Answer: Dynamic equilibrium.
Explanation: When a person is running on a treadmill, they are in a state of dynamic equilibrium. Dynamic equilibrium occurs when a system is in constant motion and the forces acting on the system are balanced. In this case, the person is in motion (running on the treadmill) and the forces acting on them (gravity and the force of the treadmill belt) are balanced, allowing them to maintain their motion at a constant speed.