Introduction to Sports Biomechanics: Analysing Human Movement ...

INTRODUCTION TO SPORTS BIOMECHANICS
These ‘movement analysis supplements’ are particularly relevant when we ask the question
that kept arising in the section on ‘Fundamental movements’ in Chapter 1, ‘How
are these movements coordinated to produce the desired outcome?’ They may be
described, for now, as computer-generated animation sequences and graphs.
Computer-generated animation sequences are simplified representations of video
movement sequences and are obtained from them. The degree of ‘abstraction’ can
run from ‘skeletal’ stick figures (Figure 3.1) to ‘solid body’ representations (such as
that of Figure 3.2) to ones that can have almost as much detail as the video sequence
itself.
Graphs can be of several types, of which the most useful for the movement analyst
are time series, angle–angle diagrams and phase planes. Time series are simply graphs
(or plots), of one movement variable, such as joint angle, as it changes over time during
the course of the movement. Several time series can be plotted on the same graph.
Angle–angle diagrams are graphs of one joint angle as a function of another. The focus
is how one angle changes with changes in a second angle; in other words we focus on
how the two angles ‘co-vary’ rather than how they each evolve with time. Angle–angle
diagrams are used extensively in the study of movement coordination. Phase planes are
normally graphs of the angular velocity of one joint as a function of the angle of that
same joint. The focus is on the so-called ‘coordination dynamics’ of that joint. Phase
planes are also used extensively in the study of movement coordination. All three of
these graphs will be discussed in detail in the following sections.
Figure 3.2 Solid body model of cricket fast bowler.
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