Introduction to Sports Biomechanics: Analysing Human Movement ...

FUNDAMENTALS OF MOVEMENT
Motion in sport can be linear, rotational or, more generally, a combination of both.
Each type of motion is associated with a physical model of the sports performer or
sports object being studied. The behaviour of this physical model can be represented by
mathematical equations, which constitute a ‘mathematical model’ of the object or
performer. These mathematical models can then be used to investigate how the object
or performer moves.
Linear motion and the centre of mass – the ‘point’ model
Figure 3.3 Curvilinear motion.
MORE ON MOVEMENT PATTERNS – THE GEOMETRY OF MOTION
Linear motion is movement in which all parts of the body travel the same distance in
the same time in the same direction. If two points on the body are joined by a straight
line then, in successive positions, this straight line will remain parallel to its initial
orientation. Linear motion is often subdivided into rectilinear motion, which is onedimensional
(as for a puck travelling across an ice rink), or curvilinear, which can be
two- or three-dimensional (as for the centre of mass of a shot when in the air or the
centre of mass of a ski jumper). It is important to note that, although in curvilinear
motion the centre of mass – like the skis in Figure 3.3 – follows a curved path, no
rotation about the centre of mass is involved.
The overall linear motion of a sports performer or object, such as a shot, can be
specified by the motion of a single point. This imaginary point, which has the same
mass as the performer or object, is known as the centre of mass. The mass of the
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