The Biomechanics of the Shoulder in Tennis: A Deep Dive
The shoulder joint: When precision meets power
When I think about tennis, I envision the silky, almost effortless precision of Roger Federer as he strikes the ball, his movements exuding grace and control. Yet, beneath this fluid exterior, the forces travelling through his shoulders likely rival those experienced by Rafael Nadal, whose powerful and relentless style of play generates immense physical demands. Despite their contrasting styles, both players rely on their shoulders to deliver exceptional performance under extreme forces.
So, what exactly happens to the shoulder when playing tennis?
The shoulder is a remarkable joint, offering the widest range of motion in the human body—a necessity for the diverse demands of tennis. Whether executing a blistering serve, a slicing volley, or a topspin forehand, the glenohumeral joint takes centre stage. However, as I mentioned in my previous post, the shoulder relies heavily on active stability provided by the rotator cuff muscles and deltoids rather than passive stabilisation through ligaments or joint structure.
This means that the high forces and repetitive movements involved in tennis place significant strain on the shoulder’s active stabilisers, making it vulnerable to overuse injuries, muscle imbalances, and compensatory dysfunctions.
Let’s first examine the shoulder’s extraordinary range of motion to better understand its capabilities and limitations before diving into the biomechanical stresses it endures in tennis.
The glenohumeral joint (GH joint), often referred to as the ball-and-socket joint of the shoulder, offers the greatest range of motion (ROM) of any joint in the human body. This incredible mobility allows for movements in multiple planes:
Internal Rotation and External rotation
The ROM for internal rotation is approximately 81.53 ± 7.03 degrees. However, this range can vary depending on the method of assessment. Research highlights the variability and challenges in standardising these measurements, especially in athletes whose repetitive motion patterns influence shoulder mobility (Manske & Prohaska, 2012; Meister et al., 2012).
External rotation is a key movement for tennis players, particularly during the cocking phase of a serve, where the shoulder reaches its maximum external rotation to generate power. The average range of motion for external rotation is 104.54 ± 11.09 degrees, demonstrating the shoulder’s remarkable capacity to achieve the extreme positions required for optimal performance (Manske & Prohaska, 2012; Meister et al., 2012).
Flexion and Extension
Flexion is essential for overhead movements, including serves and smashes in tennis. The mean range of active shoulder flexion varies slightly by gender.
Males: 159.9° for the left side and 161.5° for the right side.
Females: 157.1° for the left side and 158.5° for the right side.
These findings are based on a study involving over 2,400 participants, which stratified shoulder range of motion by age and gender, revealing natural variability and a slight decline in flexion with age, particularly in females (Gill et al., 2020).
Extension, the backward movement of the arm, is vital for the preparatory phase of strokes and other sports movements. The normal range of active shoulder extension is approximately 50 to 60 degrees, supporting dynamic and stabilising actions during athletic performance.
Abduction and Adduction
The movements of abduction and adduction are integral to the dynamic actions of the shoulder, especially in sports like tennis. These opposing movements—abduction lifting the arm away from the body and adduction bringing it back—work together to create fluid and controlled shoulder mechanics.
Abduction is essential for many tennis-specific actions, including explosive serves, overhead smashes, and topspin shots. The mean range of active shoulder abduction differs slightly by gender:
Males: 149.7° for the left side and 151.5° for the right side.
Females: 147.7° for the left side and 149.7° for the right side.
These findings, derived from the same study mentioned earlier looked at over 2,400 participants, highlight natural variability and the slight advantage in range seen in dominant arms. This motion allows players to elevate their arm effectively, ensuring power and control during high-performance actions (Gill et al., 2020).
Adduction, the motion of bringing the arm back toward the body, is equally important in tennis. This movement helps control the follow-through of strokes, stabilises the arm during volleys, and balances the shoulder after rapid, explosive actions.
While precise normative data on shoulder adduction is less widely reported, typical active adduction ranges between 30–50°, depending on individual variability and shoulder health.
Adduction is critical for the recovery phase of a stroke, allowing the arm to return to its starting position with controlled motion, reducing strain on the shoulder girdle. Together, abduction and adduction form the foundation for the fluid, coordinated shoulder mechanics required in tennis.
Horizontal Abduction, Horizontal Adduction, and Circumduction of the Glenohumeral Joint
In addition to traditional motions like flexion, extension, abduction, and adduction, the GHJ also allows for horizontal abduction, horizontal adduction, and circumduction—movements that underpin the fluidity and power of tennis strokes.
Horizontal Abduction is the movement of the arm away from the body in the horizontal plane. This movement is prominently involved in the wind-up phase of a stroke, such as preparing for a powerful forehand or backhand. It allows players to generate the torque and power needed to drive the ball effectively.
The ROM is Approximately 30–40°.
Horizontal Adduction is the movement of the arm toward the body in the horizontal plane. This motion is critical during the follow-through phase, ensuring smooth transitions and precise control of strokes. Whether completing a serve or finishing a groundstroke, horizontal adduction helps stabilise the shoulder and maintain shot accuracy. The ROM is approximately 90–120°.
Circumduction is a circular motion that combines flexion, extension, abduction, and adduction, creating a full arc of movement. This movement is pivotal for the fluidity of strokes, particularly in overhead serves and smashes. Circumduction allows for seamless transitions between phases of motion, ensuring efficiency and reducing unnecessary strain on the shoulder.
The Kinetic Chain in Tennis
The tennis serve is a dynamic motion broken into five distinct phases:
· Wind-up: Involves knee flexion and trunk rotation to generate initial energy.
· Early Cocking: The shoulder begins to externally rotate, preparing for acceleration.
· Late Cocking: The shoulder reaches maximal abduction and external rotation.
· Acceleration: Force is rapidly transferred through the arm as the ball is struck.
· Follow-Through: The arm decelerates to absorb force and prepare for recovery.
Each segment of the body (legs, hips, trunk, shoulder, elbow, and wrist) contributes to the final energy needed to hit the ball. The kinetic chain ensures that energy flows seamlessly from the ground up, with the leg/hip/trunk link generating over half of the total kinetic energy. The shoulder acts as a funnel and regulator, transferring and refining this energy for effective power delivery through the arm and wrist.
Breakdowns in the kinetic chain, such as weak core or hip function, increase the demand on the shoulder. This can lead to overuse injuries as the distal segments (shoulder, elbow, wrist) attempt to compensate.
Scapular Function
The scapula, or shoulder blade, plays a critical role in ensuring smooth and stable shoulder movement:
· Base for Stability: The scapula provides a stable socket for the humeral head during overhead actions like serving and smashing.
· Mobility for Function: It must move dynamically around the thoracic wall, retracting and protracting during the serve.
· Upward Rotation: Clears the acromion, ensuring unobstructed movement of the humeral head.
Muscle Coordination: Proper scapular motion relies on balanced activation of muscles such as the serratus anterior and trapezius. Dysfunction or weakness in these muscles can lead to scapular dyskinesis, reducing shoulder efficiency and increasing injury risk.
Key Shoulder Actions in Tennis
By managing extraordinary demands due to the high velocity and repetitive nature of the sport. The following outlines the forces, mechanics, and risks associated with tennis-specific movements:
The Serve
Rotational Speed: Elite tennis players generate shoulder rotations exceeding 2,500–3,000 degrees per second, equivalent to seven full circles per second (Watson et al., 2020).
Forces Involved:
· Internal Rotation Torque: Up to 60–80 Nm during the acceleration phase (*to help visualise this, see comparison below).
· Joint Compressive Forces: Up to 1.5–1.8 times body weight at ball impact to maintain joint stability.
· Distraction Forces: Approximately 750 N (76.48 kg) during deceleration, placing strain on the rotator cuff and capsule.
· Capsular Stretching: Extreme external rotation during the late cocking phase stretches the anterior capsule, increasing injury risk.
Forehand and Backhand Strokes
Forehand: Requires horizontal adduction combined with internal rotation, engaging both large muscles like the pectoralis major and smaller stabilisers like the rotator cuff.
Backhand: Combines horizontal abduction with external rotation, demanding balance and precision.
GH Joint Forces:
· During forehand drives, maximal contact forces on the glenohumeral (GH) joint can reach 3,573 ± 1,383 N, approximately 1.25 times greater during the forward swing phase compared to follow-through.
· These forces primarily target the anterior-superior glenoid, generating significant shear stress (Watson et al., 2020).
Overhead Smashes
Mechanics: Involve rapid acceleration and deceleration of the arm.
Risks: Fatigue or poor technique can lead to rotator cuff overuse, impingement syndrome, or scapular dysfunction.
Key Takeaways
The shoulder’s role in tennis is both dynamic and demanding, requiring a balance between mobility, stability, and power. Optimal function depends on an efficient kinetic chain that transfers energy from the legs and core to the shoulder, strong scapular stabilisers to maintain alignment, and balanced muscle strength to prevent imbalances. The repetitive high forces involved in tennis highlight the importance of targeted conditioning, proper technique, and recovery strategies to minimise the risk of injury. By understanding these mechanics, players can enhance performance and protect their shoulders for long-term success on the court.
Coming Up Next: Shoulder Injuries in Tennis
In the next blog, I’ll delve into the common shoulder injuries associated with playing tennis. We’ll explore:
· The most frequently seen conditions, such as rotator cuff tendinitis, impingement syndrome, and labral tears.
· How the biomechanics of tennis strokes and repetitive overhead motions contribute to these injuries.
· Practical strategies for prevention, rehabilitation, and recovery to keep your shoulders strong and injury-free.
Stay tuned for insights into keeping your shoulders in peak condition while playing tennis!
*To put the initial figure into perspective, imagine using a wrench to tighten a bolt: The force required to achieve 60–80 Nm of torque is about the same as applying 6–8 kilograms (13–17 pounds) of force to the end of a 1-metre-long wrench. Alternatively, if the wrench were shorter (say, 0.5 metres long), you’d need to apply 12–16 kilograms (26–35 pounds) of force to generate the same torque. In practical terms, it’s the force you’d exert on a spanner to tighten the lug nuts on a car wheel—quite a bit of effort, especially for the shoulder to generate at such high speeds repeatedly during tennis serves.