Sequential Body Segment Rotation During Serve example essay topic

Positions for observation Most used for observation of the serve was the side camera view because the angle was best for analysing weight transfer throughout the serving action. For example, the rock and the follow through. The side on view to direction of travel is also best to examine the full travel of the body segments as movement was in a forward motion. The Back view was used for the ball toss and again the follow through. Viewing from the back showed the amount the angle was off a vertical line that the tennis ball obtained during the ball toss.

The front view was used for stance and follow through which is the weight transfer forward throughout the serve, it showed the changes in body positioning throughout the entire serve. By zooming in and seeing the tape on the areas of rotation and movement we could see more detailed joint movements. (For example, elbow bending in back swing). Whole body movements were displayed by zooming out and surveying the whole subject (e.g. follow through). Lighting Videotaping was outside in fairly bright sunlight because good light was needed to highlight the subject.

If natural lighting was insufficient then artificial lighting would have to be used (e.g. spotlights). Our observations had to be seen facing away from the sun to avoid glare. Background The background contained a building and other small objects such as a fence and some plants. The ball toss was shown against a light post in the background and enabled us to gauge how straight the ball toss was thrown and allowed comparison to a vertical landmark. The background during the serve was a grey colour so the yellow tennis ball and the subject stood out against the background. Shutter Speed The camera was on the fastest shutter speed to allow minimal light entry because of the bright sunlight and maximum viewing of the steps of the serve.

It also needed to be a faster shutter speed to stop blurring of the subject and enhance the finer details. This enabled us to slow down the serving action for more precise scrutiny. Subject Preparation White tape against dark clothing was used on the subject's joints (e.g. elbow, knee, leg) to track movements throughout the serving action and to be able to see the movements in finer detail. Biomechanical Principles The serve is affected by the following: Mass / Weight This is constant during the serve. A greater mass will contribute to a greater force during the serve. (ie, F = ma) Friction Used by the feet against the court surface to hold position during the serve in order to avoid slipping or stepping over the base line, thus incurring a foot fault. (maybe something on the spin of the ball... like contact between the strings and the ball) I dunno!!?!?! Centre of Gravity (CoG) originated around the navel area of the server, moves upwards during the ball toss, then moves back down after contact is made with the ball by the racquet.

During the follow through, CoG is located outside of the body. Positioning and height of the CoG are contributing factors to a stable equilibrium. (Rowan University, n. d.) Base of Support is constant and balanced, and accommodates push off, but stops falling. (Rowan University, n. d.) Angular motion (angular momentum) produced via racquet and trunk rotation. This depends on the torque acting and the time over which it acts. In the case of the serve is increased by increasing the force applied.

Trunk and upper chest of server rotate in one direction, producing opposite and equal rotation of pelvic girdle and lower body. (Newtons 3rd Law) (Rowan University, n. d.) Effectiveness of torque produced by muscles around a joint is centred around the radio ulnar joint; 21% of the serves total kinetic energy is produced by this joint, with an angular velocity of over 300 degrees per second. (Rowan University, n. d.) Open Kinetic Chain where the most distal segment in the movement (ie. Hand holding racquet) is free to move in space. Sequential body segment rotation during serve produces the desired high level of angular velocity. Accuracy of ball placement (the other main objective of the tennis serve along with velocity is assisted via positioning of the racquet face through pronation of the forearm.

(Rowan University, n. d) Reference - Rowan University (n. d.) Tennis Serve Biomechanics. Retrieved April 9, 2003, web Biomechanical principles applicable to a tennis serve (again) Newtons 2nd law of Motion (Acceleration) "the change in motion of an object is proportional to the force impressed; and is made in the direction of the straight line in which it is impressed". This law is demonstrated at the peak of the ball toss; the ball is heading straight up after being released by the player, at a relatively slow speed. At the height of the ball toss, the ball experiences rapid acceleration away from the player via the force impressed upon it by the racquet, in a straight line from the direction that the racquet makes contact with the ball. Thus, the greater the force impressed by the strings of the racquet, the quicker the serve will be. Impulse (aka Change in Momentum) I = ft Impulse is the product of force and time, and again is demonstrated where the racquet makes contact with the ball.

It is not possible to increase the time that force is applied (in order to increase the impulse) As the time period is constrained, so the other option is to increase the force over the constrained time period. Thus, the more force that is applied over this shorter time period, the quicker the serve will be. Coefficient of Restitution the ability of a body to return to its original shape once deformed, which differs from body to body. This principle ties into the tennis serve with the string tension of the racquet, a properly strung racquet will provide the correct amount of tension for acceleration of the ball, as both the ball and racquet deform slightly, and then return to their former shape.

Open Kinetic Chain where the most distal segment in the movement (ie. The hand holding the racquet) is free to move in space. Qualitative Analysis of the Performance In terms of the critical features, this performance was very much less than perfect. Obviously the performance could not be perfect, because otherwise there would be nothing to improve.

The various angles and filming techniques allowed us to detect the faults and weaknesses of the serve. When looking at the subjects feet on the video, you can see that the position of the feet and the stance taken at the beginning if the serve is correct. However during most of the serves recorded, there has been continuous foot faulting by the subject. The feet are also in the wrong position when they are brought together and the ball is hit. The movement of the subjects body during the serve is one of the main faults in the action.

The subject begins with her weight on her front foot with her back slightly bent, which is correct. However as she begins to take her racquet back and her ball toss arm upwards, her body is too upright, this means that the force that could have been generated was not. Once the subject hits the ball, she doesn't move in a flowing motion. This is a combination of her body being too upright and bad timing with striking the ball. This too means that the force generated will not be as intense, the accuracy may also be affected. During the first phase of the action, the subjects elbow is meant to be higher then her shoulder, reaching down her back.

This critical feature is achieved, but not with consistency. Not bending the elbow enough will mean less time to increase velocity in the swing. It can also leave the player off balance, and can lead to striking the ball in the wrong position or at the wrong time. The ball toss is a very important part if a tennis serve. The angle, height and spin on the ball can all determine the success of the serve. This is another major weakness in the subjects serve observed.

The general height of the ball toss is at a good level, the spin on the ball could be slightly improved, but the major fault is the angle that the ball is thrown at. It is inconsistent and often too out in front or too far to the right. This will effect the accuracy of the serve as the player may have to reposition to hit the ball. The velocity of the serve may also be negatively affected. The follow through in the tennis serve is another key part in producing a successful, accurate serve. If the player fails to follow through it will mean that the ball will not go exactly where you want it to go.

The force of the serve may also be affected if the action is stopped short. By analysing the performance it was clear to see that the follow through of the subject was correct, as the servers racquet and arm finished on the correct side of the body, and the motion was properly completed in a smooth motion..