Training is not just about the methods themselves, it's also affected by the health and state of mind of the dog. (barktodaytraining.com)
However, it is important not to go overboard: The mind of a dog is roughly equivalent to that of a human who is 2 to 2 1/2 years old. (discovermagazine.com)
Working the mind of your dog is just as important as exercise. (mcleanvet.com)