Answer:
Posture.
Step-by-step explanation:
Posture is defined as the position in which a person holds his or her body while walking, standing or sitting.
This position can influence the flexibility of the body, improving it or deteriorating it. For example, if a person holds a not correct position, that is, if that person is curving his bag all the time, then those muscles will lose some flexibility, making harder to correct that posture.
Therefore, the right answer is Posture.