Introduction to Sports Biomechanics: Analysing Human Movement ...

INTRODUCTION TO SPORTS BIOMECHANICS
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must predominate because of the explosive short duration of many sports movements,
such as a high jump take-off, which requires power – the rapid performance
of work (see below). In absorbing momentum, as when catching a cricket ball,
the time is increased by ‘giving’ with the ball to reduce the mean impact force,
preventing bruising or fracture and increasing success.
Maximising the acceleration path.
This principle arises from the work–energy relationship, which shows that a large
change in mechanical energy requires a large average force or the maximising of
the distance over which we apply force. This is an important principle in events
requiring speed and force, for example a shot-putter making full use of the width of
the throwing circle.
Stability
A wide base of support is needed for stability; this applies not only to static activities
but also to dynamic ones in which sudden changes in the momentum vector occur.
APPENDIX 2.2 OTHER EXAMPLES OF PHASE ANALYSIS OF SPORTS
MOVEMENTS
As noted in this chapter, phase analysis involves the breaking down of movements into
phases. The phases have biomechanically distinct roles in the overall movement
and each phase has easily identified phase boundaries, often called ‘key events’. The
duration of the phases can be determined – to the accuracy of the time resolution of the
recording system – for comparison between and within performers (hence the other
name, temporal analysis). Any phase analysis should start with a statement of the reason
for performing the analysis, which should preferably be done in the preparation stage
but can be delayed until later if video is recorded. The movement analyst then needs to
specify phases, identity their boundaries and determine their distinctive biomechanical
features. The examples below, in addition to that of the long jump in this chapter,
should clarify various aspects of phase analysis.
Phase analysis of ballistic movements
Ballistic movements, which include throwing, kicking and hitting skills, subdivide
into three phases: preparation or backswing; action; recovery or follow-through. In the
tennis serve, for example, the key events are:
The start of the preparation phase – the initiation of ball toss.
The end of the preparation phase, which is also the start of the action phase – this is
somewhat arbitrary, but could be defined as the racket reaching its lowest point
behind the server’s back.
The end of the action phase and start of recovery – impact of the racket and ball.