Internal Shoulder Rotation:
Key to Serving Power

Chas Stumpfel

Follow John Isner's elbow as you look for the upper arm to rotate as it adds speed to the racket. This is internal shoulder rotation.

After playing tennis for over 40 years, I made a sudden and unexpected discovery about the serve. In the 1980s, I had played league tennis at the 3.5 to 4.0 level and for two years had won the championship of a larger league at work.

I played serve and volley tennis and my serve was very effective at my level. I had worked frequently and seriously on improving my serve. But it never progressed to a higher level of pace. I read every tennis book available, but there were no new ideas and I basically gave up the idea of improving my serve further.

Then in 2011, I learned about research that showed the primary source of racket speed in the serve was created by something called "internal shoulder rotation". According to the Australian biomechanical researcher Bruce Elliott, internal shoulder rotation was responsible for 40% of forward racket head speed.

Internal shoulder rotation, the research also showed, was set up by something else called "external shoulder rotation." I had never heard these terms.

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Chas Stumpfel is a research physicist (retired) with a background that includes various high speed imaging applications. He is a recreational player who has been interested in tennis stroke techniques since the 1970s, especially those for the serve. In 2011, he was surprised and fascinated to learn of research of that showed the racket head speed for the serve was largely powered by a joint motion that was not well known in tennis.

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