Introduction to Sports Biomechanics: Analysing Human Movement ...

INTRODUCTION TO SPORTS BIOMECHANICS
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INTRODUCTION
In Chapter 4, we covered quantitative videography of sports movements. In the final
two chapters of this book, we will explore how these movements are generated. In this
chapter, we will consider the forces that affect the movement of the sports performer.
This branch of knowledge is often called ‘kinetics’, and is subdivided into linear and
angular (rotational) kinetics; it deals with the action of forces and torques in producing
or changing motion. We will also look at how we measure the forces and pressures
acting on the sports performer.
BOX 5.1 LEARNING OUTCOMES
After reading this chapter you should be able to:
appreciate how and why the variation with time of the forces acting on a sports performer
can be viewed as another movement pattern that can be evaluated both qualitatively and
quantitatively
define force and identify the external forces acting in sport and how they affect movement
understand the laws of linear kinetics and related concepts such as linear momentum
calculate, from segmental and kinematic data, the position of the centre of mass of the
human performer
identify the ways in which rotation is acquired and controlled in sports movements
understand the laws of angular kinetics and related concepts such as angular momentum
appreciate why the measurement of the external forces acting on the sports performer is
important in analysing sports movements
understand the characteristics of a force plate that affect the accuracy of force measurement
outline the procedures to be used when measuring force and pressure
evaluate the information that can be obtained from force and pressure measurements.
FORCES IN SPORT
A force can be considered as the pushing or pulling action that one object exerts on
another. Forces are vectors; they possess both a magnitude and a directional quality. The
latter is specified by the direction in which the force acts and by the point on an object
at which the force acts – its point of application. Alternatively, the total directional
quality of the force can be given by its line of action, as in Figure 5.1.
The effects of a force are not altered by moving it along its line of action. Its effects
on rotation – though not on linear motion – are changed if the force is moved parallel
to the original direction and away from its line of action. A torque, also known as a