Download Biomechanics of the Forehand Stroke

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 semiwestern 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.
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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 prestretching 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.
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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 (47 o)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 stroke 1,10. 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
1. Knudson, D. (1991). The tennis topspin forehand drive: Technique changes and critical elements.
Strategies, 5(1), 19-22.
2. Brody, H. The influence of racket technology on tennis. USPTR, 1997.
3. Baker, J. A. & Putnam, C. A. (1979). Tennis racket and ball responses during impact under clamped and
freestanding conditions. Res. Q, 50, 164-170.
4. Grabiner, M. D., Groppel, J. L. & Campbell, K. R. (1983). Resultant tennis ball velocity as a function of offcenter impact and grip firmness. Med. Sci. Sports, 15, 542-544.
5. Elliott, B. C. (1982). Tennis: the influence of grip firmness on reaction impulse and rebound velocity. Med.
Sci. Sports, 14, 348-352.
6. Brody, H. (1987). Tennis science for tennis players. University of Pennsylvania Press, Philadelphia, PA.
7. Knudson, D. V. & White, S. C. (1989). Forces on the hand on the tennis forehand drive: Application of
force sensing resistors. Int J Sport Biomech, 5 , 324-331.
8. Knudson, D. V. (1991). Factors affecting force loading on the hand in the tennis forehand. J Sports Med
Phys Fit, 31(4), 527-331.
9. Elliott, B., Kotara, T. & Noffal, G. (`1997). The influence of grip position on upper limb contribution to
racket head velocity in a tennis forehand. J Applied Biomech, 13, 182-196.
10. Groppel, J. (1984). Tennis for Advanced Players. Human Kinetics: Champaign, Illinois.
11. Bahamonde, R. E. & Knudson, D. (1998). Upper extremity kinetics of the open and close stance
forehand. 4th International Conference on Sports Medicine and Science in Tennis, Coral Gables, Florida.
12. Bahamonde, R. E. & Knudson, D. (1998). Kinematic analysis of the open and square stance tennis
forehand. Med. Sci. Sports, 30(5), s29.
13. Elliott, B., Marsh, T. & Overheu, P. (1987). The mechanics of the Lendl and conventional tennis
forehands: A coach's perpective. Sports Coach, Oct/Dec, 4-9.
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, 350-364
15. 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.