Michelle
Brown
Dr. Tim
Hopper
11/09/01
#0021366
Video Analysis – Forehand Stroke
Although the forehand stroke is one of the most basic strokes in tennis, several key elements create a powerful, dynamic shot that can develop a successful game of tennis. All top players follow a similar procedure, “they move and prepare early, watch the ball closely, transfer their weight into the shot by stepping to hit, meet the ball with a square racket, hit through the ball low to high, and finish high with the full follow-through.” (Claxton, 1999). These features are shown in all top class athletes because these athletes have “been coached to use good mechanics. Their coaches have taught them to use actions in their performances that produce the optimal force, velocity, spin, required by the skill.” (Carr, 1997). Using a high-speed video camera, my forehand stroke was captured and will be analyzed as a comparison/contrast to Venus Williams, a professional female tennis player. Following biomechanics techniques, breaking down key phases (group of movements that appear to stand on their own, which the athlete joins together in the performance of the total skill), the preparation, wind-up, force-generation, and follow-through/recovery will give a clear indication on improving my performance. “Each phase, starting from the preparatory movements, leads into and influences the next phase in line like a chain reaction. This common characteristic tells you that errors occurring during an early phase of a skill are bound to affect all the phases that follow.” (Carr, 1997).
The initial phase in performing the forehand stroke is the preparation. Early preparation is a fundamental element in achieving timing, accuracy, and control. The beginning of preparation occurs before the opponent makes his/her shot. “Stand about one step behind the baseline with a slight forward lean so that your heels are lightly on the ground or slightly raised. The slight lean prepares you for quick movement in a variety of directions to attack the ball.” (Claxton, 1999). Starting from the ready position (feet comfortably spread a little more than shoulder-width apart, knees bent – locked knees must be unlocked before quick movement can take place, body relaxed, and weight slightly forward on the balls of the feet) the player creates elastic energy. The stored energy provides the means for work to be done. The ready position “is a dynamic, not a static position, with the player constantly alert and prepared to move quickly in any direction.” (Johnson & Xanthos, 1997). “In dynamic skills, muscle contractions produce actions.” (Carr, 1997).
The key to the preparation is to be ready for action. Hold the racket loosely with the dominant hand using the Eastern forehand grip. Keep the head of the racket above the wrist, pointing slightly upward, about waist high. To achieve this grip, “shake hands with your racket. Spread the fingers, making certain that the index finger is apart from the middle finger and is bent. Wrap your thumb around the grip until it touches the outside of your middle finger.” (Johnson & Xanthos, 1997).
It is clear in Venus Williams’ preparatory phase (professional figures 1 and 2), that the correct use of biomechanics techniques will promote a successful forehand stroke. Venus begins by creating elastic energy by standing with a slightly forward lean and her weight on the balls of her feet. This position clearly stores energy and thus produces quick actions. In addition to using the Eastern forehand grip, Venus employ’s added control on the racket by positioning the racket in the center of her body and using her non-dominant (left) hand to stabilize the racket during preparation. Although no force is placed on the racket with the non-dominant hand, the stability comes because no energy is being lost with added limb movements.
In contrast, my preparation phase (figures 1 and 2) never started with a pause behind the baseline. Because I never had a wide base, or stored elastic energy, I did not create the forceful power required to perform a quality stroke. Additionally, my racket is closed as I am running toward the ball. This type of error may result in a loss of topspin (which will be outlined during the force generation phase). Since the early phases of a skill always affect the later phases of the skill, working on the preparation is fundamental. In the future, I will concentrate on preparing earlier and thus created elastic energy. Not only will I be able to move toward the oncoming ball faster, but I will be able to successfully sense the direction of my opponent’s stroke and will be able to move into that space quickly. Although this may seem like a small change, it is essential in developing my game of tennis as a whole.
Following the preparation phase is the wind-up phase. The wind-up for the forehand stroke is the backswing. To achieve a successful backswing, “point the head of your racket in the direction of your opponent, the end of the handle close enough to your body to make the position comfortable and without tension.” (Johnson & Xanthos, 1997). As in my case, a right-handed player turns “toward the right sideline with the left side pointing toward the net and with the forward foot, hip, and shoulder directed toward the shot.” (Johnson & Xanthos, 1997). The key to a well-executed backswing is early preparation, “moving the racket back in anticipation of the forward movement to the ball contact point.” (Johnson & Xanthos, 1997). “The racket is taken back at the predicted height of ball contact. The speed with which your racket is drawn back will depend upon the speed of the oncoming ball.” (Johnson & Xanthos, 1997).
As the racket swings back, transfer the body weight to the right (back) foot. “Continue the backswing of the racket until it is pointing directly at the back fence, slightly lower than hip level. As the movement is being completed, your weight is on the back foot; move your left foot in the direction of the ball with the toe pointing toward the right net post; the head, eyes, left side, and shoulder face the net. The knees are flexed for balance.” (Johnson & Xanthos, 1997). By pointing the left arm toward the oncoming ball (simultaneous with moving the racket back), the body remains in control, the ideal hitting zone (out and in front of the body) is achieved, and the body uses the arm as a counterbalance. By stretching out the opposing arm, the muscles are stretched and “establish a position from which your athlete can apply force over a long distance or time frame.” (Carr, 1997).
The feet are spread slightly further than shoulder width apart, the wide base provides the optimal position for the center of gravity and is essential for “applying and receiving force.” (Carr, 1997). An inadequate base not only makes the athlete unstable but, equally important, “it reduces the distance and time over which the athlete can apply force.” (Carr, 1997). The ground-reaction force shows that the player pushes off of the ground with an equal and opposite force as the ground pushing off of the player. By optimizing this force, the player utilizes elastic energy to respond with a forehand stroke. Although stability is a key factor in a quality backswing, “maximum stability is not the objective, but rather a level of stability that allows your athlete to move in a flash in any direction.” (Carr, 1997). It can be shown that “stability is one turning effect (i.e., torque) battling another, and to remain stable your athlete may have to reposition his/her feet and center of gravity to apply more leverage and more torque. Force-producing actions are tremendously important in creating the desired effect in a skill.” (Carr, 1997). When the athletes muscles apply force in the “correct amount, over the correct range and time period, and in the correct sequence” (Carr, 1997), the athlete has developed the several of the keys which when combined with the force-generation phase create a dynamic tennis stroke.
As can be indicated by Venus William’s wind-up phase, (professional figure 3 and 4), a precise backswing gives the stroke power, control, and technique. As Venus successfully transfers her weight to her back (right) foot, her racket (right) arm is brought back simultaneously. Although Venus brings the racket back slightly higher than the predicted height of ball contact, (professional figure 3), she drops the racket down (professional figure 4) and thus creates the low-to-high swing that is characteristic of the topspin (which will be outlined in the force generation phase. Additionally, Venus has a wide base (slightly wider than shoulder width) that allows for utilization of the ground reaction force. Although it is difficult to indicate on the figures because of the angle of the picture, it is clear that Venus is using her non-dominant (left) arm as a counter balance. She will be able to successfully hit the ball in the ideal hitting zone because of her body position.
As a comparison to Venus Williams, my wind-up phase (figures 3 and 4), indicate that although I move my racket into a backswing position, it is not because my racket “swings” into the position (it merely moves there). I need to prepare early enough to give myself adequate time to apply biomechanics techniques to my backswing, which in-turn will promote a quality force generation phase, and thus a skillful forehand stroke. In example, as my arm is brought back, I have an extremely wide base (which results in a loss of force) and my racket arm is very extended (since longer levers require more power to generate force, I am loosing needed energy, power, and thus force). Although my wide base allows for immense stability, it is not effective because it does not promote quick movement as a result of stored elastic energy. As can be seen in figure 4, my weight has transferred to my back foot, but not to the extent of Venus Williams. Also, my non-dominant (left) arm never extends or points at the oncoming ball. Because of this, I am not going to hit the ball in the ideal hitting zone, and I am diminishing the amount of force that I can apply over a distance. It can be seen that in conjunction with the preparation phase, I need to get into position quicker. I will also focus on keeping my base slightly wider than shoulder width, and I will bring my racket back with a bent elbow, with the racket head facing the back wall. Combining these changes, along with keeping focused on transferring my weight, I will be able to improve my technique in the wind-up phase in addition to influencing the phases to come.
Leading into the third phase, the progressions of preparation and wind-up create a pinnacle in which the force-generating movements contact the tennis ball. The third phase in the forehand stroke is the force-generation phase. “As the forward swing begins, move the face of the racket so that it is behind and slightly below the expected point of impact.” (Johnson & Xanthos, 1997). Transfer your weight forward, toward the ball by pushing off from your right (back) foot and stepping forward onto your left (front) foot at a “forty-five-degree angle to the baseline with the left knee bent. At the same time, begin the forward rotation of the hips and shoulders by moving the right knee in toward the left. As your weight shifts forward and your body pivots, swing your racket forward and upward in a low-to-high path, wrist firm and still laid back, elbow moving away from the body, and arm comfortably extended.” (Johnson & Xanthos, 1997). The point of impact ideally is in the hitting zone (out and in front of the body). Combining the ideal hitting zone with the technique of topspin create a tactical advantage in tennis. “To develop good topspin, the basic approach is to start the racket head from a position behind and below the ball with either a slightly closed or square racket face. Move the racket head forward and upward through the ball, keeping the face perpendicular to the intended line of flight. Continue upward after contact, finishing high and in front of your body. The amount of topspin may be controlled by varying the angle of your low-to-high swing; that is, the greater the angle, the greater the spin.” (Johnson & Xanthos, 1997). “To initiate rotation your athlete must apply the turning effect of torque. The more spin required, the more torque your athlete has to apply.” (Carr, 1997). The purpose of the topspin is to utilize biomechanics such that a “ball that is spinning forward will drop in flight.” (Johnson & Xanthos, 1997). One negative aspect to using topspin is that “the more spin that is applied to the ball, the less speed that the ball will have.” (Johnson & Xanthos, 1997). Despite this, “the slower speed of a ball hit with spin is offset by the advantages of a greater margin of error, increased control, and increased variety in shot making.” (Johnson & Xanthos, 1997).
The sequence of events involved in contacting the ball occur in a “well-defined sequence of actions, starting from the big muscles that accelerate the athlete’s body and the athlete’s large, more massive body segments, and finishing with the high speed movement of smaller, less massive body segments.” (Carr, 1997). Ideally, if “your athlete uses the right amount of force for the right amount of time, your athlete’s limbs move at the required speed through the required range of movement. When this occurs and all muscle contractions are sequenced correctly, you’ll see movements that are fluid, smooth, rhythmic, graceful, and well coordinated. When an athlete applies force indiscriminately and hap-hazardly, you’ll see actions that are jerky and awkward.” (Carr, 1997).
The momentum of the tennis racket is affected by the cocking and uncocking the wrist. Cocking the wrist causes the head of the racket to be moving through the swing faster than the arm with which it is being driven. Thus, cocking of the wrist “causes the whiplash or flail-like action of the high speed tip segments of a whip. When the wrist is cocked, it acts as an additional axis around which the racket can rotate. The velocity developed from the swing (and length) of the tennis player’s arm is multiplied along the length of the tennis racket. Without the cocking and uncocking action, the arms and racket move as a fixed unit. This would not allow the head of the racket to reach optimal velocity.” (Carr, 1997). In the analogy of a whip, the handle of the racket must accelerate before the head, thus the head of the racket will be moving faster at contact with the ball. This impact (impulse) is not only the “amount of force used but also the time period that your athlete applies force.” (Carr, 1997).
In combination with properly gripping the racket, utilizing biomechanics techniques for force and velocity, “good technique is characterized by limbs that are slightly flexed at the start of the skill and fully extended from maximal muscular contraction when impact and take-off occur.” (Carr, 1997). Momentum comes largely from arm and leg actions that are transferred at takeoff to the athlete’s body as a whole. (Carr, 1997). Ideally, the force-generation phase utilizes hip and shoulder rotation coupled with full extension of the arm (particularly at impact with the ball). By straightening your arm when you contact the ball, you are able to apply more force. Despite these keys to applying force, “an athlete cannot apply force correctly unless stance and body position are correct.” (Carr, 1997).
“When you watch top-class athletes perform a skill, you get a picture of the speed, rhythm, power, body positions, and other characteristics that make up a quality performance.” (Carr, 1997). In the force-producing phase, shift your body weight from the rear to the forward foot. “Your athlete rotates her hips into the drive and has extended arms when the club contacts the ball.” (Carr, 1997). The most anatomical position to contact the ball is when the ball is between the knee and the hip. The upper arm and elbow of the racket hand stay fairly close to your right side, the elbow bent slightly.” (Johnson & Xanthos, 1997). “As the ball is contacted, the palm of the hand, the wrist, and the forearm move in the direction of the intended shot. The hips, shoulders, and racket move as one unit.” (Carr, 1997). Errors that occur during the force-generation phase “indicate that the athlete is wasting force and not applying it in the correct direction. Inexperience athletes apply force in many different directions.” (Carr, 1997).
As can be seen in the force-generation phase of Venus Williams, (figures 5 and 6), Venus makes use of her early preparation and successful backswing to develop force, power, and technique in performing the forehand stroke. Starting in the low-to-high position (in order to produce topspin), Venus keeps her elbow in toward her side, she pushes the handle of the racket ahead of the head (thus creating a faster velocity), and she successfully transfers her body weight from her rear (right) foot to her front (left) foot. Since Venus hits the ball in the ideal hitting zone and maximizes the forces produced in the ground-reaction force, she has taken advantage of biomechanics.
In contrast to Venus’s stroke, my force-generation phase (figures 5 and 6) does start in a low-to-high arc (an attempt at topspin) but my body position is not in the correct place and therefore, I am not utilizing forces properly. Although it isn’t clearly defined in figures 5 and 6, the head of the racket is moving fast (as indicated because the racket is blurry), but it is not moving as fast as possible because it had not been pushed through with the handle in front of the head. Also, my weight does transfer to my front (left) foot, but because my base is too wide, I do not utilize the forces that will propel the ball. It can be noted that the previous phases (preparatory phase and wind-up phase) have influenced the force-generation phase. In conjunction with working the previous phases, I need to work on my body position during the force generation phase. As indicated by Carr (1997), inexperience athletes apply force in many different directions.” My racket arm is not kept in close to my body and my non-dominant arm is not being utilized as a counterbalance. One good aspect to my stroke is that my shoulders rotate toward a parallel position with the net. This action is one of the reasons that I have been developing a fairly powerful stroke.
The final phase in the forehand stroke is the follow-through/recovery phase. After contact with the ball (in the force generation phase) “your hips and shoulders continue to rotate open toward the net and your racket hand continues to rise.” (Claxton, 1999). “Follow-through and recover actions are those actions that occur immediately after the force-producing motions are complete.” (Carr, 1997). The follow-through is the “continuation of the forward swing through the ball in the direction of the intended target. The follow-through lends continuity to the stroke and fluidity to the whole motion, assuring both power and direction.” (Johnson & Xanthos, 1997). The body weight continues to be predominantly on the forward (left) foot. “The forward knee is bent slightly to help maintain that balance and to facilitate a quick return to the ready position.” (Johnson & Xanthos, 1997). In follow through, the athlete has “applied force and the follow-through safely dissipates the athlete’s momentum and kinetic energy. The momentum generated causes your athlete’s limbs to continue along their original pathway. The follow-through acts to safely dissipate the force of these actions.” (Carr, 1997). One of the main purposes of the recovery phase is to “maintain balance and continuity of motion.” (Carr, 1997).
As can be seen in Venus William’s recovery phase, (professional figures 7 and 8), after contact with the ball, Venus continues the arc from her low-to-high force generation phase through the recovery phase. Venus’s front knee is bent to help maintain balance and thus helps return her to the preparation position.
In contrast, although my recovery phase (figures 7 and 8) is successful in dissipating the forces created through the force generation phase, my racket does not end in the high, shoulder-level height as can be seen in Venus’s professional figures 7 and 8. Additionally, my weight does not transfer to my front foot with the same extreme as Venus. By changing the location in which I hit the ball (ideally in the “hitting zone”, I will be shifting more of my body weight onto my front foot, therefore creating a greater forward motion and more topspin on the ball. Additionally, the racket will end at a higher location as a result of the proper hitting zone. These changes will be the result of optimizing the force, velocity, and power that previously was created in the force generation phase.
In conclusion, it can be seen that the four phases of a forehand stroke (preparatory, wind-up, force generation, and recovery) are interconnected. Each phase influences the next, like a chain reaction. Although my technique was not entirely wrong, I did not perform each fundamental element (weight transfer, elbow in, low-to-high, etc.) to the same extent as Venus Williams. This video analysis was very beneficial to determine how I am applying force and utilizing biomechanics techniques. I have successfully seen how to improve my technique, and by breaking down the forehand stroke into phases, I am able to see individual elements of the stroke to focus on improving.
References:
Carr, G. (1997). Mechanics of sport. Windsor: Human Kinetics.
Claxton, D. (1999). Winning edge series: Tennis. Toronto: WCB McGraw-Hill.
Johnson, J., Xanthos, P. (1997). Tennis (Seventh ed.). New York: WCB McGraw-Hill.
Metzler, M. (2001). Tennis: Mastering the basics with the personalized sports instruction system. Needham Heights, MA: Allyn & Bacon.