The two body/mind concepts of Japanese Martial Arts.
In the history of Japanese martial arts there has always been a cultural view of mind and body which puts into perspective the western view of that being 'new'.
So when Tohei presented mind and body co-ordination it was only new really to those outside of Japan. So that's an intro for you.
Then we come to the concept of Hara. Once again always been there in Japanese Martial Arts and was considered where you keep your Ki or spiritual centre.
Now this could be called whatever other name you like form china or wherever, dantien etc. The medical ways of Japan dealt with energy paths and no doubt originated way back in china and acupuncture so also included energy balancing and thus the concepts of yin and yang.
I say all this to give you a picture of Japanese and what was common to Japanese and held by them as normal Japanese ways.
So now to tell you about the second body mind concept of equal importance and significance to the Japanese. Once again very normal and cultural and widely known throughout their history. This second mind body concept was common knowledge. I say this also so that when you consider O'Sensei and Aikido it would be obvious to the Japanese what was expected of them yet to westerners they would need to be told. Thus I feel this second concept has been missed by most westerners.
The second concept is Koshi. The second centre. So for Japanese they were used to using two centres so to speak.
Luckily for those who did Toheis Aikido where they developed weight underside they were in fact learning about Koshi.
Koshi is the back of the hips, translating as the lumbar pelvic centre. Just near the base of the spine.
This in Martial Arts goes back to the origins of all Japanese martial arts. The Hara was the spirit centre and Koshi was the pivot from where you moved. Keep ki in your centre and move from koshi is standard procedure.
Thus the centre of so called 'ground force' in Aikido terms or Japanese is Koshi.
Now I'll leave you with my own personal advice. Connect to heaven with Hara and earth with Koshi.
Hope some find this interesting.