Introduction to Sports Biomechanics: Analysing Human Movement ...

SUMMARY
This chapter covered the principles of kinematics – geometry of movement – which are
important for the study of movement in sport and exercise. Our focus was very strongly
on movement patterns and their qualitative interpretation. Several other forms of
movement pattern were introduced, explained and explored – including stick figures,
time-series graphs, angle–angle diagrams and phase planes. We considered the types of
motion and the model appropriate to each. The importance of being able to interpret
graphical patterns of linear or angular displacement and to infer from these the
geometry of the velocity and acceleration patterns was stressed. We looked at two ways
of assessing joint coordination using angle–angle diagrams and, through phase planes,
relative phase; we briefly touched on the strengths and weaknesses of these two
approaches. Finally, a cautionary tale of unreliable data unfolded as a warning to the
analysis of data containing unacceptable measurement errors.
STUDY TASKS
MORE ON MOVEMENT PATTERNS – THE GEOMETRY OF MOTION
Although most studies in sports biomechanics have been digitised by only one operator, this
practice ignores the importance of assessing objectivity – although, from the results of the study
discussed here, this is usually justifiable if markers are used, the same is clearly not the case for
no-marker conditions. The results of this study also cast a shadow on previous results from
studies in sports biomechanics in which markers have not been used; this applies in particular to
those – and there are far too many – in which no attempt has been made to assess reliability or
objectivity. Unreliable data is clearly the bane of the quantitative analyst wishing to focus on
competition performance; it also presents problems for qualitative analysts whose movement
patterns in such conditions will be contaminated by errors.
1 Draw sketch diagrams from your own sport and exercise activities to show the three
types of motion – linear, angular and general – and the model appropriate to each.
List the uses and limitations of each model.
Hint: You may wish to reread the section on ‘Fundamentals of movement’
(pages 87–9) before undertaking this task.
2 (a) Download a knee angle–time graph for walking from the book’s website. From
this, and using the relationships between the gradients and curvatures of the
graph, sketch the appropriate angular velocity and acceleration graphs.
Remember that you move along the graph from left to right, going uphill and
downhill noting the changes in gradient and curvature.
(b) Repeat the above exercise for the hip angle in walking, which you can download
from the book’s website.
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