Introduction to Sports Biomechanics: Analysing Human Movement ...

The end of the recovery phase, which is also rather arbitrary and could be defined
as the end of the serving arm’s follow-through or the start of the player’s movement
into the next stroke.
Here, the preparation phase has various important functions:
It puts the body into an advantageous position for the action phase.
It maximises the range of movement of the racket – it increases the acceleration path
(see Appendix 2.1).
It allows the larger segments to initiate the movement (see Appendix 2.1).
It stretches the agonist muscles, increasing the output of the muscle spindle receptors,
and allowing the storage of elastic energy (the stretch–shortening cycle, see
Appendix 2.1).
It increases the length of the muscles responsible for the action (called the prime
movers or agonists, see Chapter 6) to that at which maximum tension is developed.
It provides neural facilitation (through the Golgi tendon organs) by contraction
of the group of muscles that may slow the movement in the recovery phase (the
antagonists).
The important functions of the action phase are:
Movements are initiated by the large muscle groups and continued by faster, smaller,
more distal muscles of the limbs, increasing the speed throughout the movement as
the segmental ranges of movement increase (see Appendix 2.1).
The accuracy of the movement increases through the recruitment of muscles with
progressively decreasing innervation ratio (see Appendix 2.1).
The segmental forces are applied in the direction of movement and movements are
initiated with minimum inertia as movement proceeds along the segment chain (see
Appendix 2.1).
The recovery phase:
QUALITATIVE ANALYSIS OF SPORTS MOVEMENTS
Involves controlled deceleration of the movement by, usually, eccentric (lengthening)
contraction of the appropriate antagonist muscles.
May achieve a position of temporary balance, as at the end of a golf swing.
For a learner, may require a conscious effort to overcome neural inhibition from the
Golgi tendon organs, which is reinforced by antagonistic muscle spindle activity.
Although phase analysis is very helpful in identifying critical features of a movement
and in building a deterministic model, it does have important limitations. The phase
boundaries need to be easily observable, but there is some arbitrariness in specifying
them, as in the tennis serve example above. The end of the backswing of the racket
might conveniently define transition from the preparation to the action phase; however
at that instant, the legs and trunk will be in their ‘action’ phase while the distal joints of
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