Introduction to Sports Biomechanics: Analysing Human Movement ...

MORE ON MOVEMENT PATTERNS – THE GEOMETRY OF MOTION
Identify the curvature of the various regions of the pattern – are they positive
(valley-type) or negative (hill-type); refer to Figure 3.7 if you have forgotten.
Check your answers with Figures 3.9(b) and (c). The gradient changes at the vertical
black lines in Figure 3.9(b) from positive to negative or from negative to positive; the
gradient is instantaneously zero at the vertical lines. The curvature changes, again from
positive to negative or vice versa, at the vertical blue lines in Figure 3.9(c); the curvature
is instantaneously zero at these vertical lines. The regions of flexion and extension
(Figure 3.9(b)), and those of positive and negative curvature (Figure 3.9(c)), are also
shown. Study these patterns very carefully and ensure that you understand them fully
before carrying on. If you were wrong, go back to Figure 3.9(a) and try to ascertain
where and why you went wrong.
Figure 3.10 is a combination of Figures 3.9(b) and (c), to which have been added the
angular velocity (continuous blue curve) and acceleration (dashed blue curve) patterns.
Angular velocity – the chain-dotted pattern – is positive when the knee is extending and
negative when it is flexing. The horizontal line marked 0 shows where the angular
velocity or acceleration is zero; values below this line are negative, those above are
positive. The angular acceleration – the continuous pattern – is positive, corresponding
to positive (valley-type) curvature of the knee angle curve, when it is driving the knee
from a flexed to an extended position; we can call this an extending acceleration. The
angular acceleration is negative, corresponding to negative (hill-type) curvature of the
Figure 3.10 Variation of knee angle (black curve), angular velocity (continuous blue curve) and angular acceleration (dashed
blue curve) with time in treadmill running. Vertical black lines separate positive (extension) and negative (flexion) slope
(velocity) and vertical blue lines separate positive and negative curvature (acceleration). The angle, angular velocity and
angular acceleration data have been ‘normalised’ to fit within the range −1 to +1.
95