After a conversation with my coworker Jonathan Welch, who is starting to lift weights again, I realized the importance of stretching might not be common knowledge.
Jon’s arms and chest were seriously sore for the previous day’s workout with free weights and I suggested to lay back on a swiss ball to stretch the muscles on the front of his chest. He then asked a great question, “Does it make sense to stretch the muscles if you are trying increase the muscle mass?”
Stretching muscles after toning exercises is crucial unless you are going for the hunched over, and immobile look. The physiological changes that occur when exercises are complex but here is the simple picture. In order to build muscle the fibers must first break a little and then rebuild. This is part of the reason why muscles get sore. You are actually producing micro tears in the body of the muscle. If you continue to exercise regularly, the repaired muscle fiber layers increase, which in turns increases the size of the muscle and the power behind it.
Contracting a muscle while lifting weights shortens the muscles. Stretching prevents the muscle from staying in that contracted state. While it’s true that the contracted muscle is often what body builders are looking to gain, it definitely puts a damper on your flexibility. While it’s true there is a little bit of an either-or in the ratio of flexibility vs. strength, (as in you can’t get maximum strength and maximum flexibility at the same time), I would assume the average person doesn’t want to sacrifice mobility for brute strength.
Anyway, this is all very generalized, if you are interested in the science of muscles this site is a great place to start. Brad Appleton’s document, Stretching and Flexibility, is full of great information for beginners on the subject.