When the muscles are warm, they are more flexible. Stretching them at this point can improve range of motion and accelerate recovery. More specifically, stretching right after a run can help reduce muscle and joint stiffness that can occur post-workout, known as delayed onset muscle soreness (DOMS).(Nike running)

Any exercise that involves the use of your stomach muscles and back muscles in a coordinated way counts as a core exercise.(mayo clinic)

Having a stable core is an essential part of any runner’s toolkit. By building your core muscles, according to experts, you can enhance your performance, decrease lower back pain, and even avoid common running-related injuries.(Runner's world)