Greater flexibility gains can be had by stretching after a workout. A very important, but often overlooked time is to stretch the antagonist and any hyperactive muscle prior to a certain exercise. For example, I was just working with someone who has tight semimembranosus and semitendonosus. They are too active when he squats so I had to massage and stretch those so that they would be inhibited. Now the correct muscles will fire when he squats. The purpose of stretching the antagonist muscle before is to improve the neuromuscular firing to the agonist muscle. Before my clients perform rows I have them stretch their chest. This allows greater ROM in the shoulder and for the the chest not to be tight and prevent as much firing in the rhomboid muscles and other scapular retractors.
I recommend stretching after a workout out for approx. 10 mins.
Static stretching prior to a workout with “cold muscles” is not wise
as you are at risk of injury or muscle tears. A 10 min. cardio warm up should be done…pick your weapon of choice (treadmill, elliptical, bike) and /or joint mobility warm up, gradually increasing the intensity to about 70%