Re: Correct Movement in Aikido
Modern sports science would indicate that you would not want to learn or practice to a great degree while exhausted. Your neural pathways develop along the lines they're used, so learning and practicing a technique while exhausted will lead to performing that technique like you're exhausted. You want to build and reinforce the neural pathways while you're fresh, albiet loose and warmed up.
That said, there is a certain, for lack of a better term, spiritual gain that can be made through practicing to and beyond the point of exhaustion.