Technique & form
If you use the correct technique, you achieve power correctly rather than through counter productive and excessive body movements and torque. An incorrect swing in tennis, often indicates that the person is relying only on the arm to hit the ball, rather than transfer of body weight and uncoiling the trunk correctly.
Failure to warm up and cool down
Warming up and cooling down is extremely important to reduce the risk of muscle and joint injuries. Warming up will not only help avoid injury but will also improve performance.
Repetitive stressful motion on a leg or arm can over time create a painful stress fracture. In a leg, this can include a spiral fracture where the crack in the bone resembles a spiral staircase. These can be difficult injuries to recover from.
Your body needs recovery time between events. This is common problem with Spring training in baseball, where teen athletes throw for three hours straight in practice sessions, only to tear a rotator cuff, or create a ligament strain in the elbow.
Refrain from any activity that causes shoulder pain. Give it a rest and find an alternate activity or exercise that does not cause the pain.
Many times people never fully give themselves time to recover from an earlier strain or sprain, and this can lead to similar strain in the future.
Keep your shoulders slightly back and your head up to prevent shoulder pain. When your shoulders slump forward this can lead to increased pain in the joints.
Prevent shoulder pain when working at a desk or computer by positioning your keyboard and mouse so that your arms can be relaxed at your side. There should be a slightly open angle at the elbow and the wrists should be straight.
If you work at a computer during the day, taking short breaks every half hour can help rest your neck and shoulders. For example, you can cross your arms and place them on your desk. Then rest your forehead on your arms to allow your shoulders to relax.