In my "career" as a tennis player, and in my years as a coach after that, I have always emphasized the importance of intensity. This aspect of training is essential if you want your efforts to produce results over time.
Personally I have never had a problem with maintaining a high intensity during training sessions. I don’t like wasting time on court, but as a coach I have seen that a lot of my students lose valuable training time by messing around.
Jimmy Connors didn’t spend hours and hours training on the courts, but the time he did spend there he practiced at an almost manic intensity. This intensity involved both his mind and his body – he was fully focused in every aspect of his being. The reason I have posted this article in the psychology section is because mental intensity is every bit as important as physical intensity, if not more so. If you are not fully focused mentally you will not be able to maintain a high level of physical intensity. And as with everything else in tennis, you have to practice your intensity if you want to be able to instantly call upon it in a match.