Does stretching (before or after) actually affect your workout?

Answer 1

Yes.  Stretching before exercising limbers up your muscles and helps to prevent injury during your workout. Stretching after your exercises helps you to cool off and helps to prevent stiffening later on. Don't neglect your stretches or you could end up seriously harming yourself!

Answer 2

In 2002, a report was published in The British Medical Journal which publicised the findings from medical and academic research with regard to stretching before and after exercise to reduce injury risk and muscle soreness. The report's conclusion was that stretching made no difference.
However, even should the controversial report's findings prove to be correct, warming up or stretching before exercise is as much about preparing mentally as physically. Gently easing yourself into physical activity allows time for focus and mind visualisation which for many people leads to enhanced performance.
Furthermore how you stretch has an impact. Short, bouncy stretches are more likely to cause small muscle tears and soreness due to a body function designed to prevent injury known as the myotatic stretch reflex. When a muscle is suddenly stretched, the body instigates a counter-action to prevent further muscle stretch, holding the muscle at a set length. If you hold your stretches this reflex relaxes and allows you to stretch further, increasing flexibility and therefore often allowing enhanced performance.

Answer 3

It is actually best to stretch AFTER a workout when your muscles are warmed up. Muscles are more flexible after they have been warmed up and can help in increasing your range of motion.

Some people may benefit from doing dynamic stretching exercises before working out (this is not ballistic stretching). Static stretches should be reserved for after the workout or at least after a good aerobic warm-up.

There is a new study on runners that found that static stretching before running reduces running economy and performance. So if you want to run slower than you usually do, stretch beforehand.