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BIOMECHANICS

Biomechanics is the study of the effect of forces on the body. Just two examples of such forces include the Earth’s gravity and the muscles’ own elasticity. By obtaining an understanding of the biomechanics involved in each tennis stroke, coaches are able to direct athletes to use their muscles in the most efficient and injury-free ways.

[Technique Development]
[Segmental Interaction]
[Elastic Energy]
[Dissection of Specific Strokes]
[Junior Racquets]

TECHNIQUE DEVELOPMENT

Traditionally, all tennis players were taught to execute their strokes in a certain way. This was meant to reduce injury. A tennis player would stand in a way that would allow him or her to “step into the ball”. This is done by placing the foot opposite to the dominant hand slightly in front. As the tennis player hits the ball and steps forward, energy is transferred from the back foot forward to the ball. Although traditional technique appears to be energy efficient, contemporary coaches criticize that this motion is too mechanical. In fact, a close observation of top ranked international tennis players reveals that their technique does not follow traditional technique. Instead of turning to traditional technique, tennis players rely more upon their intuitivism. Tennis players’ techniques are usually based upon past experience, world trends and fluency. (Hughes et al., 1995)

  1. Past experience- An example would be that some tennis players choose to use the western grip to hold their tennis racquet, where the palm of the hand is placed more parallel to the net than the traditional “hand-shake grip”. This is because they have noticed that gripping the racquet in this fashion will allow them to implement more topspin by brushing the top of the ball on the follow-through. A ball with a lot of topspin is harder for the opponent to return because it the ball hits the ground faster and rebounds at a sharper angle.
  2. World trends- Most international tennis players use the open stance position, where one foot is not placed forward. This may influence younger tennis players to follow this trend.
  3. Individual feeling of fluency- To a tennis player who consistently plays in a competitive atmosphere, the most important deciding factor is to be able to “go with the flow” of the rally.

SEGMENTAL INTERACTION

Segmental interaction is the transfer of energy from large to smaller joints of the body. This is how tennis players efficiently transfer energy through different parts of their body to the ball, without disrupting the fluency of their technique. For example, the energy may originate from deeply bent knees of a tennis player. In preparation of hitting the ball, the tennis player also rotates their body. This creates a build-up of elastic energy in the torso. As the racquet is swung forward, the energy from the large leg and torso joints is transferred to the smaller upper arm muscles, elbow joint and wrist joint, and to the ball as kinetic energy.

ELASTIC ENERGY

Competitive league tennis players require an immense amount of energy to counter the balls hit by their elite opponents. In order to complete this, the tennis players need to efficiently transfer their energy. This efficient transfer of energy is possible through the use of elastic energy. When tennis players prepare to hit a ball, they will point their entire arm almost perpendicular to the back of the court. This is known as their backswing. In doing so, the arm muscles of a tennis player will stretch similar to a stretched elastic band. At this phase in the player’s technique, there is much elastic energy stored in the arm muscles. As the tennis player swings their racquet to contact the ball at a point close to their body, the arm muscles rebound to their original form (figure 5). During this rebound, an immense amount of energy is released to assist the tennis player in returning the ball over the net. However, if a tennis player initiates their backswing too soon, the effect of the elastic energy will lack efficiency. The stored elastic energy will quickly disappear as the muscles strive to return to their original form. In fact, there is already a 55% loss of the energy in 1 second. By the time that 4 seconds have passed, 100% of the energy will be lost. Therefore, in order to maximize efficiency, a tennis player needs to maintain a high level of fluency in their technique in the transfer of energy. There would need to be minimum time between the phases. This is especially crucial to the performance of junior tennis players, as they have little muscle strength to overcome the inertia of the racquet. (Hughes et al., 1995)

Muscular Elastic Energy (originally-created graphic)
Figure 5; Muscular Elastic Energy
During the backswing of a stroke, a tennis player will stretch their muscles. The resulting effect is much similar to stretching an elastic. There is much elastic energy stored in the muscles. As the arm muscles rebound to their original form, they relase an immense amount of energy that contributes to the power that the tennis players exerts onto the ball.

Leg muscles also use elastic energy to assist the player. An excellent exemplar is in the technique that Andy Roddick exhibits. During Roddick’s follow-through, his muscles are elongated to a point where they are slightly stretched. This stretch is, again, similar to the stretching of the elastic band. The stretched muscles, then, possess stored elastic energy. The elastic energy increases the muscles’ tendency to rebound quicker. This is comparable to a slingshot. The more the elastic is stretched back, the higher the tendency that the elastic has to rebound to its original shape. Therefore, Roddick’s leg muscles’ contraction, due to their high tendency to rebound, allows him to return to his ready position of a deep knee-bend quicker. Furthermore, the immense energy from the rebound of the muscles will naturally make Roddick have his centre-of-gravity lower to the ground. This is very efficient technique, as his low centre-of-gravity allows him to possess greater balance. In addition, the low centre-of-gravity allows him more time to store energy to transfer to the ball, when he will explosively extend his legs from his deep knee bend.

DISSECTION OF SPECIFIC TENNIS STROKES

The following includes a dissection of the four most commonly used strokes in tennis: the forehand, the backhand, the serve and the volley.

Forehand- hitting the ball with the palm of your dominant hand facing the court at about hip to shoulder level

  • Backswing- An elite player’s shoulders are rotated about 100° from their ready position of facing parallel to the net. This stretch in the player’s arm muscles stores a large amount of elastic energy to assist the player. The movement of the player’s arm from ready position can be straight, looped or hinged at the elbow, depending on the player’s feeling of fluency.
  • Transfer of energy- A player may choose to use traditional or contemporary technique. Lower body motion is responsible for 10% of the racquet velocity in the transfer of energy.
    • Traditional- The foot on the side of the non-dominant hand is slightly in front. The player “steps into the ball”.
    • Contemporary- The player stands in an open stance, where there is not a foot stepped forward. There is much trunk rotation during the transfer of energy.
  • Point of Contact- Shoulders are approximately 95° from the backswing position. Elite players may use multi-segment motion. Multi-segment motion is where each part of the arm is enabled to move individually rather than one straight apparatus. There is usually an increase in racquet velocity with the use of multi-segment motion. The average increase in racquet velocity when implementing multi-segment motion is 2.2m/s. Players who use multi-segment motion will also be able to be able to hit a larger variety of trajectories.

Backhand- hitting the ball with the palm of your hand facing yourself usually at hip to shoulder level

  • Backswing- The shoulders rotate approximately 124° from the ready position. This stretching in the player’s arm muscles stores a large amount of elastic energy to assist the player.
  • Transfer of energy- Among elites, rotation of the elbow is used to increase the velocity of the racquet. However, research reveals that the maximum velocity of the racquet occurs at an average of 0.08 seconds before contact. Therefore, it can be concluded that this technique may not be meant for efficient energy use, but for comfortable fluency. In addition, there is rapid trunk and torso rotation.
  • Point of contact- The trajectory of the ball depends upon the height of contact and the amount of spin that the player plans to apply. Spin is implemented upon the ball through a brushing motion on the ball.
  • Two-handed backhand- Some players choose to place both hands on the racquet when hitting a backhand. The non-dominant hand directs and applies most of the power to the racquet. The dominant hand stabilizes the racquet during this process. The two-handed backhand is chiefly accepted by coaches, as it is generally more powerful than the one-handed backhand and does not require players to adjust their grip as the one-handed backhand does. These reasons are especially justified by the immense power and speed of modern tennis. In regards to speed, the two-handed backhand is especially useful on the fast court surfaces of grass and asphalt. Because the two-handed backhand is much more powerful than the one-handed backhand, it only requires compact backswings, making it more practical on fast court surfaces. The compact nature of the two-handed backhand’s backswing is also the reason why it is common for players to return lightning quick serves with the two-handed backhand. The compact swing allows greater control, stability and aggressiveness. The compact quality also allows players to disguise their strokes. Players do this by taking advantage of the lesser amount of time it takes to prepare for this type of shot and hitting the ball as late as possible.

Service- hitting the ball at a point over your head in a diagonal direction

  • Stance- If the back foot is too close to the front foot, the player may lose stability. This is because of a smaller base for support. A deep knee bend maximizes generation and transfer of power.
  • Backswing- The elbow is bent upward into a “back-scratch” position. This stretches the triceps and shoulder muscles. The stretch of these muscles produces stored elastic energy in these muscles to assist the player in gaining more power in their serve. The trunk and hips are rotated at an identical angle.
  • Ball toss- There is apparently no optimal height for the ball toss. However, according to the laboratory report, “Analysis of tennis serves of National and County players,” the ball toss should be higher than the optimal point of impact, which is 1.4-1.5 times the player’s standing height.
  • Point of contact- The point of impact is usually 1.4-1.5 times the player’s standing height. Professional players contact the ball at an even higher height. This is due to their greater leg drive. A higher point of contact is also attributed to an increased thigh to trunk angle. The knee joint is extended. There is increased hip rotation that is proportional to the height that the player lifts off of the ground. The arm is angled toward into the court. The body should continue its natural movement to reduce physical stress.

Volley- blocking the ball from the air before it bounces on your court

  • Backswing- The amount of backswing increases as a player is farther away from the net. This is simply for the reason that an increase in backswing is needed to return the ball at a slightly longer distance. For example, the backswing closer to the net would be near the shoulder or be directly in front of the shoulder. A backhand volley backswing near the net may be slightly farther back. At about the middle of the court, the backswing should be placed behind the shoulder. Once again, the backhand volley backswing from this point in the court may also be slightly farther back.
  • Point of contact- The player pushes the ball in the direction that they would like the ball to land on their opponent’s court. The player moves their arm in a forward and downward motion. Professional tennis players’ wrists usually have a sudden increase in velocity in the process of directing the ball.

JUNIOR RACQUETS

As children just begin to play tennis, coaches need to ensure that the tennis racquet is not too big for pupils. Numerous studies have done by scientists in regards to the impact of the size of racquet on young junior tennis players. It was concluded in these studies that a junior tennis player would definitely benefit from the utilization of a smaller racquet. With smaller tennis racquets, subject junior tennis players were able to hit the ball at a greater velocity and keep the racquet more vertical during impact of the ball. With the usage of smaller racquets, there was an evident increase of consistency in service, forehands and backhands. The only stroke that increased in consistency amongst players with a larger racquet was the volley. Combining two of Newton’s laws of motion, we know that a greater mass at rest will possess more inertia because it will resist movement at a greater extent than a smaller mass. The reason why the larger racquets were not as useful to the junior players was because its greater mass increased the amount of inertia that a player would have to overcome when swinging the racquet forward from a period of no movement. At such a young age when children typically have not developed large muscular capacity, this excessive inertia would unquestionably impede their performance. However, the effectiveness of the larger racquets in executing volleys can be explained by the lesser swing of the racquet.

Copyright © 2005 Iris Wong, Grade 11, Queen Elizabeth High School, Calgary, Alberta
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