Introduction to Sports Biomechanics: Analysing Human Movement ...

QUANTITATIVE ANALYSIS OF MOVEMENT
Figure 4.14 Tangential velocity and tangential and centripetal acceleration components for a gymnast rotating about a
bar. Her angular velocity vector lies along the bar as shown by the blue arrow; the position vector (dashed white arrow)
runs from the bar to the gymnast’s centre of mass. The tangential velocity vector (black arrow) is perpendicular to the position
vector and passes posterior to her centre of mass. The tangential acceleration vector is also represented by the black arrow.
The centripetal acceleration vector, shown by the continuous white arrow, is in the direction opposite to that of the position
vector.
human performer. Most of these conventions have certain problems, one of which is to
have an angle convention that is easily understood. Further discussion of this topic is
beyond the scope of this book (but see Milner, 2007; Further Reading, page 152).
The specification of the angular orientation of the human performer as a whole is
also problematic. The representation of Figure 4.15, for example, has been used to
analyse airborne movements in gymnastics, diving and trampolining. In this, rotation is
specified by the somersault angle (φ) about a horizontal axis through the centre of mass,
the twist angle (ψ) about the longitudinal axis of the performer, and the tilt angle (θ).
The last named is the angle between the longitudinal axis and the fixed plane normal to
the somersault angular velocity vector.
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