Introduction to Sports Biomechanics: Analysing Human Movement ...

movement patterns, coordination diagrams such as angle–angle diagrams (Figures 3.13
and 3.14) or phase planes (Figure 3.20) can also be obtained; quantitative analysts often
want to quantify such graphs, in contrast to the qualitative analyst, whose focus will be
on their shape (topography).
Quantitative analysts may also identify values of some variables at important instants
in the movement to allow inter- or intra-performer comparisons. These values, often
called performance parameters or variables, are usually defined at the key events that
separate the phases of sports movements, such as foot strike in running, release of a
discus or bar release in gymnastics. They are discrete measures that, although they can
be very important for that performer, discard the richness of movement information
contained in time-series graphs or coordination diagrams.
Computer visualisation of the movement will also be possible. This can be in the
form of stick figure sequences, such as Figures 3.1 and 3.2. These are quick and easy to
produce but have ambiguities with respect to whether limbs are in front of or behind
the body (Figure 4.1(a)). In three-dimensional analysis, this can be partially overcome
by filling in the body and using hidden line removal (Figure 4.1(b)). Full solid-body
modelling (Figure 3.2) is even more effective in this respect, but computationally
somewhat time-consuming. Solid-body models can also be made more realistic through
the use of shading and surface rendering.
Calculating forces and torques (inverse dynamics)
QUANTITATIVE ANALYSIS OF MOVEMENT
Figure 4.1 Computer visualisation: (a) stick figure of hammer thrower; (b) as (a) but with body shading and hidden line
removal.
In the previous subsection, we considered ‘kinematic’ variables, specifically joint
angles, angular velocities and angular accelerations. Quantitative analysts also study
the ‘kinetics’ of the movement – forces, torques, and so on. This often involves the
calculation of kinetic variables for joints and body segments to try to understand
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