The first 10 minutes I'll warm up by hitting very lightly. At the 20 minute mark, I'm swinging with more speed but still focusing on consistency over power. At the 30 minute mark, I've got my strokes down. The next half hour will be my best. All my strokes and footwork are good. As soon as one hour of all this is done, something just "snaps" and I'm playing like crap. I'm just mostly inconsistent. One theory I have is that I just get mentally lazy. I'm not out of shape, I just feel mentally tired. Is there any way I can prolong the "golden tennis" time period, past the 1 hour mark?