Gozo Shioda Sensei's words

"As you grow older,your muscles weaken,and you can't lift or pull as when you were young. This kind of power is limited and it cannot help but decline no matter how much you try to build it. So, as Ueshiba Sensei said, the key to unlimited strength is "Kokyu Ryoku", Breath Power. It is, in fact, based on natural principles. When your opponent tries to use his power against you,you can simply absorb it into your own.Therefore,you don't need use any force yourself." 
 
" Aikido is said to be the martial art of 'Wa', Harmony. It is not difficult to explain this. When you see your opponent, you posess both a personality and power which makes your opponent feel that he doesn't want to fight with you. This becomes 'Wa'. It does not mean that you compromise. 'Wa'is only possible when you have "something strong" within yourself, that makes your opponent your friend, and makes them cooperate with you. This is called, "Tai sureba ai wasu", which means, 'When you see your opponent you harmonize.' This is only possible when you have "Toku", Virture, the foundation of which lies in your "Chu Shin Ryoku", Center Power."