Which factor most closely defines the body's ability to change direction

You didn't provide us with a list of factors that influence and define the body's ability to change direction. However, a good perceptive/sensory system (being able to hear, see, and smell good) helps us decide on which was we're supposed to move in the next sequence of movements. This, coupled with an active motoric system then provides us with the necessary and optimal tools for changing direction. 

A. vitamin c is your answer