Introduction
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Over 18 million people in the United States (US) participate in tennis at least once a year, with an additional 14 million expressing interest in playing tennis.
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Five million people play tennis at least twice a month.
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More than 500,000 adolescents participate in tennis.
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Roughly 650,000 people play in the US at the competitive level.
Epidemiology
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Estimates range from 0.04 to 20 injuries per 1000 hours of tennis played.
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Most injuries occur in the lower extremity (up to 67%), followed by the upper extremity and finally the trunk.
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A majority of injuries are sprains or repetitive trauma overload injuries.
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Acute injuries usually present in the lower extremity, whereas repetitive/chronic injuries tend to occur in the upper extremity and trunk.
General Principles
Physiology
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Intermittent high-intensity exercise that requires aerobic and anaerobic fitness
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Tennis is a noncyclical anaerobic sport (10%–30%) with an aerobic recovery phase (70%–90%).
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Single rallies may only last 3–8 seconds, but complete matches may last for up to 3 hours.
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Over the course of a match, 300–500 bursts of effort may be expended.
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Tennis requires elements of quickness, endurance, strength, flexibility, reaction time/speed, agility, and coordination.
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Movements include sprinting, twisting, side-to-side running, sliding, jumping, lunging, and quick stops.
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On an average, the heart rate in singles tennis can be >160 beats per minute, >80% of the average maximal heart rate.
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Depending upon conditioning, age, gender, play intensity, hydration status, and environment, a player may lose 0.5–2.5 L of water per hour of play.
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Conditioning includes both aerobic and anaerobic fitness as well as progressive resistance strengthening of key muscle groups, including strengthening of the core and scapular stabilizers.
Equipment/Facilities
Racquet composition: Change in manufacturing materials has resulted in racquets that are larger, lighter, stiffer, and more powerful than racquets of the past. Increased head size and increased stiffness may reduce arm vibration; however, to date, no studies have determined its effect on injury or provided any evidence on optimal racquet selection for injury prevention.
Court surfaces: Play a role in the types of injuries seen
Clay surface: Loose surface causes the ball to rapidly lose speed and bounce higher; allows increased time for the opponent to reach/return the ball; considered a “slow” surface; this allows for longer rallies and matches, resulting in overuse injuries. The forgiving surface is gentler on lower extremity joints, and certain studies have suggested that the risk of injury is lowest on clay courts. However, due to the loss of speed of the ball, the power to hit the ball hard must come from the kinetic chain, resulting in upper body and back overuse injuries as well. Further research is needed to establish whether playing tennis on clay courts results in fewer injuries, particularly in the lower extremity and trunk.
Hard surface: Concrete, coated asphalt; balls bounce low, giving hard-hitting players an advantage; considered a “fast” surface; harder impact to the lower extremities, with stress fractures of the lower extremities and other injuries, such as patellofemoral pain, more prevalent; sudden stops and starts make tennis toe and ankle sprains more common on this surface. Because a powerful serve is more important on this surface, injuries due to serving are more common.
Grass surface: Grass grown on hard, packed soil; balls tend to slide and bounce low, making returns difficult; favors the serve-and-volley player; considered the “fastest” surface; however, unevenness of the surface may result in slipping and sprains in the lower extremity.
Indoor courts: Allow for year-round play; usually have a hard court surface
Mechanics of Tennis
Kinetic Chain
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The kinetic chain is the efficient transference of force from the ground to the racquet through the coordinated sequencing of the legs, hips, trunk, and upper extremity.
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Each segment transfers more energy than the previous one, resulting in maximal racquet acceleration.
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Fluid motion through the kinetic chain is essential to generate a powerful swing and minimize the risk of injury.
Strokes
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75% of play involves the forehand and serve.
The Serve
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Considered the most important stroke of the game and is also the most commonly associated with injury
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The service motion puts a significant stress on the lower extremities, spine, abdomen, and shoulder, although certain phases of the serve are more apt to cause injury than others.
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Four phases: wind-up, cocking, acceleration, and follow-through ( Fig. 76.1 )
Figure 76.1
Phases of serve.
Four Phases of Serve
Wind-up: From the standstill (ready) position, this phase is the initiation of the serving motion and ends with the toss of the ball by the contralateral extremity (when the ball leaves the hand). The lower extremities prepare for the build-up of power that occurs in the cocking phase as the knees and hips bend. The hips and back rotate toward the dominant extremity (see Fig. 76.1 ).
Cocking: From the release of the ball for the toss, through the point where body motion stops moving backwards, toward the dominant extremity side; the arm holding the racquet appears to be in maximal external rotation (see Fig. 76.1 ) and is abducted 90°–100°. This phase is characterized by the building up of power. Energy is stored by prestretching of the muscles. Subject to injury:
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The anterior shoulder capsule is tensioned to its physiologic limit with the shoulder in maximum external rotation.
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The glenoid labrum helps prevent shoulder subluxation during external rotation and translation.
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With abduction, horizontal abduction, and external rotation of the humerus, internal impingement may occur.
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Muscles of the lower extremity during extension from a flexed (loaded) position
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Intervertebral disc, pars interarticularis with hyperextension/rotation of the spine
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Wrist extensors
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Acceleration: This phase is characterized by the body moving forward and upward as the dominant shoulder appears to be in even greater (maximal) external rotation initially and internally rotates to ball impact. High muscular activity is noted with peak activity before ball impact (see Fig. 76.1 ) as energy in transferred along the kinetic chain. Internal rotation of the humerus is responsible for 40% of the racquet speed at impact. Fluid motion through the kinetic chain is crucial. Injury to one segment will lead to a loss of power and place another segment at a risk of injury. 54% of the energy used in the tennis serve comes from the lower extremity and trunk. Subject to injury:
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Muscular overload of the rectus abdominus, obliques, hip adductors and rotators, rotator cuff, glenohumeral internal rotators and adductors, elbow extensors, and wrist flexors may occur.
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Superior labrum with extreme abduction and internal rotation of the humerus
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Ulnar lateral collateral ligament (LCL) and the flexor–pronator muscles of the elbow secondary to valgus stress
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Extensor carpi ulnaris tendon at the wrist with hypersupinated and ulnarly deviated wrist (for topspin/slice)
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Follow-through: Ball impact through completion of the stroke; activation of shoulder musculature is required to decelerate the humerus to maintain glenohumeral stability. Long-axis rotation through the arm via internal rotation of the shoulder and forearm pronation helps in the dissipation of forces. Subject to injury:
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The posterior shoulder muscles contract eccentrically to slow the internal rotation of the shoulder.
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The rotator cuff acts to maintain the humeral head within the glenoid.
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The biceps function to slow forearm pronation and elbow extension and assist in stabilizing the glenohumeral joint.
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The posterior capsule is placed under tension as it counters distraction forces.
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Scapular motion combined with contraction of the infraspinatus muscle places the suprascapular nerve, located in the spinoglenoid notch, at a risk of injury.
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Kinematics
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Racquet speeds reach a peak velocity of 62–83 minutes/hour.
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Ball velocities reach 83–153 minutes/hour.
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The aforementioned speeds are achieved in 0.2–0.3 seconds from the end of the cocking phase until ball contact.
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Shoulder rotates internally at 1100°–1700°/second.
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Elbow flexes to 120° during late cocking and extends to 15°–20° of flexion at ball impact, resulting in an extension velocity of 900°–1000°/second.
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Forearm pronation has been recorded at 350°–900°/second before ball impact and has been documented to increase to 1300°/second, 0.1 seconds after impact.
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Wrist speeds approach 1000°/second, 0.1 seconds before ball impact, ROM of wrist during a serve is 90°–100°.
Ground Strokes
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Forehand and backhand
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Each has three phases: preparation, acceleration, and follow-through
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Each may be hit open stance (feet aligned parallel to the net/baseline) or closed stance (feet aligned perpendicular to the net/baseline).
Backhand
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The backhand groundstroke may be performed one- or two-handed. The one-handed backhand stroke allows the player to have a better reach and the ability to slice the ball more effectively. The two-handed backhand stroke requires less arm strength but requires more trunk rotation and may result in greater power and accuracy and is considered easier to learn with fewer moving segments to control.
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There is an increased incidence of lateral elbow pain in novice players in the backhand stroke, particularly the one-handed backhand. This is attributed to not using the trunk and shoulder musculature appropriately, placing more stress across the elbow joint, and from hitting the ball with the wrist in flexion (versus neutral or extension). Players should strive to hit the ball in front of their body to reduce injury to the elbow.
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Using a two-handed backhand reduces the risk of elbow injury owing to a greater need for trunk rotation to hit the backhand while maintaining appropriate elbow and wrist position.
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Wrist pain is also common with the two-handed backhand stroke as players “flick” the racquet at ball contact. Appropriate technique, taping of the wrists, and strengthening exercises will reduce injury to the wrist during this stroke. In particular, the nondominant wrist is more often injured in players who use a two-handed backhand in the preparation phase as the wrist is in an extended, ulnarly deviated, and supinated position.
Forehand
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Players may hit the forehand shot with a Western, semi-Western, or Eastern grip.
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The Western and semi-Western grip allows greater production of topspin and is more suitable for play on clay or slow, hard courts. However, this style places more of a valgus stress on the elbow.
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The Eastern grip allows the player to slice the ball and is utilized on grass or carpet surfaces by serve- and volley-type players.
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The forehand shot has three phases: preparation, acceleration, and follow-through.
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