In order for a person to become more flexible, he or she must increase the range of motion at a joint by not just elongating a muscle, but also by making connective tissue in (elastin and collagen ("Glossary") and around (tendons and ligaments ("Glossary") a muscle more elastic.
To do so, a person should use the FITT principle to improve flexibility.
Stretching should be included after every workout to encourage improvement and maintain overall flexibility.
The ACSM recommends flexibility training a minimum 2 to 3 days per week.
Stretching should never be painful. The focus should be on bringing the muscle to a point of slight tension.
The ACSM recommends that each stretch should be held for 10 to 30 seconds to mild discomfort; 3 to 4 repetitions per stretch. On a PNF stretches ACSM suggests a contraction for 6 seconds followed by a 10 to 30 second assisted stretch.
The length of the flexibility component depends on the needs/time constraints of the person. In most cases, flexibility training should last at least 5 to 10 minutes. Stretching is one area of the workout that tends to get cut short when time is running out.
OPTIMAL TIME TO STRETCH
The BEST time for a person to stretch would be right after a workout, when the muscles are very warm. Stretching prior to exercising is really not necessary. It does not prevent injuries and may lead to cooling down. Dynamic stretching can be used and is encouraged to be used as part of a person's warm up prior to exercising with static stretching to be used after the workout to improve range of motion at targeted joints.
WARMING UP
Dynamic Warm Ups are the best way for your body to prepare for exercise. If you are not warmed up for a workout, you increase your chance for getting an injury during the workout. For a nice summary (and interesting read) about dynamic warm ups (it has a nice video to show you what he is talking about), go to this page...
Click Here for dynamic warm up page
The video and Warm up used is for heavier exercisers, but about half way down the page in a section entitled "Um, your warm up is tougher than my actual workout!", you can see a less intense example.
You could also do a 3 minute jog and then do the exercises shown in the video on this page... Click Here for Dynamic Stretches
SAFETY
To ensure that when you engage in a stretching routine, please go to this webpage...