An 8-Stage Model for Evaluating the Tennis Serve
An 8-Stage Model for Evaluating the Tennis Serve Implications for Performance Enhancement and Injury Prevention Mark Kovacs, PhD, CSCS*† and Todd Ellenbecker, DPT, MS, SCS, OCS, CSCS‡‖
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Abstract Background: The tennis serve is a complex stroke characterized by a series of segmental rotations involving the entire kinetic chain. Many overhead athletes use a basic 6-stage throwing model; however, the tennis serve does provide some differences.
Evidence Acquisition: To support the present 8-stage descriptive model, data were gathered from PubMed and SPORTDiscus databases using keywords tennis and serve for publications between 1980 and 2010.
Results: An 8-stage model of analysis for the tennis serve that includes 3 distinct phases—preparation, acceleration, and follow-through—provides a more tennis-specific analysis than that previously presented in the clinical tennis literature. When a serve is evaluated, the total body perspective is just as important as the individual segments alone.
Conclusion: The 8-stage model provides a more in-depth analysis that should be utilized in all tennis players to help better understand areas of weakness, potential areas of injury, as well as components that can be improved for greater performance.
Keywords: biomechanics, serve, tennis, kinetic chain The tennis serve is the most complex stroke in competitive tennis.32 The complexity of the movement results from the combination of limb and joint movements required to summate and transfer forces from the ground up through the kinetic chain and out into the ball. Effective servers maximally utilize their entire kinetic chain via the synchronous use of selective muscle groups, segmental rotations, and coordinated lower extremity muscle activation (quadriceps, hamstrings, and hip rotators, internal and external). This lower body–core force production is then transferred up into the upper body and out through the racket into the ball. If any of the links in the chain are not synchronized effectively, the outcome of the serve will not be optimal.38
The serve has been studied in a similar manner to the throwing motion in baseball, although some significant differences do exist between the serving motion and the throwing motion. These differences include planes of motion, the non dominant arm tossing the tennis ball, the trajectory of forces produced and released, the tennis racket (which alters the lever arm), the technical components of the serve, and the variety of placements and goals of the motion (spin, speed, angle, direction, etc).
The components usually seen in the traditional throwing analysis30,35 have been altered in this proposed 8-stage tennis-specific serve model (Figure 1). The 8-stage model has 3 distinct phases: preparation, acceleration, and follow-through. Each stage is a direct result of muscle activation and technical adjustments made in the previous stage. When a serve is evaluated, the total body perspective is just as important as the individual segments alone.
The 3 phases and 8 stages of the tennis serve.
The Kinetic Chain And The Tennis Service Motion Over a quarter century ago, the kinetic chain was first studied in nationally ranked tennis players.25 Players increase the maximum linear velocity from the knee to the racquet.25 The preparation phase (stages 1-4) results in the storing of potential energy that can be utilized as kinetic energy during the acceleration phase. In an efficiently functioning kinetic chain, the legs and trunk segments are the engine for the development of force and the stable proximal base for distal mobility.26,37,58 This link develops 51% to 55% of the kinetic energy and force delivered to the hand.37This link also creates the back-leg-to-front-leg angular momentum to drive the arm up and forward.33,55 The large cross-sectional area of the legs and trunk, with its large mass and high moment of inertia, creates an anchor that allows for centripetal motion to occur.10,58 An analysis of the kinetic chain using mathematical modeling revealed that a 20% reduction in kinetic energy from the trunk requires a 34% increase in velocity or a 70% increase in mass to achieve the same kinetic energy to the hand.37These data highlight the importance of developing effective lower body force and efficient energy transfer up through the kinetic chain.
The 3 Major Types Of Serves In Tennis The 3 major types of serves used in tennis are the flat (limited spin), slice (sidespin), and topspin “kick” serves (Figure 2). It is important to understand the differences in these serves and how they may affect the kinetic chain muscle activation patterns and summation of forces. There is an inverse relationship between speed of serves and spin rate (Figure 3). The lower body does not show major differences in the 3 serves. The hypothesis that greater lower trunk muscle activation occurs in topspin (kick) serves has not been supported.7 No major differences were found in 8 lower trunk muscles during flat, topspin, and slice serves. However, bilateral differences in muscle activation were more pronounced in the rectus abdominis and external oblique than in internal oblique and lumbar erector spinae muscles.8
The 3 major types of tennis serves (a right-handed server).
Speed versus spin comparisons among flat, slice, and topspin (kick) serves. Data adapted from Elliott et al22 and Sakurai et al.53
The major differences seen in serves occur higher in the kinetic chain—namely, at the racket face angle, as determined by forearm pronation and internal shoulder rotation.22
The 8-Stage Model The 8-stage model has 3 distinct phases: preparation, acceleration, and follow-through. The phases reflect the distinct dynamic functions of the serve: store energy (preparation phase), release energy (acceleration phase), and deceleration (follow-through phase).
Phase 1: Start The start of a player’s serve (Figure 4) reflects style and individual tendency rather than substance. Muscular activation in the shoulder and scapular regions is very low during this phase because demand is low.52 The goal of the start is to align the body to utilize the ground for force/power generation throughout the service motion.
Preparation phase. Stage 1: Start.
Phase 2: Release This stage occurs in an instant when the ball is released from the nondominant hand (left) (Figure 5). Muscle activation is very limited in the left erector spinae during the start and release stages.7 The activity of the right erector spinae increases steadily from the beginning of the serve through the end.7 The location of the toss relative to the player affects arm abduction and subacromial humeral position. The toss should be out slightly lateral to the overhead position of the server, facilitating ball contact at approximately 100° of arm abduction.29Improper toss location too close to the head (12 o’clock position) can increase arm abduction and cause subacromial impingement.28 Trunk position and toss location are factors in shoulder pain during the acceleration and contact phases of the tennis serve.12
Preparation phase. Stage 2: Release.
Phase 3: Loading Loading positions the body segments to generate potential energy (Figure 6). There are 2 broad types of lower body loading (foot position) options: the foot-up (Figure 7) or the foot-back (Figure 8) techniqu