Techniques: Tennis Biomechanics

This section is about the physics of tennis and the biomechanics the sport is based upon. Primarily, what is being said in this article which gets into the scientific application of biomechanics is that the body moves in a particular manner during a throwing motion. This manner is from the closer or primary (proximal) centers of energy to the more distant and secondary (distal) connective links which inturn become centers of energy for the next connecting link. For instance, the shoulder is proximal to the elbow and the elbow is proximal to wrist and so on. So the elbow is distal from the shoulder and the wrist is distal to the elbow and of course the fingers which are called digits, are distal to the wrist. Consequently in an effective throwing motion there is a kinetic link system which enables the body to uncoil from the feet, to the knees, to the hips, to the waist, to the shoulders, to the elbow, to the wrist and complete a release through letting go or imparting spin with the fingers. When a racquet is added there is a final movement which extends the racquet to become the final connective link and is distal to the hand.

In response to questions of biomechanical applications in tennis there is a dynamic and continous activity between players except upon the serve wherein the player is a constant movement from disequilibrium to equilibrium or balance. Getting in this center of relaxed readiness and in place to hit or swing from either side makes tennis an extremely complex game to develop. The additional variable of the racquet and grips plays an integral part in the manner in which the body will address the ball.

In coming articles we will dissect and diagnosis problems and solutions from scientific standards of biomechanical law and physical constraints of motion. There upon the coaches and players involved in this site will see how their feel for the game is backed by physical laws and mechanical principles which are unaltered by coincidental achievements of exceptional talents. In every application there is adjustments which can be made by superior athletes but the strain and complexity of movement will eventually produce injury or errors. Completed full motions following sound biomechanics will induce the opportunity for achievement without underestimating the mental and emotional nature of competition.

The Throwing Motion

Kinetic Link Principle in performance analysis.

Throw like skills are defined scientifically as those in which the primary mechanical purpose is to develop high linear velocity on the end of a segmental link system. These skills may or may not include the use of an implement such as a bat or a racket. If such an implement is used it serves as an additional link in the body's link system.

The specific links used and the motions of each link in the system depend on which skill is being performed. For example, major differences occur in the segmental movements used in performing a golf swing and baseball batting or between overarm throwing and a tennis backhand drive. Slight difference occur in more similar skills, those that belong to a common pattern. Specific skills within the overarm, sidearm, and underarm patterns are slightly different. In the relationship to tennis there are a variety of throwing motions using the full body to impart velocity, spin and direction upon the ball.

Six segments are in a position to be activated during the a throw. They are the pelvis, trunk, shoulder girdle, arm, forearm, and hand. Each has its own movements relative to its own proximal articulation. These articulations are the hip intervertebral, sternoclavicular, shoulder, elbow, radioulnar, and wrist joints. More than one movement could occur in several of these articulations, and exactly which ones are used depends primarily on which specific sport skill is being performed. In this case with tennis we must also include the lower body in the segments and add the knees, ankles and feet working in synchronicity.

Analysis of the throwing motion.

1. The greater the rotational inertia (mass times radius of gyration squared), the smaller the angular acceleration for a given muscle torque.
A. The base segmental torque must accelerate the mass of all the segments distal to its axis of rotation and therefore it must deal with a greater rotational inertia.
B. The distal segmental masses are located farther from the proximal axes of rotation being used, and therefore the radius of gyration for proximal segmental rotations is larger.

2. As the sequences of movements progress to the distal axis, the rotational inertial of the system formed by the remaining rotating segments becomes less.
A. The axis of rotation for each successive distal motion is located farther out on the link system hence it moves closer and closer to the end.
B. The mass of each successive segment is progressive smaller.
C. The radius of gyration for a segment moving in a wheel axle fashion around a longitudinal axis is smaller than that for a lever like movement of the same segment.

Consequently, the link system tends to move faster as the movements proceed to its distal end due to the continual reduction of its rotational inertia. A second variable in the system is the radius of rotation used in calculating the linear velocity of a point on a rotating system. Each axis of rotation is associated with a radius of rotation. The movements of segments distal to the axis of concern increase or decrease the radius of rotation for that axis. For example, the extension of the elbow during the overarm throwing skill increases the radius of rotation relative to the hip axis, the vertebral axis, and the sternoclavicular axis, but does not change the radius of rotation relative to the elbow axis itself.