The Tennis Player's Serve and the Biomechanics of Power
A 17-year-old tennis player has a first-serve speed of 165 km/h but only a 48% first-serve percentage in matches. Video analysis shows that she bends her knees only slightly, rotates her trunk early, and snaps her elbow rather than using a full leg drive and trunk rotation. Her toss is low and slightly behind her. She also reports right shoulder pain that appears only during serving and worsens through a match. Her coach wants to increase her serve speed to 180 km/h by adding more upper-body effort.
1. Analyse the serve using biomechanical principles and explain why adding more upper-body effort is unlikely to achieve the coach's goal.
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The serve is a kinetic chain action: force is generated from the ground up, transferred through the legs, hips, trunk, shoulder, elbow, and wrist, and finally to the racket. Efficient technique uses the large, strong segments first and allows the smaller distal segments to accelerate the racket head.
In this player, the kinetic chain is incomplete. Limited knee bend reduces the ground reaction force and the contribution of the legs and hips. Early trunk rotation means the trunk rotates before the legs have driven, so the sequencing is out of order and energy is not transferred efficiently. Elbow snapping rather than a coordinated shoulder and forearm action concentrates load on the elbow and shoulder.
The low, slightly behind toss reduces the ability to reach a high contact point and to use the legs to drive upward and forward. A higher contact point gives a better angle and more time to accelerate the racket.
Adding more upper-body effort would increase load on the shoulder and elbow without addressing the missing contributions from the legs and trunk. It would likely reduce accuracy further and increase shoulder pain. To reach 180 km/h, the player should improve sequencing and the contribution of the lower body and trunk, which will increase racket head speed without overloading the shoulder.
2. Explain the likely cause of the shoulder pain and outline technique and conditioning changes that would reduce the risk of injury while improving performance.
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The shoulder pain during serving is most likely related to overload of the shoulder structures during the acceleration and follow-through phases, combined with poor sequencing. When the legs and trunk contribute little, the shoulder must generate more force and rotate faster, increasing the load on the rotator cuff and surrounding tissues. The elbow snap also adds stress. Pain that worsens through a match suggests cumulative overload rather than a single acute event.
Technique changes:
- Increase knee bend and leg drive so the ground reaction force contributes to racket head speed.
- Sequence the trunk after the leg drive, using hip and trunk rotation to transfer force.
- Toss the ball higher and slightly more forward so contact is at a higher point and the player can drive up and through the ball.
- Replace the elbow snap with a coordinated shoulder and forearm action and a full follow-through.
Conditioning changes:
- Strengthen the rotator cuff and scapular stabilisers with controlled exercises.
- Develop trunk and hip strength and power, and leg strength, so the larger segments can contribute.
- Include mobility work for the shoulder and thoracic spine.
- Manage serving volume in training and monitor pain; reduce serving load if pain increases.
These changes should be introduced gradually and reviewed with a coach and, for the shoulder pain, a physiotherapist. Improving sequencing should increase speed while reducing the load on the shoulder.