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Biomechanics of the Tennis Groundstrokes: Implications for Strength Training

Roetert, E Paul, PhD1; Kovacs, Mark, PhD, CSCS1; Knudson, Duane, PhD2; Groppel, Jack L, PhD3

Strength & Conditioning Journal: August 2009 - Volume 31 - Issue 4 - p 41-49
doi: 10.1519/SSC.0b013e3181aff0c3
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THE PURPOSE OF THIS ARTICLE WAS TO SUMMARIZE RECENT RESEARCH RELATED TO THE BIOMECHANICS OF TENNIS TECHNIQUE IN GROUNDSTROKES AND THEN TO RECOMMEND SPECIFIC STRENGTH AND CONDITIONING EXERCISES THAT WOULD TEND TO IMPROVE TENNIS PERFORMANCE AND PREVENT INJURY. BASED ON THE AVAILABLE RESEARCH, IT WAS DETERMINED THAT TRAINING EXERCISES SHOULD EMULATE THE SEQUENTIAL COORDINATION INVOLVED IN GROUND STROKE PRODUCTION, AS WELL AS STABILIZING MUSCULATURE THAT MIGHT BE INVOLVED IN DEVELOPING FORCE OR IN PROTECTING BODY PARTS FROM STRESSFUL ACTIONS. SPECIFIC EXERCISES BASED ON THE FINDINGS IN THE RESEARCH LITERATURE WERE THEN OFFERED.

1United States Tennis Association, Boca Raton, Florida; 2Department of Health and Human Performance, San Marcos, Texas; and 3Human Performance Institute, Lake Nona, Florida

E. Paul Roetertis Managing Director of Coaching Education and Sport Science at the United States Tennis Association.

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Mark Kovacsis Senior Manager of Strength and Conditioning/ Sport Science at the United States Tennis Association.

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Duane Knudsonis Chair of the department of Health and Human Performance at Texas State University.

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Jack Groppelis co-founder of the Human Performance Institute.

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INTRODUCTION

The game of tennis has changed dramatically in the past 30 years. This is probably most evident in groundstroke technique and strategy. Modern players often hit aggressive high-speed groundstrokes to overpower their opponent. This strategy places extra stress on the player's body that strength and conditioning professionals should consider in designing training programs. This article will summarize recent research related to the biomechanics of tennis technique and propose specific conditioning exercises that logically would tend to improve performance and reduce the risk of injury in tennis.

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CHANGES IN TECHNIQUE

Traditional tennis groundstrokes were hit from a square or closed stance with a long flowing stroke using simultaneous coordination of the body. The modern forehand and even the backhand (particularly the 2-handed backhand) are more often hit from an open stance using sequential coordination of the body. Elite tennis always had these 2 styles of groundstrokes (1), but since that time, there has been a reversal from primarily simultaneous to sequential groundstroke technique. This change in the coordinated use of the “kinetic chain” suggests that the loading and injury risk to major segments of the body may have changed in tennis (11).

It is not possible to uniquely track the transfer of mechanical energy in a 3-dimensional movement of the human body, but it is generally accepted that most of the energy or force used to accelerate a tennis racket is transferred to the arm and racket from the larger muscle groups in the legs and trunk (5,15,21). While it is believed that optimal use of the kinetic chain will maximize performance and reduce the risk of injury (6,11), the transfer of force and energy to the small segments and tissues of the upper extremity do place them under great stress. For example, medial elbow pain is on the rise in tennis players most likely because of the transfer of energy from the legs and trunk in forehands and serves. This focuses stress on the medial elbow region in the bent-arm sequential coordination in these strokes. The next sections will summarize recent research on technique issues specific to each groundstroke that are important to consider when planning conditioning programs. Several reviews of the biomechanics of tennis are available for interested readers (5,15,18).

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FOREHAND

Vigorous extension of the lower extremity in classic closed stance forehands creates greater axial torques to rotate the pelvis and hips than not using the legs (9). While this transfer of energy has not been tested in open stance forehands, it is logical that vigorous leg drive also transfers energy to trunk rotation. Knudson and Bahamonde (16) reported nonsignificant differences in racket path and speed at impact between open and square stance forehands of tennis teaching professionals. As stated by Roetert and Reid (20), there are 2 things to remember related to these forehand stances: (a) open stances are often situation specific and (b) both stances use linear and angular momentum to power the stroke. Situation-specific forehands refer to the need to produce different types of forehands depending on where the player is in the court, the purpose of the shot (tactics), amount of preparation time available, as well as where the opponent is during the same scenario. Tennis players need to create differing amounts of force, spin, and ball trajectories from a variety of positions, and this has resulted in adaptations of stroke mechanics and stances. The most common situations where open stance forehands are applied include wide and deep balls when the player is behind the baseline or requires greater leverage to produce the stroke.

Vigorous axial hip and upper-trunk rotation allow for energy transfer from the lower extremity to the upper extremity in the square stance forehand. The upper trunk tends to counter-rotate about 90 to 100° from parallel to the baseline and about 30° beyond the hip in the transverse plane (22) in preparation for the stroke. Forward axial torque to rotate the hips achieves its peak at the initiation of the forward stroke (8). Forward rotation of the upper trunk coincides with a lag in the upper extremity resisted by eccentric muscle actions and large peak shoulder horizontal adductor and internal rotation torques (3). Well-coordinated sequential rotations up the kinetic chain through the trunk and upper extremity take advantage of the stretch-shortening cycle of muscle actions.

The forearm flexors and grip musculature are also important in the tennis forehand. Not because these muscles create a great deal of joint rotation to accelerate the racket (4) or because grip forces increase ball impulse (13), but because the energy from the lower body and trunk must be transferred to the racket in the later stages of the stroke. In fact, the preferred style of grip and height of the ball at impact used by the player significantly affects the potential contribution of the hand/wrist rotation to racket speed (4). The main kinetic chain motions that create racket speed in the forehand are trunk rotation, horizontal shoulder adduction, and internal rotation (4). Modern forehand technique (typically utilizing grips ranging between eastern and western grips) clearly involves sequential coordination that takes advantage of stretch-shortening cycle muscle actions. Training exercises should, therefore, emulate this sequential coordination, as well as stabilizing musculature. Following impact in all tennis strokes, the racket and arm retain the vast majority of the kinetic energy from before impact, so the eccentric strength of the musculature active in the follow-through should also be trained. Eccentric strength both in the upper and in the lower body can assist in maximizing tennis performance as well as to aid in the prevention of injuries (12). Particularly, the catching phase of the medicine ball (MB) tosses in Figures 4-7 helps in improving both upper- and lower-body eccentric strength.

Figure 4

Figure 4

Figure 5

Figure 5

Figure 6

Figure 6

Figure 7

Figure 7

Figure 1a-c show the preparation phase of the open stance forehand. The player's weight transfer from his right leg to his left leg (he is left handed) shows the horizontal linear momentum used to preload the left leg for a stretch-shortening cycle action to initiate the stroke. Some of the energy stored in this leg is converted to predominantly upward (vertical linear) momentum but also forward (horizontal linear) momentum. This leg drive utilizes ground reaction forces and is critical for linear to angular momentum transfer and the development of high racket speed. In Figure 1d-f, we can see the forward swing. The pronounced hip and shoulder rotation from Figure 1c-f is evidence of the use of angular momentum. Energy from the left leg is transferred as the hips open up first, followed by the shoulders. The completion of the swing shows a follow-through in the direction of the target until well after contact is made followed by the racket swinging back over the head as a result of the forceful rotational component of the swing. This follow-through, where the racket actually finishes over the head, is an adaptation that many players have implemented, and although the follow-through is initially still toward the target (Figure 1e), the overall pathway of the stroke (Figure 1f) ending up over the shoulder allows the player to impart greater spin on the ball. This adaptation is partially the result of technology changes in the tennis racket and strings allowing for more power and spin generation resulting in more margins for error on the strokes.

Figure 1

Figure 1

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ONE-HANDED AND TWO-HANDED BACKHAND

Training the wrist extensors is particularly important for tennis players using a 1-handed backhand. Torques about the wrist in 1-handed backhands are greater than direct force loading (14) and can create a rapid stretch of the wrist extensors that is more pronounced in players with a history of tennis elbow (17). This is strong retrospective evidence that training of the wrist extensors and grip may be useful to reduce the risk of the common overuse injury of the lateral epicondyle.

There are differences in the use of the legs, trunk, and upper extremity between the 1- and 2-handed backhands. One-handed backhands have the hitting shoulder in front of the body and rely less on trunk rotation and more on coordinated shoulder and forearm rotations to create the stroke (Figure 2a-f). Front-leg extensor torques are larger in the 1-handed backhand than the 2-handed backhand (19). Two-handed backhands have larger extension torques in the rear leg, which result in larger axial torques to rotate the hips and trunk than 1-handed backhands (2,10,19). Greater upper-trunk rotation has been observed in 2-handed backhands than in 1-handed backhands (19). Note the hip and trunk rotation in the 2-handed backhand (Figure 3a-f).

Figure 2

Figure 2

Figure 3

Figure 3

Despite these differences, skilled players can create similar levels of racket speed at impact in 1- and 2-handed backhands (19). In general, there are 2 styles of coordination in 2-handed backhands. One essentially involves straight arms and 4 major kinetic chain elements (hips, trunk, shoulder, and wrist), while the other adds rotations at the forearm (7,19). Whatever the technique adopted, the strength and conditioning professional should work with the tennis coach to customize training programs for the specific techniques used by players.

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EXERCISES

Examples are described for forehands (right-handed players), but they should also be performed on the opposing side to mimic movements required for backhand strokes.

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MEDICINE BALL DEEP GROUNDSTROKE

The purpose was to train the athlete to move efficiently to deep balls behind the baseline and to be able to produce greater energy transfer from open stance position that will translate into greater weight transfer, trunk rotation, and more effective stroke production from deep in the court (Figure 4).

The athlete starts on the center service mark and the coach/trainer throws the MB about 3 to 5 feet behind and to the right. The athlete will need to move back and across quickly to catch the MB (loading phase) and then while maintaining dynamic balance produce a forceful hip turn and throw that will mimic the muscle contractions and movements required for a deep defensive forehand stroke (for a right-hander).

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MEDICINE BALL SHORT GROUNDSTROKE

The purpose was to train the athlete to move forward and in a balanced fashion transfer energy from the lower extremities (open or square stance) to weight transfer and hip/trunk rotation for more effective stroke production (Figure 5). In Figure 5, the athlete is demonstrating a closed stance catching position. This movement can also be performed using an open stance catching position.

The athlete starts on the center service line and the coach/trainer throws the MB about 3 to 5 feet in front and to the athlete's right. The athlete will need to move forward and across quickly to catch the MB (loading phase) and then while maintaining dynamic balance produce a forceful hip and trunk rotation to throw the MB. This will mimic the movement and muscles used during a short attacking forehand.

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MEDICINE BALL WIDE

The purpose was to train the athlete to move sideways and to be able to produce greater energy transfer from an open stance position (Figure 6). This position will produce greater weight transfer, trunk rotation, and more effective stroke production on wide balls.

The athlete starts on the center service line and the coach/trainer throws the MB about 5 feet to the right of the athlete. The athlete will need to move laterally (utilizing either the shuffle or the crossover step) to catch the MB (loading phase) and then while maintaining dynamic balance produce a forceful hip and trunk rotation to throw the MB. This movement sequence will mimic the movement and muscles used in a wide forehand.

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MEDICINE BALL WALL OPEN STANCE

The purpose was to develop rotational hip and core strength in movement patterns and planes that are most used during tennis strokes (Figure 7).

The athlete starts about 5 to 8 feet from a solid wall and loads the hips and core while also putting the oblique muscles on stretch. From this loading position (Figure 7 demonstrates an open stance loading position), the athlete forcefully rotates the hip and upper body to release the MB as hard as possible against the wall.

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CABLE ROTATION IN THE TRANSVERSE PLANE

The purpose was to develop rotational core strength in the transverse plane (Figure 8).

Figure 8

Figure 8

The athlete grasps the handle of a cable pulley machine at the height of the waist. The athlete takes 3 to 5 steps from the machine to increase the tension and lowers the body into a quarter squat position. From this position, the athlete slowly rotates through the transverse plane as far as the athlete's flexibility allows. This movement is then repeated on the way back to the starting position focused on developing deceleration ability in this same plane of motion.

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WRIST ROLLER

The purpose was to increase grip strength and endurance via forearm flexion and extension (Figure 9).

Figure 9

Figure 9

The athlete grasps the wrist roller device with both hands at shoulder height. The athlete flexes and extends the wrist to lower the weight. Once the weight is lowered as far as possible, the athlete then flexes and extends the wrist to lift the weight back up to the starting position.

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WEIGHTED FOREARM PRONATION AND SUPINATION

The purpose was to develop forearm strength and endurance in pronation and supination (Figure 10).

Figure 10

Figure 10

The athlete places their forearm on a table or bench while grasping a head heavy instrument (a weighted bar and hammer are both good options). Figure 10a demonstrates a forearm pronation movement, and Figure 10b demonstrates a forearm supination movement. Both these movements are used during tennis groundstrokes.

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SUMMARY AND APPLICATIONS FOR COACHES

The purpose of this article was to help coaches recognize the unique aspects of tennis groundstrokes, with specific implication for how they can train their athletes. Again, the 2-fold approach of this article was to help practitioners realize the types of training that will (a) improve performance by creating more force within muscle groups, improve coordination between various body parts involved in each stroke, and develop overall power in the athlete's stroke production and (b) develop strength in the various body parts and across joints that would protect the athlete from injury.

Practical exercises have been offered that will emulate the stroke coordination to improve the efficiency of stroke production as well as exercises that will improve the athlete's ability to decelerate specific body parts to assist in recovery after the execution of the specific stroke. The exercises denoted in this article are designed to help the coach with on-court and off-court training so that various training sites can be utilized for effectiveness in training. For example, MB drills are offered to help the athlete, not only move and get in position properly but also to execute the form of the stroke in the proper pattern. Coordination of body weight transfer is discussed as well.

Finally, there is a demonstration of how the legs, hips, and torso should move in synchrony as well as instruction on how to develop coordination so the athlete can utilize the kinetic chain more effectively. It is anticipated that coaches will be able to provide a safer yet more productive and effective strength training regimen for their athletes.

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REFERENCES

1. Ariel GB and Braden V. Biomechanical analysis of ballistic vs. tracking movements in tennis skills. In: Proceedings of a National Symposium on the Racquet Sports. Groppel J, ed. Champaign, IL: University of Illinois, 1979. pp. 105-124.
2. Akutagawa S and Kojima T. Trunk rotation torques through the hip joints during the one-and two-handed backhand tennis strokes. J Sport Sci 23: 781-793, 2005.
3. Bahamonde R and Knudson D. Kinetics of the upper extremity in the open and square stance tennis forehand. J Sci Med Sport 6: 88-101, 2003.
4. Elliott B, Takahashi K, and Noffal G. The influence of grip position on the upper limb contributions to racket-head speed in the tennis forehand. J Appl Biomech 13: 182-196, 1997.
5. Elliott B. Biomechanics of tennis. In: Tennis. Renstrom AFH, ed. Osney Mead, Oxford: Blackwell Science, 2002. pp. 1-28.
6. Elliott B. Biomechanics and tennis. Br J Sports Med 40: 392-396, 2006.
7. Groppel J. High Tech Tennis (2nd ed.). Champaign, IL: Human Kinetics, 1992, 107.
8. Iino Y and Kojima T. Torque acting on the pelvis about its superior-inferior axis through the hip joints during a tennis forehand stroke. J Hum Mov Stud 40: 269-290, 2001.
9. Iino Y and Kojima T. Role of knee flexion and extension for rotating the trunk in a tennis forehand stroke. J Hum Mov Stud 45: 133-152, 2003.
10. Kawasaki S, Imai S, Inaoka H, Masuda T, Ishida A, Okawa A, and Shinomiya K. The lower lumbar spine moment and the axial rotation motion of a body during one-handed and double-handed backhand stroke in tennis. Int J Sports Med 26: 617-621, 2005.
11. Kibler WB. Kinetic chain contributions to elbow function and dysfunction in sports. Clin Sports Med 23: 545-552, 2004.
12. Kovacs MS, Roetert EP, and Ellenbecker TS. Efficient deceleration: The forgotten factor in tennis-specific training. J Strength Cond Res 30: 58-69, 2008.
13. Knudson D. Hand forces and impact effectiveness in the tennis forehand. J Hum Mov Stud 17: 1-7, 1989.
14. Knudson D. Forces on the hand in the one-handed backhand. Int J Sports Biomech 7: 282-292, 1991.
15. Knudson D. Biomechanical Principles of Tennis Technique. Vista, CA: Racquet Tech Publishing, 2006. pp. 10.
16. Knudson D and Bahamonde R. Trunk and racket kinematics at impact in the open and square stance tennis forehand. Biol Sport 16: 3-10, 1999.
17. Knudson D and Blackwell J. Upper extremity angular kinematics of the one-handed backhand drive in tennis players with and without tennis elbow. Int J Sports Med 18: 79-81, 1997.
18. Knudson D and Elliott BC. Biomechanics of tennis strokes. In: Biomedical Engineering Principles in Sports. Hung GK and Pallis JM, eds. New York, NY: Kluwer Academic/Plenum Publishers, 2004. pp. 153-181.
19. Reid M and Elliott B. The one- and two-handed backhand in tennis. Sport Biomech 1: 47-68, 2002.
20. Roetert EP and Reid M. Linear and angular momentum. United States Tennis Association: High Performance Coaching Newsletter. 9(3): 5-8, 2008.
21. Schönborn R. Advanced Techniques for Competitive Tennis. Achen, Germany: Meyer and Meyer, 1999. pp. 26.
22. Takahashi K, Elliott B, and Noffal G. The role of upper limb segment rotations in the development of spin in the tennis forehand. J Sci Med Sport 28: 106-113, 1996.
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Keywords:

kinetic chain;; tennis-specific training; technique analysis

© 2009 by the National Strength & Conditioning Association