When looking for a reason for lack of motivation to run, it is necessary to understand the role of the invested-received relationship, which is implanted deep within our limbic system.
The relationship between what you invested and received defines an action or decision's effectiveness and determines our relationship to the outcome. In the past and the development of the human species, a high enough efficiency was necessary to make it possible to survive. Evolution and entropy erase inefficient systems and elevate more efficient ones. The effectiveness of movement was key to survival. Therefore, more effective movement is felt as pleasant and good, while the inefficient movement is felt as uncomfortable and painful. As a child grows up, he learns to be tidy and thus improves his efficiency. When he is effective enough to cope with current demands and burdens, curiosity drives him forward.