Biomechanics of the Forehand Stroke

Rafael Bahamonde Indiana University, USA

Introduction

The tennis forehand stroke has changed drastically over the last 10 years. Today's players seldom use the traditional forehand. Instead, the majority of the top amateur and professional players use the modern topspin forehand stroke. Changes in the forehand technique have been attributed to new racket designs1,2. Rackets are bigger, lighter, and stiffer than the traditional wooden rackets allowing the players to hit the ball with more power and control. These changes in the forehand technique have influenced the type of grip, footwork and racket backswing and forward swing of today's tennis players.

.Preparation

The Grip: The functions of the grip are to provide the proper racket orientation at impact, place the wrist in a favorable strength position, and, depending on the type of stroke used, allow for hand mobility1. Most researchers agree that grip firmness is a crucial factor for off-center impacts.4-6,10 Most tennis professionals advocate the use of a western or semi-western grip instead of the traditional eastern forehand grip. The western grips are preferred because it is easier to generate topspin and maintain racket orientation at impact. One disadvantage of the western grip is that it is difficult for players to hit low bouncing balls. Other researchers promote the use of the eastern forehand grip highlighting that it provides for greater wrist stability and allows the players to achieve the proper racket orientation at impact regardless of ball height1. In a study by Elliott et al9. the effects of using the eastern and western forehand grips on the rotational contribution of the upper limb segments to racket head velocity were investigated. Players using the western grip were able to produce higher forward (toward the court) and sideways (along the baseline) velocities than the players using the eastern forehand grip.

The Stance: Today's players must react faster and are forced to hit on the run due to the power developed in the groundstrokes and the serves. Hence, they adopt an open stance. The traditional square stance takes longer to execute but it generates linear momentum; as the player steps forward toward the ball, and angular momentum; from the rotation of the legs, hips, and trunk10-12. In contrast, in the open stance there is little or no transfer of linear momentum since the step is taken side ways, and only the segment rotations are used to generate power for the forward swing.

.The Backswing

Another point of controversy among players, coaches, and tennis professionals has been which type of backswing provides more racket velocity and control. It was thought that the traditional straight backswing provided more control, and the loop (large and small) backswings provided greater racket velocity. Although a large-loop backswing has been

shown to increase racket velocity, racket control and timing are more likely to be affected1,10. In contrast, the small-loop backswing seemed to increase racket velocity without affecting the timing and control of the stroke10. Regardless of the type of backswing used, for more power and efficiency, the transition between the backswing and forward swing should be a fluid motion since it enhances the player's ability to utilize the pre-stretching of the muscles.

.The Forward Swing

The type of forward swing has also been modified by the changes in the game. Many of the top professional players use a multi-segment forehand technique in which individual segments of the upper extremity are used to generate racket velocity. In contrast, in the conventional forward swing the segments of the upper extremity move as a single unit from the shoulder. Research by Elliott et al14 revealed no major differences in the type of grip or initial footwork preferred by the players using multi-segment or single unit forehand swing. Clear differences were observed during the backswing phase; the multi-segment group had a more compact arm, and later, during the forward swing, generated higher racket velocities (22.5 m/s) than the single unit group (19.3 m/s) resulting in greater ball velocities.

.Racket Trajectory and Orientation

Aside from the differences in the type of stance, grip, and/or forward swing, the key elements in the topspin forehand stroke are the stroke arc and the racket orientation at impact. The trajectory of the racket (stroke arc) can be separated into horizontal and vertical planes. Most researchers agree that the horizontal motion of the racket should resemble a flattened arc near impact 6,13. The optimum angle of the racket in the vertical plane has been suggested to be 28o 1,10. This angle provides good spin production and speed. Smaller angles tend to produce less spin while larger angles sacrifice ball speed and the depth of the shot. Changes in footwork and type of forward swing can influence the stroke arc. For instance, the use of the multi-segment forehand swing produces a smaller stroke arc and a steep vertical trajectory at impact (47o)10. According to Brody a smaller stroke arc is less accurate since it reduces the margin of error due to the smaller swing radius6. Most researchers agree that hitting with an open stance is not more efficient but is the result of lack of preparation time for the forehand stroke1,10. Research by Knudson and Bahamonde15 showed that the closed stance allowed a group of teaching professionals to maintain a more accurate racket path in the horizontal plane. When the players used an open stance it resulted in a 60% reduction in the time in which the ball could be successfully hit on the racket face in the horizontal plane.

.Linear and Angular Momentum

One of the most common concerns of tennis players is how to develop more power and control on the forehand stroke. Both power and control can be achieved through the proper development of linear and angular momentum. Linear momentum is the quantity of linear motion that a body possesses. In the forehand stroke, linear momentum is developed through the forces generated from the ground as you step forward and transfer your body weight from the back leg to the forward leg (for a closed stance footwork)10. Angular momentum is the

quantity of angular motion that a body possesses. Angular momentum is also developed from the ground reaction forces (GRF) and tends to produce a sequence of body rotations (legs, hips, trunk, upper limb, and racket)10. Optimal trunk rotation is one of the outcomes of angular momentum. It has been shown that trunk rotation is significantly correlated with racket velocity regardless of the type of stance used or skill level (professionals or intermediates)12. The rotation of the trunk not only contributes to the racket velocity (about 10% of final racket velocity) but is also used in the pre-stretching of the shoulder muscles to allow them to produce a larger tension.

.Conclusion

What can coaches or players do to produce explosive forehands? Coaches and players need to understand the basic biomechanical principles and how to apply them to the different components of the strokes. There is no doubt that one of the most important sources of power for a tennis player comes from the racket. The new rackets not only allow the players to hit ball harder, they also provide more control. A firm grip near impact is necessary to control the racket during off-centre hits. Use a square stance whenever possible, it not only seems to be more effective in generating linear and angular momentum but it also seems to produce a more accurate racket path. Try to develop a smooth and continuous small-loop backswing. Select the forward swing (multi-segment or single unit forehand) that best suits the player's physical and motor skill abilities. Regardless of the type of forward swing, stress the importance of using trunk rotation and the legs throughout the forehand stroke and explain to the players the importance of a proper follow-through.

 

References

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14. Elliott, B., Marsh, T. & Overheu, P. (1989). A biomechanical comparison of the multi-segment and single unit topspin forehand drives in tennis. Int J Sports Biomech, 5, 350-36415. Knudson, D. & Bahamonde, R. E. (1998). Impact kinematics of the open and square stance tennis forehand. 4th International Conference on Sports Medicine and Science in Tennis, Coral Gables, Florida.