Acceleration

 

Throughout the acceleration stage the shoulder joint plays an important role of internal rotation in the upper arm. The internal rotator musculature must accelerate the upper arm in the swing to impact before the external rotators contract to decelerate this rotation during the follow through phase of the action (Escamilla & Andrews, 2009).

To increase the velocity of the ball in the serve there are multiple biomechanical principals that can be utilised. One of them being angular velocity, which is an objects rotational velocity about an axis. This biomechanical principle is useful in understanding how to increase serve velocity as measuring the angular velocity as the greater the objects angular velocity, the faster it will move around its axis. When examining angular velocity in a tennis serve, we will specifically be looking at the athletes shoulder rotation in the acceleration phase before contact. Angular velocity can be calculated following the below equation.

Equation of angular velocity:

 

In a study, Escamilla & Andrews (2009), found during the acceleration phase, the Pectoralis major, latissimus dorsi and subscapularis activity was greatest, as they contract to help generate a peak shoulder internal rotation angular velocity approximately 2500°/sec.

The video displays the analysis of the angular velocity of the shoulder during the acceleration stage

This video examines the angular velocity of the acceleration stage.

Cocking stage starts at- 55.6° at 1.20 seconds and finishes at 170.4° at 1.36 seconds.

Therefore:

Δθ=θ2 −θ1 =170.4°− 55.6°=114.8°

 

Δt=t2 −t1 =1.36 sec−1.20 sec=0.16 sec

 

 = 114.8°/ 0.16 seconds = 717.5°/sec

Figure 3: start of acceleration (cocking stage)

Figure 4: End of acceleration stage 

Furthermore, the racket design is a notable component of the serve. It has been said that racket design is formulated to increase torque as the athletes shoulder rotates throughout the serve.  Traditionally racks made out of wood had a mass size of 400 grams, where as today, rackets made from graphite have a mass of 250 grams, hence are almost has of the mass of wooden rackets. The decrease in mass means the moment of inertia is reduced as the arm rotates around the shoulder, consequently creating greater torque. The greater torque then results in greater angular momentum.

Equation for torque:

Torque= force x distance

Momentum, denoted as p, represents the motion quantity of a moving object, calculated by multiplying its mass (m) and velocity (v). Consequently, as depicted in the following equations, a racket with less weight acquires lower momentum.

​p = mv

 

p= 0.25kg x 10m/s

p= 2.5kg m/s

 

p= 0.2kg x 10m/s

p= 2kg m/s

 

Therefore, increasing the bass of the racket can potentially decrease angular velocity.  

Moreover, there are serval other biomechanical principles that can help increase a players velocity in the serve. One being increasing the radius of gyration of muscle mass nearer to the shoulders. This is beneficial as particles located at a further away from the rotational axis exert a larger impact on the moment of inertia. Therefore, the athlete can increase their angular velocity by developing and strengthening the muscles around the shoulders.

Injury prevention

It is essential to design specialized training routines to protect the shoulder from potential injuries. The velocity produced by specific joints may exert excessive strain on the surrounding tissue around the joint, potentially resulting in acute or chronic injuries. Additionally, t is important that each tennis athlete has a structured core/lower back injury prevention program in place to offset these rather unusual body movements (Kovacs & Ellenbecker, 2011).