Principles of EFFICIENT MOVEMENT and PERFORMANCE
Maintaining good balance before, during and after the strokes is one of the most important aspects for producing a 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). The 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 the 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 centre 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 to maintain balance or decelerating efficiently to loading.
BASE OF STABILITY at a LOADING stage
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 move forward with much acceleration.
For a player to move the body segments efficiently, there should be an 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 a longer efficient range of motion of the stroke from the moment of the racquet drop 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 off towards the contact point.
TRUNK (SHOULDER and HIP) MECHANICS
Upper body force creation depends on the elastic capabilities of the muscles of the trunk. The upper body rotation usually includes the shoulder rotation, pulling away from the hitting shoulder away from the front hip. 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.
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.
How MOVEMENT influences the STROKES
Movement skills include the reaction time, efficiency of perception, body reaction speed, speed of movement and efficiency of adjustments to the ball. About 70% of occurring errors in the game (by official statistics) is because of the poor timing and technique of the movement, not because of stroke mechanics.
The analysis of the movement pattern has two elements:
1. Firstly, understanding the way the player is initiating a movement to the ball. Based on the information about reaction and the initiating step, players can predict the reaction of the opponent towards the ball. Elite tennis movers react while still being in the split step above the ground and then initiate their movement by landing only with the foot further of the direction of the movement to enable the quickstep to the opposite way from landing.
2. Secondly, analyzing how the last step before the stroke initiation can influence the movement of the player through the ball. Identifying if the last step is enabling player to keep the wide and stable base of support gives information about the possibility of the stroke to be more or less effective and aggressive. By that means, if the player is able to create the timely linear momentum or not.
BIOMECHANICS and ENERGY of the STROKES
In tennis, the player transfers the energy from the body to the ball through a tennis racket generating speed and spin of the ball. Energy can be potential (stored energy) or kinetic energy (the energy of movement).
Potential energy is elastic energy stored in muscles and tendons under tension. Muscles in human body function in the same way as shooting a rubber band. The tension developed in the junction of the muscles and their tendons by the eccentric loading, causes them to act in a rubber band manner. When the stretch shortening cycle occurs this kind of elastic stretching (eccentric muscular contraction), is immediately followed by an explosive concentric muscular contraction (the release).
The stretch–reflex is an involuntary reflex and it causes the stretched muscle to contract stronger and at the same time inhibits the antagonist muscle from contracting (if they do they are slowing the movement). The rate of contraction is significantly faster and more powerful than in condition of the voluntary muscular contraction as the faster the muscle is stretched eccentrically, the greater the force will be on the following concentric contraction.
The importance of the flowing energy through the chain of motion (from the potential to the kinetic) is not related only to the efficiency of performing a stroke in tennis but for the movement as well. Rapid transfer of energy while keeping the balance is the prerequisite for the efficient reaction and movement to the ball. Every human motion involves the coordinated and synchronized movement about many joints working together and although every segment of the body can be identified as an individual motion generation part, in order for humans to perform all this parts need to work together in a chain. The breakage of the energy flow at the kinetic chain can be for several reasons among which the most common is poor stroke mechanics due to the poor preparation timing.