Why does an athletes heart rate increase befoere the race?

An athlete's heart rate increases before a race due to the body's anticipation of physical exertion, triggering the "fight or flight" response. This response is mediated by the release of adrenaline, which prepares the body for performance by increasing blood flow to muscles, enhancing oxygen delivery, and boosting energy levels. Additionally, anxiety and excitement can further elevate heart rate as the athlete prepares mentally for the competition.