COMPONENT 1 - THE LEGS

Positioning of the feet prior and during the serve

As a tennis player approaches the service line, they position their feet in a particular way. Girard, Micallef and Millet (2005, p. 1025) analysed the significance of foot positioning in the lead up to the serve and determined two types that generate different movements; the foot-up platform thrust style (FU) and the foot-back style (FB) (refer to Images 1 and 2).

 

Image 1: Roger Federer uses an FU style of serve, where one leg starts further back and moves forward as he strikes the ball to push off.



Image 2: Maria Sharapova demonstrates more of a FB style during serving, i.e. both legs remain relatively close together throughout the serve.

 

 

Depending on the foot stance the athlete chooses, braking and propulsive impulses can also be observed. Blazvich (I2012, p. 55) identified that when the foot lands at a smaller angle the propulsive impulse is greater, allowing the individual greater ability to accelerate forward. This is identified in the FB style where players can generate greater forward propulsive force and therefore more rapid displacement to the net (Girard, Micallef and Millet, 2005, p. 1025). Dissimilarly, the FU style allows players to develop large vertical forces, however provokes larger horizontal breaking forces, which may hinder performance by provoking slow acceleration to the net. However, a study (Reid, Elliot & Alderson, 2008, p. 312) has shown that the type of stance does not impede serving velocity.

Leg movement during the serve

Newton’s third law of motion states that ‘for every action, there is an equal and opposite reaction’ (Blazvich, 2012, p. 45). This is a fundamental concept observed in the performer’s legs during the serve. With this law in mind, it can be ascertained that applying a large force into the earth will initiate an equal and opposite reaction and propel the player in a particular direction.

Demonstrated in Image 3, is a player applying a force into the ground, followed by his projection upwards and forwards. This specific motion is a reflection of Newton’s third law.  

 

Image 3 - Demonstration of Newton's third law of motion

                                           

But why is a large force important and how do we generate this force?

A larger force that is applied for a longer time (force x time) initiates a greater change in momentum (Blazvich, 2012, p. 53). This is known as the Impulse-momentum relationship, which is observed in the tennis serve in the flexion of the knees for an extended period of time to build momentum. This allows the body to prepare for higher speed movements through a vigorous leg drive (Elliot, 2006).

The leg movements in the tennis serve can be further analysed in terms of a push-like movement pattern, where one end of the kinetic chain is completely free to move (open kinetic movement). A push-like movement extends all joints in our kinetic chain in a single movement and provides a straight line movement that creates greater accuracy (Blazvich, 2012, p. 196).

Dynamic lower limb motion in the tennis serve is vital to a higher speed of the upper torso (Reid, Elliot & Alderson, 2008, p. 311), therefore the way this movement is executed is very significant. Elliot (2006) furthermore suggested that a more forceful leg drive will account for a higher serve velocity.

 

Full leg extension as demonstrated in Image 3, can ultimately assist with accuracy and placement of the ball over the net, by lowering the player’s centre of mass, allowing them to “hang” in the air and therefore reach a greater vertical height (conservation of vertical momentum) (HLPE3531 Workshop handout).