Board Thread:Theories and Speculation/@comment-1872728-20160305150743/@comment-26369387-20160325195355

To quote Chakra-article:

''Chakra is created when two other forms of energy, known collectively as one's "stamina", are moulded together. Physical energy (身体エネルギー, shintai enerugī) is collected from each and every one of the body's cells and can be increased through training, stimulants, and exercise. Spiritual energy (精神エネルギー, seishin enerugī, English TV: Mental Energy) is derived from the mind's consciousness and can be increased through studying, meditation, and experience. These two energies becoming more powerful will in turn make the created chakra more powerful. Therefore, practising a technique repeatedly will build up experience, increasing one's spiritual energy, and thus allowing more chakra to be created. As a result, the ninja is able to do that same technique with more power. This same cycle applies for physical energy, except the ninja needs to increase their endurance instead.''