The January 2009 issue of Men's Journal magazine has an article on resistance stretching as well as a guide to some of the stretches. You can go to the Innovative Body Solutions website here to read the article online. Just find "The Better Way to Stretch" article on the front page and click on "read the article". This is the website where you can also buy the "Resistance Stretching with Dara Torres" DVD, a very worthwhile and inexpensive investment if you are interested in learning how to do resistance stretching.
One thing I learned from the article is that there are two different types of muscle tightnesses according to Andy O'Brien, the strength and conditioning coach of the Florida Panthers hockey team. He says there is "adaptive shortening" of the muscles due to scar tissue or injury. He's says this is a permanent shortening of a muscle. It doesn't say it here, but I guess this is where you may need a therapy like active release technique (ART) or something I have never tried called the Graston Technique. The other type of shortening he calls "tonic shortening". This would be when your muscles get tight due to excessive work, like running a marathon or a hard workout. In this case it is your nervous system tightening up your muscles and thus your range of motion. He suggests that resistance stretching helps you to train your nervous system to relax and thus it allows you to be more flexible.
Here are some other posts I have made on resistance stretching.
My Top Two Recomendations to Help You Recover Your Stride
Resistance Stretching: This is what Dara Torres does!
More on Resistance Stretching
The Genius of Flexibility Video 1.0 Review
More on the Dara Torres Resistance Stretching DVD
The Growing Influence of Resistance Stretching
SNAP!!! What in the World was That? OK don't stretch too hard!!!
Hold Steady and Stay Positive After getting stretched by a professional.
Partner Resistance Stretching
Improving a Hamstring Stretch
A Recent Article and Video on Resistance Stretching
This is the only book I know on Resistance Stretching.
You can get the Dara Torres "Resistance Stretching" DVD at Amazon.