The third major stretch of the basic ten stretches of Isaka Sensei's sit down practice is easily understandable, and very easy to cheat on as well; it's the sit down Yoko-geri stretch.
There are a number of points that are quite a challenge to this stretch. The main thing is beginners should never overdo it. The second main thing is that the stretch actually should occur in two places; one is obviously using the floor and your body to lever the leg to introduce flexibility to the hip. The second though is within the pelvic girdle, actually helping to ease a stretch inside the pelvic girdle, using the non-extended leg.
N.B.: It's very easy for youngsters or well meaning people to do things like stand on the hip that's being extended. As well as being anything from painful to excruciatingly painful, doing this can be really damaging and dangerous. Don't ever fool around with this stretch!
Dos and Don'ts with and the Inside Story with Sit Down Yoko-geri
The key things are; keep your back straight and don't lean forward- i.e. cheat. Also, push the leg out gently from the hip. Imagine the feeling of pushing the leg out along the floor is one of the most important parts of loosening the hip. Remember, this is not a stretch so much as loosening (cutting the chains as IS puts it) of the hip.
Now we get to the less obvious but very important stretch: the position of the non-kicking leg is very important; if you can, you should keep the heel in front of the center of your hips. Just like a perfect Tobi-geri! Just like Yahara Sensei!
Top Tips: (No relation to Viz)
Do lean into to the "kick" and if you are up to it, get a partner to GENTLY either push you a little or pull you a little. But the partner should never force you. If you are a beginner or very stiff, it is likely that you will have to practice this for a few months before you can even begin to appreciate just how good this stretch feels!
The next big thing is the toes. Or "TOOZ" as Koike Sensei always used to call them! (:-) It is vitally important to keep the sokuto correct in order to (also) stretch all the tendons and muscles in the leg, but what will really bring out the best is keep the toes pointed up!
If you are feeling really advanced, then you can also finish off the stretch by then lifting the heal up as well.
Remember, don't try to force the leg out and your position to the vertical; relax and imagine it and gently work toward it remembering to breathe and relax.
Hope you are already getting the "special feeling!"