If you've ever been surprised by an unexpected loud noise, you've experienced the startle response. Your shoulders come up, neck forward, head back and down, abdominal muscles tighten mightily, hands clench, etc. (Here's a picture). Somehow, your nervous system has prepared you for flight or flight, all in less than 75 milliseconds. Pretty fast. And that's good, provided there really is a threat to fight or flee from.
But the problem, as I wrote about in Taking Moshe to the Movies way back in 1995, is that this bodily startle response pattern can hold on and on and on way after the initial stimulus. This body pattern of stress and anxiety can cause lots of problems if it's held when not needed. "Choking" during athletic performance is one unwanted consequence. The pattern also shows up in folks with excess responses to anxiety; Startle response in people with Post Traumatic Stress Disorder (PTSD) is a good in depth look at how the pattern operates in PTSD.
The bottom line here is the unnecessary startle response pattern hinders how we perform activities, compared with the times when we don't have it. But to do something about it, we have to recognize that we are in it first. Then, various movement education tools can helpful in releasing it, at least temporarily. I'll be exploring this in more detail in the future.