The tennis serve provides strength and conditioning specialists, sport scientists, players, coaches, physical therapists, and athletic trainers a great opportunity to improve performance. It can also lead to potential injury if the stroke is not performed with appropriate technique or if the physical aspects of the athlete (strength, speed, power, flexibility, muscular endurance, and muscular balance) are not trained correctly. It is the only stroke in tennis that is 100% under control of the player, and it is not a response to a ball hit by an opponent. The serve does produce large loads on the shoulder and lower back, which can result in overuse injuries (4,12,18,20). It is also a highly complex stroke because of the reliance on multiple segments in the kinetic chain to produce power through properly timed rotations and complex coordinated muscular activations (28), as well as the most important from a strategic standpoint (15,19). The difficulty in the movement results from the summation of forces from the ground up through the kinetic chain and out into the ball. This summation of forces is also required in forehand and backhand groundstrokes for successful stroke performance. On the serve, if this is successfully performed, this summation of forces is achieved while also throwing the ball upward (with the nondominant hand) and impacting the ball just below its peak on its downward flight (2). Effective servers use the kinetic chain via a muscle activation synchrony of the coordinated lower extremity muscles that provide a stable base for the trunk/core to rotate and extend and flex while also helping to produce force. If any of the links in the chain are not synchronized effectively, the outcome of the serve will not be optimal (i.e., velocity, spin, placement, and reliability) (17).
The serve has been studied in a similar manner to the baseball throwing motion, and although much can be gained from the data in baseball, some vital differences exist between the serving motion and the throwing motion (5,14). Some of these differences include the planes of motion, the use of the nondominant arm, the trajectory of the forces produced and released, technical components of the movement of the lower body and hips, as well as the variety in ball placements. Another major difference is that unlike in baseball pitching, the tennis serve has a long segment (tennis racket) that hits the ball, as opposed to a shorter lever (in baseball) that throws the ball (5,12,14).
The purpose of this article is to provide a practical performance evaluation of the tennis serve using 8 specific stages, and from these 8 stages, tennis-specific exercises can be incorporated based on areas of identified weakness or to improve performance. This article will build upon the small body of literature on serve-specific strength and conditioning exercises that can improve the performance and reduce injuries associated with the tennis serve (19,25,26). To fully evaluate the tennis serve, a need exists to alter the components usually seen in the traditional throwing analysis (13,16). The 6 stages of the traditional throwing analysis are (a) windup, (b) early cocking/stride, (c) late cocking, (d) acceleration, (e) deceleration, and (f) follow-through, whereas the following 8-stage model is a more detailed analysis tool for strength and conditioning specialists and coaches. The 8-stage model has 3 distinct phases— preparation, acceleration, and follow-through phases. The phases describe 3 distinct dynamic purposes of the tennis serve: to store energy (preparation phase), to release energy (acceleration phase), to decelerate and come to a complete stop (follow-through phase) and prepare for the next movement. However, before specifically discussing each of the stages, a brief discussion of the kinetic chain's role in the serve is needed. To highlight the role of the entire body in these stages (Figure 1), a segmented analysis is very helpful from a clinical understanding. Each stage is a direct result of muscle activation and technical adjustments made in the previous stage, and it is important when evaluating an athlete to look at the serve from a total body perspective and not only in a segmented fashion. These 8 stages are listed as specific time points. Remember that movements occur between each still photograph, which represent the true dynamic characteristics that occur during each stage of the tennis serve. It also needs to be highlighted that 2 stages are actually a specific split-second point in time (cocking and contact), and although described as a stage for language consistency purposes in the analysis, they actually represent a mere instant in time.
PHASES AND STAGES OF THE TENNIS SERVE
PREPARATION PHASE—START STAGE (STAGE 1)
The start of a player's serve is a rather individual aspect of the service motion and does not directly influence the force production due to no ground reaction forces (GRFs) above those of standing at this point in the motion (Figure 2) (27). Many players start using varying technique, feet positions, and timing. The goal of the start is to align the body to best use GRFs throughout the remainder of the service motion. Most individual differences seen during the start stage of the serve are stylistic and do not necessarily have any direct influence on the outcomes of the serve (speed, spin, accuracy, and consistency). However, general training for balance and stability is helpful during this stage.
Exercise: balance disc tennis service-specific isometric quarter squat
Stand with a balance disc or stability trainer under each foot assuming the starting position of the service motion. Maintain optimal balanced position with slight knee bend and hands together in front. Hold for a period of 30 seconds and repeat several times. Be sure to use a racket and ball to best simulate the balance position of the serve motion (figure 3). An additional variation of this exercise is to do a single-leg balance, which is more difficult to further challenge the body and train to increase proprioception and balance.
PREPARATION PHASE—RELEASE STAGE (STAGE 2)
This stage is the time when the ball is released from the nondominant hand (left hand in a right-handed server), and this is a very important stage of the entire service motion because the ball release and positioning of the ball in air is vital in determining the ball contact; also it is important that this release stage is performed correctly (Figure 4). Unfortunately, no valid and reliable published data have been performed on the outcomes of how different release angles, heights, spins, and speeds may ultimately influence the remainder of the service motion, specifically the influence on force production, loading mechanics, etc.
Exercise: foam roll—lat
Lay directly on your left side (right-handed server) over a foam roll placed perpendicular to your body as pictured. With the foam roll placed under your side and with the tossing arm in an overhead position, roll back and forth over the foam roll to stretch the latissimus dorsi muscle on your left side. Note that the weight of the lower body is supported on the outside border of the foot. Repeat for several sets of 30-second stretches (Figure 5).
PREPARATION PHASE—LOADING STAGE (STAGE 3)
During the loading phase (Figure 6), there are 2 broad types of lower-body loading (foot position) options—the foot-back or the foot-up technique (Figures 7, 8).
Elliott and Wood (11) showed that players using a foot-up technique developed greater vertical forces, which allowed the players to reach a greater height than players using the foot-back technique. The foot-up technique allows the players to develop greater vertical forces and vertical displacement than with the foot-back technique (3,11). The back leg provides most of the upward and forward push, whereas the front leg provides a stable post to allow a stable axis of rotation. Elliott and Wood (11) have shown that ball velocities were not different between foot-up and foot-back techniques.
Service velocity is correlated with greater muscle forces created by a forceful leg drive during the loading stage (Figure 6) (1). According to 1 study (15), the pushing action, using a backward to forward sequence, as evidenced by the higher horizontal forces in elite-level servers, may be of greatest importance in generating high-speed serves. Therefore, maximizing the leg motion (change in vertical and horizontal forces) will help produce a consistent leg drive that can enhance shoulder action and efficiency. It was found that elite servers, compared with beginner servers, had a greater vertical and horizontal force production. Elite-level servers activate the major muscles of the lower body earlier than less advanced players. This is something that should be emphasized during strength and conditioning training sessions.
In general, the lower trunk (core) muscles become active toward the end of the preparation phase (stage 3, loading; stage 4, cocking) (4). Shoulder and pelvis lateral rear tilt is a component of all powerful servers before the cocking phase (i.e., during the loading phase) (24). The shoulder and pelvis “lateral rear tilt” is shown in Figures 7 and 8 and they describe the movement that places the right shoulder and right hip (in the right-handed server) in a position that is lower than the left shoulder and hip. This rear lateral tilted alignment facilitates the development of angular momentum through lateral trunk flexion during the forward swing, which is a major factor in a high-velocity serve (2).
A front knee flexion angle greater than 15° during this loading stage has been suggested as a good observable marker for effective front “leg drive” (7). The activation patterns of the lower trunk muscles clearly demonstrate a high degree of cocontraction during a tennis serve, especially during stages 3 to 7 (4).
Exercise: high-cable, single-arm, rotational service pull
In a standing position under an overhead cable or piece of elastic tubing, position yourself in the stance position of your service motion. Reaching up to grasp the cable or tubing with your right hand overhead, laterally flex against the resistance, performing the movement of right lateral flexion (right-handed server) and simultaneously pulling the dominant arm downward as pictured. Bend the knees to assume the loading position of the serve. Slowly release the weight or tubing working eccentrically as you fight the resistance back upward to the start position (Figure 9).
Exercise: tennis serve loading stretch
Stand approximately 1 ft from a wall with a strap attached overhead as shown. With your racket arm grasping the end of the strap, assume your serving position (load position) leading forward with your front hip. Hold this position for 30 seconds to gain flexibility in the tensor fascia latae/iliotibial band and quadratus lumborum. Note the position of the knees in a flexed position to simulate loading in preparation for the explosive acceleration movement of the tennis serve (Figure 10). It is important to understand that this stretches the muscles on the nondominant (tossing arm) side because the muscles on the dominant side are actually shortened during this position.
PREPARATION PHASE—COCKING STAGE (STAGE 4)
An effective cocking position (Figure 11) is a result of an efficient loading stage (Figure 6), which aids in increasing the efficiency of the dominant arm in driving the racket down and behind the torso that lengthens the trajectory of the racket to the ball (9), allowing for a greater stored potential energy. High eccentric loads (prestretching) are applied on the internal rotator muscles during the late portion of preparation phase (backswing), which transitions into the acceleration phase (stage 5) before impact (1,21).
Maximum shoulder external rotation was achieved 0.09 (±0.01) seconds before contact in professional tennis players (12). Leg drive was near completion (completion = knee flexion 0°) at this stage (12). At the instant of maximum external rotation, the shoulder was abducted 101° (±13°), horizontally adducted 7° (± 13°), and externally rotated 172° (±12°), the elbow was flexed 104° (±12°), and the wrist was extended 66° (±19°) in world-class tennis players (12). This resulted in a near parallel position between the racket and the trunk (Figure 11). The magnitude of shoulder external rotation is similar to that for elite baseball pitchers (175-185°) (5,14). These large magnitudes of external rotation are actually a combination of glenohumeral rotation, scapulothoracic motion, and trunk extension (5,30). Very high activation levels of the left internal oblique (in a right-handed athlete) are seen in the end of the preparation phase (cocking stage, Figure 11) and during the acceleration phase (4).
The stabilizing and approximating role of the rotator cuff is clearly evident by the high levels of activation during this phase of the tennis serve. The moderately high activity (maximum voluntary isometric contraction 25-53%) (28) during this phase shows the importance of both anterior and posterior rotator cuff strength and scapular stabilization for proper execution of the required mechanics for the cocking stage.
The kinematic summary of the glenohumeral position during the cocking stage is of critical importance in injury prevention in addition to allowing optimal performance during the tennis serve. Studies by Elliott et al. (10) and Fleisig et al (12) both show abduction of 83° and 101°, respectively, in the position of maximal external rotation in the cocking phase. This position also has significant ramifications for injury prevention because of the risk of impingement in the shoulder with excessive arm elevation (31).
Exercise: 2-arm 90°/90° externalrotation
Stand facing the attachment point of the elastic tubing secured at approximately waist height. Keeping the elbows bent 90° and elbows just slightly in front of the shoulders (scapular plane), move the shoulders into external rotation. Start with a position with the forearms nearly horizontal and end with the forearms in a vertical position. Use a controlled movement, especially as you return from the vertical position to the start position (eccentric external rotation muscular contraction) to work the rotator cuff in a lengthening contraction (Figure 12).
Exercise: reverse 90°/90° catch and throw
Assume a half kneeling position (right knee bent for right-handed player) with your shoulder abducted 90° and elbow bent 90° as well. Look slightly behind you toward a partner who is standing approximately 3 to 4 ft back. Have your partner using an underhand tossing motion throw a 0.5-kg-weighted to 1-kg-weighted ball just in front of your hand. Keeping your elbow up, catch the ball and decelerate the movement immediately after catching the ball. Then explosively throw the ball back to your partner and repeat. Be sure to maintain the 90°/90° position during the exercise (Figure 13). Note that with younger junior players, a softball can be used initially because it is lighter and allows for skill acquisition and does not overload the often underdeveloped musculature in this area. Use of a lighter load on this exercise also ensures that explosive movements can be used.
ACCELERATION PHASE—ACCELERATION STAGE (STAGE 5)
It has been shown that elite servers have a quicker acceleration phase (stages 5-6) than beginner servers (15). It is also known that advanced serves move from maximum external rotation to ball contact in less than 0.01 of a second (12). Peak electromyography (EMG) data from the vastus lateralis, vastus medialis, and gastrocnemius occur near the end of stage 5 (Figure 8) (15). All the muscles of the trunk showed their highest EMG values during the acceleration phase of the serve (Figure 14) (4).
Acceleration of the racket before ball impact is accompanied by a rapid reversal of the rotation of the lumbar spine—from hyperextension and right twist or rotation (“counterrotation”) to flexion and left twist (rotation) for a right-hander. This motion (sometimes described as corkscrew) transfers the force of its torque to the spinal segments (8), and it is important that each tennis athlete has a structured core/lower back injury prevention program in place to offset these rather unusual body movements.
Consistent with EMG recordings during the acceleration phase of throwing (13), high muscular activity is present during the forceful concentric internal rotation of the humerus (28). EMG research published by Van Gheluwe and Hebbelinck (29) using intermediate tennis players and by Miyashita et al. (23) using skilled and unskilled tennis players also found high activity levels of the pectoralis major, as well as the deltoid, trapezius, and triceps, during the acceleration phase. Both the reports showed a relative silence of electrical activity in the accelerating musculature during impact, with peak levels of muscular activity occurring just before impact. One exception is the stabilizing contribution of the infraspinatus, which remained active during impact (29). It is important to note the continuous contraction of the rotator cuff in the shoulder during the serving motion both as a stabilizer and as an accelerator in stage 4 (cocking) and stage 5 (acceleration) and the eccentric stabilizing function during the follow-through, but the infraspinatus is most active during contact.
Exercise: plyometric 90°/90° internal rotation in service position
Assume a standing position facing a wall in a service position. At 90° shoulder abduction and 90° external rotation, throw a 1- to 2-kg small medicine ball against the wall, maintaining a stable shoulder position at this 90°/90° position, and catch the ball and repeat the movement (Figure 15).
Exercise: high retraction in 90°/90° external rotation
Stand facing the attachment point of the elastic tubing secured at approximately waist height. Abduct the shoulders 90° in the scapular plane (40° forward from the position directly to your side) to start. Keeping your elbows bent 90° as pictured, move your arms backward squeezing the shoulder blades together. Hold the end range position for one count and return to the starting position. Be careful not to bring the elbows further back, then directly to your side as pictured and remember to focus on the retraction (squeezing together) of the shoulder blades (Figure 16).
ACCELERATION PHASE—CONTACT STAGE (STAGE 6)
At contact (Figure 17), in professional Olympic tennis players, the trunk has an average tilt of approximately 48° above horizontal, the arm (shoulder) is abducted 101°, and the elbow, wrist, and lead knee were slightly flexed (12). These positions are shown in Figure 17. The mean shoulder abduction just before contact is approximately 100°, which supports the 100 ± 10° proposed by Matsuo et al. (22) to produce maximal ball velocity and minimal shoulder joint loading in baseball pitching. In another study (24), the angle of elevation between the upper arm and thorax at impact was approximately 110° in high-performance servers, irrespective of foot-up or foot-back serving technique. This suggests that there is an optimum contact point 110 ± 15° for the tennis serve. It has been shown that elite servers have resulting from more vigorous knee extension from stages 3 to 6 (15).
Exercise: tennis serve shot throw
Stand assuming your normal serve ready or start position. Take a light (1-3 kg), small, medicine ball in your racket hand, and from the loading position (Figure 18, left), throw the medicine ball up and forward using a “shot-type” throwing motion. Emphasize the loading position through knee flexion and trunk rotation and lateral bend as pictured. The explosive nature of this exercise will carry the athlete upward and forward into the court (Figure 18).
FOLLOW-THROUGH PHASE—DECELERATION STAGE (STAGE 7)
The deceleration stage (Figure 19) of the service motion is one of the most violent stages of the tennis service motion, and the majority of injury prevention training should focus on developing the upper-body deceleration mechanics and muscles that help optimize this portion of the service motion. The left internal oblique was more active than the right internal oblique throughout a serve—except during the deceleration stage (4). The deceleration force between the trunk and the arm during the deceleration stage can be 300 N or higher. This force is required to stabilize and support the shoulder against the distraction forces that can equal 0.5 to 0.75 times the body weight or more (6). To stabilize the trunk during an unbalanced posture (i.e., the deceleration phase), the right erector spinae becomes highly active during the deceleration phase (4).
The follow-through phase is characterized by a moderately high activity of the posterior rotator cuff, serratus anterior, biceps brachii, deltoid, and latissimus dorsi musculature. The posterior rotator cuff activation levels range between 30 and 35% maximum voluntary isometric contraction as the humerus is decelerated after contact (28). This is needed to maintain glenohumeral stability and offset the distraction forces incurred during the follow-through phase.
Exercise: deceleration stage
Stand facing the attachment point of the elastic tubing that should be at just above waist level. Abduct the shoulder 90° and keep the elbow flexed 90° throughout the performance of this exercise. Start from a position of 90° of external rotation (Figure 20) with moderate tension in the tubing. The arm will be slightly forward as pictured to place it in the scapular plane. From this position, rapidly move the arm into internal rotation until the forearm is parallel to the ground. When this horizontal position is achieved, immediately move the arm back into external rotation until a vertical forearm position is maintained. Hold that position for a count of 2 seconds and then repeat the rapid exchange again. Perform several sets of 10-15 repetitions to fatigue the posterior rotator cuff. Note that until the exercise movement can be optimally isolated (humeral rotation), it may be helpful to support the exercising arm's elbow with the opposite hand to keep 90° of abduction.
FOLLOW-THROUGH PHASE—FINISH STAGE (STAGE 8)
Landing mechanics after the serve (Figure 21) are a very important component because this is where the majority of lower-body/core eccentric loading occurs. The finish stage does not influence the performance of the serve, but it is vital in the “shock-absorption” during the landing. If this stage is not performed appropriately, greater stress will be imparted on the entire body and could, in the opinion of the authors, increase the likelihood of loading related injuries.
Exercise: jump into single-leg RDL
This is a modification of a traditional single-leg Romanian Deadlift (RDL) exercise. The only difference is that the athlete takes a small forward jump into the single-leg RDL movement to simulate the landing mechanics and movement that needs to be strengthened to handle the thousands of serves that a tennis player will hit during a year (Figure 22).
The tennis serve is a very complex and important tennis stroke. The purpose of this article was to provide an 8-stage performance evaluation of the tennis serve with specific exercise suggestions to improve certain areas of weakness from a strength, power, flexibility, and muscular endurance perspective.
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