The Rubber Band Effect
/Human beings are like rubber bands. If you spend all day with people and come home to a crowded house and don't get any days off for months at a time...you will crave retreat and alone time.
And the opposite is true, if you go off in to the woods by yourself for two weeks, you'll be wanting to party.
I've done a lot of food experiments over the years. At one point I was using my programmable rice cooker to make rice porridge (jook, bai jou, congee) every morning. I varied the ingredients a lot. First I would consider the season and the weather, then I would take my pulse and look at my tongue in the mirror. For this time of year I might have ground sesame with a little bit of white fish, salt and a small amount of fresh green onion (scallions). In Chinese medicine this recipe cools the blood while also strengthening it (also recommended for women who have recently given birth). The green onion helps with the transition to Fall, invigorates the qi, and releases the surface of the skin (helpful for staying cool).
But everyday I would change the recipe, perhaps the next day my rice porridge would include roasted pine nuts in chicken stock (Tonify qi, calm wind). The variations were infinite but for about a year I was very strict that every morning I ate rice porridge of some kind.
The results were great, my digestion was wonderful, I loved it. The problem was the rubber band effect. I couldn't go out to eat without feeling terrible the next day. It all came to a head when I went to visit my sister in Seattle. We had pad thai and something else fried two nights in a row, and breakfast was whatever, eggs, toast, cereal. My tongue turned black. I felt terrible. My body was craving the regularity I had taught it to expect. I realized that although I could get great results from strictly regulating my diet, it also made me really inflexible about what I could eat.
The rubber band effect is important for understanding stretching and flexibility. If you stretch a lot in one day, you are likely to wake up tighter the next day. I've known many yoga teachers who were really stiff when you met them for tea on a foggy afternoon, but in yoga class, after a warm-up, they could get into some serious pretzel shapes. This is one of the differences between internal and external flexibility. Internally flexibility is available all the time, external flexibility requires a warm-up. (Bikram Yoga is the worst because they super heat the rooms, making the rubber band effect even stronger.)
I've found that I can reduce the rubber band effect by gradually increasing my stretch over a week or two so that the change doesn't happen all in one day. But the long term results will still be external. Internal flexibility is just a different animal.
So you might now be wondering, can I have both internal and external flexibility together?
To answer that question I should start out by saying, some people are naturally internally flexible. It is rare, but I have a friend in Australia who can do the splits anytime, anywhere, and I lived with him for a while so I know he never stretches. I've also known a few people who were naturally externally flexible, their joints are always loose because their ligaments are long. These people (mostly women) are 'floppy' and often want to develop muscle tone in order to simply hold themselves together. They really don't need to stretch but sometimes find themselves in jobs as Yoga teachers or even contortionists because it's so freaking easy for them.
Chinese have traditionally given a lot of attention to training people before puberty because the body you have during puberty is remembered as kind of a stable state. It is what you will tend to rubber band back too if you have enough exercise, qi, sleep, and a modest diet. If the body you had through puberty was flexible, you'll tend to find that flexibly easier to keep or to recover.
Now that I've got that out of the way, the answer is yes, you can have both internal and external flexibility in the same movement. It just requires that you don't create the rubber band effect by stretching past your internal threshold.
Many martial arts teachers teach stretching routines like 'chin to toe.' I believe that some of them are both internally and externally that flexible. I don't want to give the impression that internal flexibility is permanent or that it requires less of a time commitment. Like my external flexibility, my internal flexibility changes from day to day. For instance, after getting sick for a few days my internal flexibility can shrink down to almost nothing and I'll feel internally tight.