Original weapon-less kata were designed to be used via a process known as 'contact reflex'.

Contact reflexes are the reflexes of touch rather than vision. Contact reflexes are primary reflexes. They are faster than visual reflexes, so, proper responses in the applications are triggered by contact not by vision. This goes against modern perceptions of martial arts and 'self defence' in which opponents are generally perceived to engage in combat separated by a considerable space - a gap. Authentic kata are intensely concerned with what happens after contact!

The vehicle traditionally used to train contact or touch reflexes is pushing-hands.