Final answer:
The optimal level of arousal for training a dog is Eustress, which is a moderate level of positive stress that enables the best performance without causing distress or relaxation.
Step-by-step explanation:
The optimal level of arousal for training a dog is when the dog is in a state of Eustress. Eustress is a positive form of stress that leads to optimal performance, as it helps individuals feel fully energized and focused. This is in contrast to distress, which is excessive and debilitating, and relaxation, which might be too low for optimal learning and performance. As such, the optimal level of arousal for both humans and animals like dogs for performing tasks effectively is not a state of extreme calmness (relaxation) nor is it one of high stress (distress), but a moderate level that facilitates concentration and learning.