Apart from being one of the most important strokes in the
game, the tennis serve is also the most complex (Girard et al., 2005). It is unique to the game as it is the only
stroke in which the player has complete control over, as it is not interfered
with by their opponent. There are three main types of tennis serves; the flat
serve, the slice serve and the kick serve. However, despite these slight
variations, all three types of serves are extremely similar in the biomechanical
principles behind them.
BIOMECHANICS BLOG
The tennis serve is the only stroke in the game of tennis that a player has complete control over. What must this player do in order to maximise power, while still achieving accuracy?
Monday, 22 April 2013
Kinetic Chain:
Figure 1. The movement
pattern of an elite tennis server (Image credit: Roetert et al.)
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The kinetic chain is a series of linked segments of a body
that move together (Blazevich, 2010). Two different forms of this chain include
the push-like pattern and the throw-like pattern. At an elite level, the tennis
serve is accomplished using the throw-like pattern, meaning that it is a
sequential movement pattern starting at the feet, moving up through the trunk,
and all the way out through the hand and racquet. According to Kibler (2009), 51%
of kinetic energy is produced by the trunk and legs, 13% by the shoulder, 21%
by the elbow and 15% by the wrist.
The tennis serve can be broken down into three phases;
preparation, acceleration and the follow-through. In the preparation phase,
which includes the ball toss and ends at the full shoulder external rotation, potential
energy is stored to be used as kinetic energy in the acceleration phase (Kovacs
& Ellenbecker, 2011). A great deal
of energy is obtained through the flexion of the knee (shown in images B-C in Figure 1) as it produces a ground-reaction force (Roetert et
al, 2009). This means that the ground gives off an opposite force to
that of the downward force being placed on it by the foot, relevant to Newton’s
third law of motion. In Figure 1 (images C-E) we can also see a hip and trunk rotation, which is the next
sequential part of the kinetic chain.
The acceleration phase begins as the kinetic energy moves up
into the shoulder and arm due to the hip and trunk rotation (Kovacs & Ellenbecker,
2011). At this stage of the movement
pattern, the shoulder has rotated so the elbow has undergone flexion behind the
back, as can be seen in Figure 2. The
arm then starts to generate torque as it is swung back around to make contact
with the ball. The ball is contacted when the elbow is almost at maximum
extension, with the forearm facing toward the ground. This internal shoulder
rotation movement is evident in images D-F
in Figure 1, which is a large
contributor to the high speed of the racquet head at the point at which contact
is made with the ball (Roetert et al, 2009).
Figure 2. The
acceleration phase of the tennis serve (Image credit: Abrams et al.)
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The last phase of the movement pattern is the follow
through. During this phase, the body undergoes deceleration and finishing the
shot in order to prepare themselves to play the next shot returned by their
opponent. This aspect of the serve is the most violent on the body, where internal
shoulder rotation and forearm pronation continues right through past the trunk
in order to ensure the ball is going in the right direction (Kovacs &
Ellenbecker, 2011). It is here where the muscles around the shoulder and arm
begin to decelerate. The abdomen’s internal oblique muscle, on the side of the
players opposing hand, is very active in this part of the shot, as it has to
maintain stability in the trunk and help pull it back from an unbalanced position
back to a balanced one (Kovacs & Ellenbecker, 2011).
The last part of the movement pattern is where the lower
body lands back on the ground. When the front foot contacts the ground it
creates eccentric and horizontal braking forces to stabilise the body (Bahamonde & Knudson,
2001). Due to the players momentum behind the ball and sudden stopping,
the player will lean right forward and over the front foot creating a shift in
the centre of mass (Bahamonde & Knudson, 2001). To counteract this, the back leg
is kicked out behind to maintain balance, which can be seen in both image F in Figure
1, and more clearly in Figure 3 below.
This allows the player to then come back together in the upright position
without falling over, and get ready to return the next shot.
Figure 3. The athlete
stabilising his body using horizontal breaking forces in his front leg, and
swinging his back leg behind to maintain balance. (Image credit: Kovacs &
Ellenbecker)
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