Why is it important to stretch before doing physical activity?

It is better to stretch after lifting weights.

from "Why Should I Stretch After a Workout?" by Summer Cavalier-Banks,

"Stretching after a workout serves a dual function. The body is given time to cool down and the muscles are elongated after shortening during the workout. Stretching is essential for muscle health and the prevention of injury.

When a muscle is used repeatedly, lactic acid moves into the muscle. This is the acid that causes pain in the muscle after a workout. When the activity stops, the muscles are at their shortest and need to be stretched while warm in order to move some of this acid out of the muscle. When lactic acid is left in the muscle, contraction can occur and the muscle can be injured easily.

The Proper Method of Stretching

Stretching is an easy exercise, but many people still perform stretches incorrectly. When the muscle is warm, is should be elongated with a smooth and even movement. Bouncing and forcing the muscle to stretch farther than a natural movement can cause tears in the muscle.

Stretching should be used for every muscle and after every workout routine. This includes weight training and cardio. After cardio exercises, stretching should focus on the larger muscle groups of the lower body. These include the muscles on the front of the thigh, back of the thigh and lower legs.

Weight training exercises can include every muscle of the body and while it may be impossible to stretch every muscle, the major muscles of the area should be stretched. When lifting weights with the upper body, for instance, the biceps, triceps and chest muscles should be stretched after the workout.

Stretching helps prevent injury and reduce pain, but also serves a third purpose. If the muscles are not stretched, the lactic acid can leave a person feeling like they do not want to work out again. The pain may be too much to move the muscle group and that can lead to a reduction in physical activity." - http://www.associatedcontent.com/article/2188885/why_should_i_stretch_after_a_workout.html?cat=51 accessed on April 13th, 2011