Refer to figure.
Arousal and Performance
Arousal is the measure of the human being's readiness to respond.

The relationship between arousal and performance is a symmetrical inverted U (performance being on the vertical axis and arousal on the horizontal axis).

Increases in arousal will result in the increase of performance, up to a point, called the break point, beyond which further arousal is dysfunctional to the outcome of performance. At the optimum arousal level, we are at our most efficient - optimum arousal happens just below the breakpoint