Here is one of our Senior Tennis players, Dr. Mark Frisk training with Paul Pisani in Ponte Vedra, FL.  Mark is one of the top 45 year old players in the country and takes his tennis and training very seriously.

Here is one of the lower body exercises that we did yesterday.  As you can see Mark is using his core, quads, glutes, and hamstrings in this one exercise.  

I recommend starting at a very low height of 6 inches, and working your way up to a height like this.

This will also elevate your heart rate, giving you an excellent cardio effect.