Introduction to Sports Biomechanics: Analysing Human Movement ...

THE USE OF VIDEOGRAPHY IN RECORDING SPORTS MOVEMENTS
Background
QUANTITATIVE ANALYSIS OF MOVEMENT
Quantitative biomechanical analysts are mainly interested in improving performance
and reducing injury risk. They use a mixture of experimental and theoretical
approaches to seek answers to such questions as: What is the best running technique
to minimise energy expenditure? How should the sequence of body movements be
coordinated in a javelin throw to maximise the distance thrown? Why are lumbar spine
injuries so common among fast bowlers in cricket?
As we noted in Chapter 1, we can identify two fundamentally different approaches
to experimental movement analysis in sport – qualitative analysis and quantitative
analysis; the latter requires detailed measurement and evaluation of the measured data.
Earlier chapters in this book had a strong bias towards qualitative analysis whereas this
chapter, along with Chapters 5 and 6, will focus mostly on quantitative analysis.
The quantitative experimental approach often takes one of two forms, usually
referred to as the cross-sectional and longitudinal approaches. A cross-sectional study,
for example, might evaluate a sports movement by comparing the techniques of different
sports performers recorded at a particular competition. This can lead to a
better overall understanding of the biomechanics of the skill studied and can help
diagnose faults in technique. An alternative cross-sectional approach, which is less
frequently used, is to compare several trials of the same individual, for example a series
of high jumps by one athlete in a competition or in a training session. This is done to
identify the performance variables that correlate with success for that athlete. In a
longitudinal study, the same person, or group, is analysed over a longer time to improve
their performance; this probably involves providing feedback and modifying their
movement patterns. Both the cross-sectional and the longitudinal approaches are
relevant to the sports biomechanist, although conclusions drawn from a cross-sectional
study of several athletes cannot be generalised to a single athlete, or vice versa.
Movement analysts now use single-individual designs far more than in the past,
recognising that group designs often obscure differences between individuals in the
group and, indeed, the group mean may not apply to any single individual. After all,
most athletes are mainly interested in factors that affect their performance or might
be an injury risk for them. In a case study, a single person may be analysed on one or
just a few occasions; this approach is often used when assessing an injured athlete.
A single-individual design usually involves studying that person across time; multiple
single-individual designs study individual members of a group of performers across
time. This also gives the analyst a chance to use a group design simultaneously with the
multiple single-individual study. In such studies, it has been recommended that, for
reasonable statistical power, 20 trials per person should be analysed for a group of five
performers; for a group of 10 performers, 10 trials each; for a group of 20, five trials
each.
To give it a theoretical underpinning, an experimental study should be used in
conjunction with a theoretical approach, such as the use of deterministic models or
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