I am often asked if it is important to stretch.  The answer is a definate maybe.  What that means is that it is an individual choice, but there are a few things to consider.  First, muscle soreness after exercise does not come from “tight” muscles as much as it does from microscopic damage to the muscle fibers.  This happens when we do more exercise than we are used to.  Therefore, stretching is unlikely to prevent or alleviate delayed onset muscle soreness (DOMS) after exercise. 

Secondly, stretching before exercise has not been shown to prevent injury or improve performance (see link).  While there are exceptions, most sports and physical activities do not require stretching before exercise.  Stretching has a temporary analgesic effect (reduces discomfort) and may slightly weaken the muscles for a short time.  The ideal way to begin a workout, whether or not it includes stretching, is with a warm-up.  This means a light activity that gets blood flowing, raises the heart rate gradually and uses the muscles in much the same way that they are going to be used during the workout. 

The third consideration is that stretching may have less impact on increasing range of motion than we think.  Much of our flexibility is determined by genetic factors, age and sex.  Moving that occurs with resistance training and active range of motion is likely to help maintain one’s normal flexibility.  Passive stretching may be a good way to cool down and “reset” the muscles and additionally may feel good.  But it is important to note that it has its limitations and may not be everything we always thought it was.

http://www.acsm.org/AM/Template.cfm?Section=Home_Page&template=%2FCM%2FContentDisplay.cfm&ContentID=4229