Tennis itself is a great conditioner. In fact, if that's all the time you have then do it. But it also can take a toll on your body if you constantly play and don't let yourself recover. Especially if you have a flawed fundamental. Today I'm going to list alternatives to on court training that improve your stamina, get you in shape, and reduce risk of injury.
1. Hill Top Runs: Sprint up the hill and walk down while you catch your breath. These build muscle naturally, give you a great explosive first step, and are actually easier on the knees as the angle creates support for the joint. Do not run downhill. Repeat, do not run down hill.
2. Run on the beach or sand, lastly grass: do agility movements, short movements of tennis (forehands, backhands, volleys, approaches, serves, returns, and all the shots). This works your legs and body beyond belief. It's shadow movement that gets you ready to be automatic while in the heat of battle. When you practice it, do it properly and with good technique. YouTube provides great models for technique. The harder you push the harder you gain, it's that simple. It doesn't have to take long. 20 Minutes will absolutely kill you.
3. Jump Rope: on a soft as possible surface, preferably clay or dirt.
4. Ride a bike: and sprint for short spurts.
5. Visualize: the feel of shot packages in your mind, using your shot shots in competition against various spins, power, depths and movements on the court. This takes only a few moments per day. You can do this before you practice and then make adjustments to your visualizations after practice and play. When you can bridge your mind, to your body, emotions, and energies you become your truest expression of your highest form on the court. This particular area is something I will be exploring in 2019 and will keep you updated monthly.