It is all a Matter of Balance
Russell Gunner, C.A.T. (C)

Unless you are a "switch hitter", you play tennis with the racquet in your dominant hand. Tennis like many sports such as squash, baseball, and golf can lead to some level of muscle imbalance in the upper body if the sport is the only thing that the athlete participates in.

Muscle balance is very important for posture, injury prevention, and enhancement of performance.
The racquet side of the body develops very strong but often tight mid back, shoulder, and lower arm muscles. This group of muscles must be stretched more often as they are used more repetitively.

The 'non racquet side' of the body tends to be weaker and needs to be built up more with an off season and in season weight program(or body weight conditioning program for the younger athletes). In tennis there is also evidence in the literature of development of imbalances between opposing muscles. For example, elite tennis players studied have been found to have significantly decreased range of motion of the internal rotators compared to the external rotators of the shoulder.

Having balanced strength and flexibility will lead to improved reaction time and power in both directions.

In general, all stretches should be done after a light warm-up such as a light jog or cycle for approximately 5-10 minutes. Each stretch should be held for approximately 15-30 seconds and repeated 2-3 times.