This is a question we hear often. As tennis conditioners, we've worked with many top athletes. One thing that always stands out among professional players is that when they workout for tennis (off-court), they push even harder than they would on-court.
Lleyton Hewitt, Sam Stosur, and Martina Navratilova are great examples. When we trained them, they always knew when to bring a high level of intensity.
Training at high intensity is how players allow their bodies to work equal to and above the thresholds faced during competition.
Through rest and recovery, their bodies adapt and improve, allowing them to push more as they develop. Without this adaptation process, there are often minimal or even no physical gains.
When training out of competition you are basically preparing for competition and not just training for the sake of it. This is critical, as training is about preparing the body. It's imperative...