Answer:
Sympathetic nervous system.
Step-by-step explanation:
The sympathetic nervous system prepares the body for the “fight or flight” response during any potential danger. The sympathetic nervous system (SNS) increases heart rate. A faster heart rate (usually) pumps more oxygen-rich blood to the brain and lungs. This can give you the energy to run.
While you are waiting to begin a foot race, you can feel your heart race go up. This is the sympathetic nervous system at work.