Your muscles strengthen
Running affects every part of your body and not just your lower body muscles. The more pronounced effect is how it activates the glutes, the powers of the thigh, calves, and feet. But it also has a significant impact on your abs and back. Running requires different muscles to work together as they adapt to the demands you place on them, depending on how intense your training session is. It is most advised that you start with short distances and gradually increase them. Your muscles can adapt, and your workout is more effective.