Re: True Internal Strength
(modified from a post on the QiJin forum)
Pretty much all the Asian martial arts use or previously used some degree of qi and jin (ki and kokyu) skills. So to call jin or suit stuff "internal" is not accurate unless you specify that it has to do with "internal strength" ("nei jin" in Chinese). Both "internal styles" (nei jia) and "external styles" (wai jia) have "nei gongs" ("internal exercises") that develop "nei jin".
When someone says that Taijiquan, Xingyquan, Baguazhang, Wujiquan, Liu He Ba Fa, etc., are "internal styles", the general inference points to the fact that they use the dantien as a major motivator of all movements and the "six harmonies" natural winding of the body is present. The problem is that there is no clear line, in many cases, where some style fully or partially or not-very-much uses the dantien.
In a case I was talking about to someone in p.m., I noted that a certain Taiji person actually had a strong Bajiquan (fairly linear, but very powerful) way of moving. But Baji is a so-called "external martial art" and Taiji is an "internal martial art", so what the crossover highlights is that the basic qi and jin skills are common. The mode of movement is different enough that just about anyone with a modicum of experience can spot the Baji dominance in a supposed Taiji expert.
In Aikido there is a similar problem. Watching Ueshiba perform some swordwork in the 1930's (on film) I could see that he had more idea of store-and-release than I would have thought. And because movements get smaller with practice over the years, it's a hard thing to pick up in later films of him. I've never seen Tohei do this sort of thing even though I've watched many films very closely; in my opinion Tohei does not know how to do them. So the point I'd make is that there is a potential disparity between Ueshiba's use of the dantien/hara and that of Tohei. It's enough of a disparity that it's similar to the "internal" versus "external" discussion in CMA's. So what's the correct mode of training for Aikido?
If my evaluation of Ueshiba's movement and knowledge is correct, then Ueshiba used backbow and dantien in a whole-body method that was different from Tohei's more linear use of qi and jin. Both Ueshiba and Tohei used the soft-repetition method of developing suit to augment their jin, but I suspect that Ueshiba's training was probably more vigorous and broad-spectrum, overall. I don't think that either of these men used any of the more Shaolin-derived methods of extended tension and "squeezing" conditioning, that I see offered as substitutes for Ueshiba's qi and jin development methods. I.e., I tend to suggest people do a little thinking about exactly the mode of training that was used originally.
There are a number of methods to train "nei jin". Traditionally, the extended postures, "structure", dynamic-tension, etc., approaches are more from the "external" modes. The softer approach of jin training accompanied with breathing/suit training are going to mark the "internal styles". Being extraordinarily strong and conditioned though isn't going to handle the question of just how "wholebody" a method is, nor does it address the question of how dominant is the control of the dantien/hara. As I've said before, there are many levels and gradations of these skills.