DYNAMIC BALANCE
Maintaining good balance before, during and after the strokes is one of the most important aspects for producing successful stroke. The stroke mechanics usually breaks down if the player can’t maintain the state of dynamic balance (phase of loading + following through + stability of the deceleration to begin the recovery). Player in balanced position can have more chance to have technically efficient movement of the racquet through the ball which can affect the tactical aspect (efficient decision making) and technical aspect (stroke execution to support that decision) of the stroke.
Balance is an ability to maintain the line of gravity (vertical line from the center of mass to the ground) within the base of support with minimal postural sway. How the line of gravity and base of support work together while the player is moving (or initiating movement), will determine the ability of maintaining balance or decelerating efficiently to loading.
Successful movement in tennis depends of keeping the line of gravity as closer to the center of the base of support as possible. But at the same time, the line of gravity can enable player to accelerate. If the line of gravity moves towards the boundaries of the base of support, it enables the player to accelerate forwards, backwards or lateral. The imbalance created at this moment, makes the players move their feet to prevent themselves from falling while not slowing down the movement. The push off leg swings ahead preventing the body from falling but pushing off at the same time leg for the next stride to the desired direction. When accelerating, allowing the body center of mass to move over the base of support, by pulling the foot towards the middle or supinating the foot while landing from the split step, is making base of support smaller which enables the forces of gravity to provide us with the acceleration (falling motion) instead of initiating the movement by the muscle forces.
CONCLUSION: Lack of balance causes the player to change the tactical purpose of the stroke as the potential offensive stroke (through efficient coordination of the body segments) has to be adjusted because the speed and range of motion are limited. This drastically affects the tactical effect of the stroke and puts the player into neutral or defensive situation choosing stability in the stroke rather then fluid acceleration.
BASE OF STABILITY at a LOADING stage
Loading in tennis refers to the balanced coiling of the upper and lower body muscle groups away from the incoming ball direction (retraction phase). This is done in order to timely uncoil the same muscle groups in the chain of segmental motions through the ball (action phase) towards the targeted direction.
Balanced and timely loading usually begins from the ground up around the stable loading foot.
Putting the weight coiling pressure to the loading foot against the ground, the knee and hip joints are moving the line of gravity towards the loading foot creating a wide and stable base of support lowering the player’s center of gravity. By doing that a player receives much needed stability to perform a movement forward with much acceleration.
CONCLUSION For a player to move the body segments efficiently, there should be optimum combination of the stability and mobility through lowering the center of gravity created by loading the major muscle groups of the lower extremities.
In order to produce longer efficient range of motion of the stroke from the moment of dropping the top of the racquet to the moment of extending the hitting arm forwards, the loading foot need to transfer the energy from the ground to the hip by pushing him off towards the contact point.
CONCLUSION Loading foot position (the inner part of the foot vs toes directing to the ball) can determine the level of force production by the player. Pivoting the foot enables more efficient loading of the lower body muscle groups delivering larger amounts of force production from the ground up to the upper body. Limited pivoting of the loading foot pressures player to create driving forces mostly from the upper body.
TRUNK (SHOULDER and HIP) MECHANICS
The upper body rotation usually includes the shoulder rotation, pulling away the hitting shoulder away from the front hip (see the blog about serape). For the sake of efficiency, the player has to have a strong planted foot against the ground, hip coiled to some degree and at this point the shoulders can be enabled to efficiently rotate further then hips (shoulders should always have the separation angle of rotation larger then the hips in the loading position) which increases the amount of energy transferred from the legs and gluteus. To increase the distance and elastic recoil, shoulders should rotate between 90 and 120 degrees passed the baseline at the backswing to add more elastic energy to the muscles of the trunk. The reason the players create a larger upper trunk rotation beyond the hips is to pre stretch the trunk rotator muscles and create a powerful separation angle.
The separation angle on average at the forehand stroke is at 20 degrees but at the one handed backhand even 30 degrees which states that the players with one handed backhand need more timely planting foot stability to enable further shoulder rotation. (Data taken from Tennis Medicine: A Complete Guide to Evaluation, Treatment, and Rehabilitation; edited by Giovanni Di Giacomo, Todd S. Ellenbecker, W. Ben Kibler, 2018).
As the speed of trunk rotation is correlated with the racquet velocity, uncoiling of the trunk through the ball will enable the flowing acceleration. After the initial coil of the hips, shoulder rotation creates a larger separation angle to add more elastic energy into the upper torso. From the leg drive the torso is pushed forward explosively to the ball creating a late arm leg.
By adjusting the combination of the timing of the shoulder rotation and amount of trunk rotation, the players can determine the angle of the racquet meeting the ball at the contact point which determines the direction of the future stroke. It was shown that elite and high performance players create greater hip alignment rotations but smaller separation angles when playing forehand strokes at the comfortable height down the line compared to cross court.
CONCLUSION Upper body force creation depends of the elastic capabilities of the muscles of the trunk but mostly of the timely reaction in order for the player to enable the optimal shoulder rotation angle compared to hips (separation angle). As mentioned, the separation angle of the forehand, one handed and two handed backhand varies but it’s always present as the force creating prerequisite. Registering and identifying the opponent’s movement of the shoulders and to which degree the shoulder rotation can contribute to the generation of the force, can provide the cues to the player about the intention of the opponent’s stroke.
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