Playing tennis or operating in any strenuous physical environment is best accomplished with activity specific conditioning. As you age, it becomes even more important.
Here is a quick list of items you might consider for Tennis.
Morning pre-breakfast workout.
My first intake of the day is coffee and whatever initial supplements I take such as fish oil, Vitamin D, and a multi. I get no food until my first strength and flexibility workout. It's a deal I make with myself that considers eating a reward after the effort required to get through the 30-60 minute workout.
First effort: Inversion table
The inversion table doesn't have to be a static stretch of your spine. While you are upside down or at whatever angle of decline you put on your spine for disc decompression, you can still do other things with your hands while upside down.
I use an assortment of fine motor skill repetitions to use the upside down time efficiently. If you're involved in any sport that requires hand grip strength and dexterity there are a grip devices you can use. These include grip strength trainers, finger strength trainers, and stress balls. Use whatever you want but use the time to accomplish something that will improve your grip strength, finger dexterity, and endurance.
Second: Curls
Using light weights like a 10lb or 15lb kettle ball I go for reps on both arms, one at a time. I go until my arms are done, and then move to a heavier one for fewer reps.
Third: Pullups and Chinups
A Pull-up/Chin-up bar in a door frame allows for shoulder and upper body use. I don't have to lift your full body weight initially or ever to get some value out of this. I use my feet to give an assist since I have some injuries that age has told me won't ever fully recover. That doesn't stop the ability to use half weight limited-range-of-motion pull-ups and chin-ups. I won't hurt myself if I choose more repetitions and less weight and range of motion to get maximum benefit.
