We are in a day and age when everyone thinks that cardio refers to a 3 mile run or a 30 minute jog. Long distance jogs are what cardio is. Too many athletes are in that mind set and feel that their best training will come with a long endurance run.
As a strength coach I don't believe that is the way for a tennis player to train. Why? How often is a tennis player jogging 3 miles in a match? Never. The athletes time could be much better spent performing sprints, intervals or conditioning circuits. Tennis is a game of quick, explosive movements and requires the use of all different energy systems so it's important to train the body in that manner. Rather then a long steady jog why not sprint for 30 seconds and jog for 1 minute, or sprint for a distance and jog for a distance. Add some change of pace in your run with some short explosive sprints followed by active recovery.
If running isn't your thing (if you're a tennis player you WILL need to do short sprints) then try substituting it with a conditioning circuit. This kind of circuit can be made however you want it. You can perform a circuit of bodyweight exercises (squats, push ups, jumping jacks, etc...) or weights (Dumbbells, barbells, kettle bells, etc...). This will incorporate strength exercises with minimal rest to create a more metabolic type of training to work on endurance and muscular endurance.
One thing these endurance runs are good for however is establishing a base of conditioning. It's a good start especially for someone who hasn't done a lot of fitness. A nice long distance run is an easy way to build up a foundation to start training from. It's also a good thing to incorporate in your workout occasionally but not all the time. You can get a much bigger bang for your buck with other methods of conditioning.
Example Body Weight Conditioning Circuit:
Perform each exercise for 20sec, no rest between exercises. Perform 3-5 sets
- Squat Jumps, Push Ups, Squats, Jumping Jacks, Lunges, Inch Worms
Example of Dumbbell Conditioning Circuit:
Keep the weight light to work on speed and technique, perform 3-5 sets, make sure to have a partner to spot and assist
- Squat to Press x10, Dumbbell Rows x10, Walking Lunges x10, Dumbbell Chest Press x10, Bicep Curls x10