Q. I have heard the kick serve can be very hard on the shoulder. Two questions: At what age is it safe for a female athlete to begin work on that type serve and what rotator cuff exercises are best to prevent injury for that type serve?
A. The kick serve is often compared to throwing a curve ball in baseball, in terms of the stress that is placed on the shoulder.
There is so much concern about protecting the shoulder in little league baseball, in fact, that there are rules in place in many leagues that makes it "illegal" to throw curveballs until the player has reached a certain age - the penalty for throwing a curve ball getting thrown out of the game. In tennis there are no such rules but the general recommendations are not to start hitting the kick serve until the player has reached puberty.
A player can learn the mechanics of the serve prior to puberty, but should not practice it extensively or use it in competition. Adopting this strategy will help the player develop the technique but will also protect the shoulder from injury and "delay" the stress placed on the shoulder until the player has sufficient strength to handle the loads.
With that said, there are also strengthening exercises that every player should do to protect the health of the shoulder. These exercises include strengthening of the muscles that externally rotate the shoulder (the motion opposite of what a player does when hitting a serve) and control the shoulder blades in the upper back. Both groups of muscles are important for developing shoulder strength and stability.
Q. My 10 year old son has been working on a kick serve with his coach for the last 6 months and can hit it quite well. Recently, someone watching him play in a tournament expressed concern to me that this serve is akin to a curve ball and was dangerous for him to hit. Should a 10 year old boy be hitting a kick serve or can it cause an elbow or shoulder injury because he is not physically mature?
A. This is a good question and the answer depends on many factors like physiological age of your son, the pattern of serving and rest he normally undergoes, and what you mean by “dangerous.” American baseball organizations have been very aggressive in establishing rules for pitch counts and recommendations for certain pitches by age. The science has only documented the motions and forces of the various pitches, and not established an association between different pitches and injury rates.
A pitcher make the final pushes off the top of the ball in a curveball by delaying forearm rotation and using more wrist motion sideward (toward the little finger). The tennis player can hit up through the rear side of the ball from leg extension to get topspin so it is possible that there is less stress on the wrist. If your son has good coaching to use correct technique, is not physically less mature than most body, and does not hit too many serves without adequate rest days he should be fine.
If you want to play it safe the baseball researchers do not usually recommend pitching curveballs before the ages of 13 or 14 (Sports Medicine Update 1999 14(3): 11-15).