Introduction to Sports Biomechanics: Analysing Human Movement ...

Figure 1.2 Reference postures (positions): (a) fundamental and (b) anatomical.
MOVEMENT PATTERNS – THE ESSENCE OF SPORTS BIOMECHANICS
By and large, this chapter focuses on movements in the sagittal plane about the
frontal (or mediolateral) axis of rotation (Figure 1.1(a)). Consider viewing a person
side-on, as in Figure 1.3; he bends his elbow and then straightens it. We call these
movements flexion and extension, respectively, and they take place in the sagittal plane
around the frontal axis of rotation. Flexion is generally a bending movement, with
the body segment – in the case of the elbow, the forearm – moving forwards. When the
knee flexes, the calf moves backwards. The movements at the ankle joint are called
plantar flexion when the foot moves downwards towards the rear of the calf, and
dorsiflexion when the foot moves upwards towards the front of the calf.
The movement of the whole arm about the shoulder joint from the anatomical
reference position is called flexion, and its return to that position is called extension;
the continuation of extension beyond the anatomical reference position is called
hyperextension. The same terminology is used to define movements in the sagittal plane
for the thigh about the hip joint. These arm and thigh movements are usually defined
with respect to the trunk.
Sports biomechanists normally use the convention that the fully extended position
of most joints is 180°; when most joints flex, this angle decreases. Clinical biomechanists
tend to use an alternative convention in which a fully extended joint is 0°,
so that flexion increases the joint angle. We will use the former convention throughout
5