“Pre-race jitters are a very common, expected aspect of competing, and all athletes experience them to varying degrees. They are a manifestation of processes occurring in the body which prepare it for action — the “fight or flight” response. The sympathetic nervous system (SNS) is the part of the body responsible for the symptoms that an athlete experiences, and epinephrine (“adrenalin”) is one of several hormones released into the bloodstream. The goal of this nervous system activation is to help the body achieve peak performance and is a survival mechanism.
Some of the specifics of the SNS response include improved reflexes, enhanced memory, regulation of blood flow, and a switch to a catabolic state. The latter causes fat stores and liver glycogen to be broken down. This insures a steady stream of fuel — fatty acids and glucose, respectively — for the heart, muscles, and vital organs.
The downside of SNS activation is that it causes a series of annoying symptoms. Diarrhea, intestinal cramping, tremors (“shakes”), sweating, palpitations, nervousness and irritability are some of the distractions that an athlete may face. Sometimes these symptoms may become so great that they go beyond the nuisance stage and performance suffers.”
This comes from an article written by Mark Jenkins, MD in 1998. After the above introduction, he goes into mechanisms that athletes can employ to manage these situations. Here’s the full article.