by others.
Stretching is *not* a legitimate means of cooling down. It is only part of
the process. After you have completed your workout, the best way to reduce
muscle fatigue and soreness (caused by the production of lactic acid from
your maximal or near-maximal muscle exertion) is to perform a light
"warm-down". This warm-down is similar to the second half of your warm-up
(but in the reverse order). The warm-down consists of two phases:
1. sport-specific activity
2. dynamic stretching
3. static stretching
Ideally, you should start your warm-down with about 10-20 minutes of
sport-specific activity (perhaps only a little more intense than in your
warm-up). In reality however, you may not always have 10-20 minutes to
spare at the end of your workout. You should, however, attempt to perform
at least 5 minutes of sport-specific activity in this case. The
sport-specific activity should immediately be followed by stretching:
First perform some light dynamic stretches until your heart rate slows down
to its normal rate, then perform some static stretches. Sport-specific
activity, followed by stretching, can reduce cramping, tightening, and
soreness in fatigued muscles and will make you feel better.
According to `HFLTA', "light warm-down exercise immediately following
maximal exertion is a better way of clearing lactic acid from the blood
than complete rest." Furthermore, if you are still sore the next day, a
light warm-up or warm-down is a good way to reduce lingering muscle
tightness and soreness even when not performed immediately after a workout.
(See "4.12 - Pain and Discomfort").
 
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