Introduction to Sports Biomechanics: Analysing Human Movement ...

Requires less digitising time and has fewer methodological problems, such as the transformation
of coordinates from the video image to the ‘real world’ movement plane.
Three-dimensional recording and analysis:
Problems and sources of error in motion recording
QUANTITATIVE ANALYSIS OF MOVEMENT
Has more complex experimental procedures.
Can show the body’s true three-dimensional movements.
Requires more equipment and is, therefore, more expensive. Although it is possible by
intelligent placement of mirrors to record several images on one camera, this is rarely practical
in sports movements.
Has increased computational complexity associated with the reconstruction of the threedimensional
movement–space coordinates from the video images, and requires software
time synchronisation of the data from cameras that are not physically time-synchronised, as
for most digital video cameras.
Allows angles between body segments to be calculated accurately, without viewing distortions.
It also allows the calculation of other angles that cannot, in many cases, be easily
obtained from a single camera view. One example is the horizontal plane angle between the
line joining the hip joints and the line joining the shoulder joints, which can be visualised from
above even if the two cameras were horizontal.
Raises the problem of which convention to use for segment orientation angles, which twodimensional
analysis sidesteps.
Enables the reconstruction of simulated views of the performance (e.g. Figures 3.1(a) to (c))
other than those seen by the cameras, an extremely useful aid to movement analysis and
evaluation.
The recording of human movement in sport can be formally stated as: to obtain a
record that will enable the accurate measurement of the position of the centre of
rotation of each of the moving body segments and of the time lapse between successive
pictures. The following problems and sources of error can be identified in twodimensional
videography of sports movements:
The three-dimensionality of the position of joint centres of rotation requires the
two-dimensional analysis of movements recorded from one camera to be done with
care.
Any non-coincidence of the movement plane (the plane of performance) and the
plane perpendicular to the optical axis of the camera (the photographic plane) is
a source of error if calibration is performed with a simple scaling object in the plane
of motion.
Perspective and parallax errors need attention. Perspective error is the apparent
discrepancy in length between two objects of equal length, such as left and right
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