Introduction to Sports Biomechanics: Analysing Human Movement ...

STUDY TASKS
QUANTITATIVE ANALYSIS OF MOVEMENT
1 Explain why quantitative video analysis is important in the study of sports
techniques.
Hint: You may find it useful to reread the section on ‘Comparison of qualitative
and quantitative movement analysis’ in Chapter 1 (pages 36–40) as well as the
section on ‘The use of videography in recording sports movements’ near the start of
this chapter (pages 117–20).
2 Obtain a video recording of a sports movement of your choice. Study the recording
carefully, frame by frame. Identify and describe important aspects of the technique,
such as key events that separate the various phases of the movement. Also, identify
the displacements, angles, velocities and accelerations that you would need to
include in a quantitative analysis of this technique. If you have access to a video
camera, you may wish to choose the sports movement you will use in Study
task 6.
Hint: You may find it useful to reread the section on ‘Identifying critical features of
a movement’ in Chapter 2 (pages 59–72) before undertaking this task.
3 (a) List the possible sources of error in recorded movement data, and identify
which would lead to random and which to systematic errors.
(b) Briefly describe the procedures that would minimise the recorded error in a
study of an essentially two-dimensional movement. Assess which of these steps
could not be implemented if video recording at an elite sports competition.
Briefly explain how these procedures would be modified for recording a threedimensional
movement.
Hint: You should reread the section on ‘Experimental procedures’ (pages 126–33)
before undertaking this task.
4 Download the Excel workbook containing the data from one of the five speeds for
the walk-to-run transition study on the book’s website. The knee angles contained
in that workbook were calculated from filtered linear coordinates that had been
auto-tracked using markers. We will assume therefore that the angles in the workbook
are sufficiently noise-free to be able to estimate accurately the knee angular
velocities and accelerations from the simple numerical differentiation equations
below.
(a) Calculate the knee angular velocities (ω i) as follows, using Excel:
ω ι = (θ i+1 − θ i−1)/(2∆t), where ω i is the angular velocity at time interval (Excel
row) number i and θ ι+1 and θ ι−1 are the knee angles at time intervals (rows) i+1
and i−1, respectively. The denominator in the equation (2∆t) is the time interval
between times (rows) i+1 and i−1 and is 0.04 s. Tabulate your knee angular
velocity data in a new column in your Excel worksheet. Note that we cannot
estimate the angular velocities at the first and last instants of the knee angle–
time series.
(b) Calculate the knee angular accelerations (α i) as follows, using Excel:
α i = (ω i+1 − ω i−1)/(2∆t), where α i is the angular acceleration at time interval
(Excel row) number i and ω ι+1 and ω ι−1 are the knee angular velocities at time
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