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Ask the High Performance Lab - Oct. 5

May 25, 2008 12:25 PM

PLEASE NOTE: The medical opinions in USTA.com's Ask the High Performance Lab are responses intended for the average player. Please consult with your primary physician before beginning any new exercise program.

Dr. Duane Knudson, an expert of tennis biomechanics, serves on the USTA Sport Science Committee.
Dr. Duane Knudson is internationally known as an expert on the biomechanics of tennis and has served several terms on the United States Tennis Association Sport Science Committee. He is Associate Dean of the College of Communication and Education and a Professor in the Department of Kinesiology at the California State University, Chico. His primary areas of research are the biomechanics of tennis, stretching, and the qualitative analysis of movement.


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).

Q: Your feature on functional lunges was great, but because of prior meniscus surgery I've been told by my orthopedist not to do a) lunges or b) leg extensions. What other exercises can I do that would achieve the same or similar lower leg strength and body balance. By the way, I am a 61 year-old male playing at a 4.5 level.

A: I would not try any new exercises before clearing them with your surgeon. He/she is the one who has seen the inside of your joints and knows the most about your particular situation. I would recommend that you ask him/her if you could half—squats, leg presses with low weight, and climb stairs as substitute exercises.

Q: I would like to know a safe exercise for the legs that will not hurt the knees but will strengthen the legs. I have problems getting fatigued legs in a long match from the knee bends used when serving.

A: Most traditional exercises for the legs are safe for the joints of the leg if done with correct technique. The most common leg strengthening exercises are squats, leg presses, lunges, knee extensions. See a certified strength coach for more specific exercise programming. The premier professional organizations in exercise science that have independent, rigorous certification arms are the American College of Sports Medicine (www.acsm.org) and the National Strength and Conditioning Association (www.nsca-lift.org).

Q: I'm curious about common hip injuries associated with hitting an open stance forehand or backhand. Or actually, what I am really interested in is hip injuries due to poor technique on ground strokes (such as opening up too soon, pulling off a shot). Also, what can adult players do to counter this as far as conditioning goes (since it might take awhile to get the form right!).

A: Unfortunately, most tennis injuries are multifaceted so there are few easy answers to injury questions. There are no studies that statistically link open stance tennis strokes with higher rates of certain injuries at the hip joint. Most tennis players could benefit from strengthening hip musculature in all directions (flexion/extension and abduction/adduction). Most players should also stretch the muscles around the hip in all directions too. One recent study of tennis professionals found an association between flexibility losses of hip internal rotation of the lead leg and lower back flexibility.

Q: What treatment is recommended for painful or tight hip flexors post match, and what should players do to prevent injury/stress to the hip flexors? When should players return to match play or practice?

A: Hip flexors are muscles on the front of your hip and thigh that help you quickly swing the leg forward as you run about the court. For most players strength is not the issue but flexibility. If your knee is strong a good stretch is to bend your knee and grab your foot behind you and gently pull your leg backward. More advanced stretches are splits (rear leg) or elevating your leg behind you and placing the top of your foot on a short bench/fence.

One of the hip flexors (rectus femoris) crosses both the hip and knee joints, so combinations of hip extension with and without knee extension will allow you to focus stretching on this superficial muscle or the deeper hip flexors in the pelvis/lower back. To reduce the risk of painful hip flexors one should both strengthen these muscles away from the court and stretch them to maintain their flexibility.

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