Arousal
So it turns out there is a law that correlates the metal/physical arousal and performance. The Yerkes-Dodson law is an empirical relationship between arousal and performance. The law outlines the fact that with increasing mental and or physical arousal there is increasing performance, but only to a certain point. From this point forward there is less and less return. Depending on the task, the level of arousal that is optimal is variable. It is graphically represented as such.
The 2 main critiques are that overlearning should predict improved performance in states of high arousal and both performance and arousal and presented as singularities while in reality they are multidimensional.