Introduction to Sports Biomechanics: Analysing Human Movement ...

these relates to within-performer movement and performance variability; as we noted
in the observation stage above, this can only be accounted for by recording multiple
trials. Identifying the source of movement errors can also be problematic as they
can arise from: body position or movement timing (biomechanical); conditioning
(physiological); the performer evaluating environmental cues (perceptual-motor); or
motivational factors (psychological). These factors support the need for movement
analysts to be able to draw on a range of disciplinary skills and knowledge. In the real
world of sport, movement analysts are usually most effective when they work as part of
a multidisciplinary team of experts. Analysis bias, reliability and objectivity also present
problems. Bias can be reduced by the use of ‘correctness’ criteria. Assessing reliability
and objectivity requires multiple trials or analysts respectively; the latter is often a
luxury, the former is vital.
Diagnosis of movement errors
QUALITATIVE ANALYSIS OF SPORTS MOVEMENTS
Perhaps the major issues in the evaluation and diagnosis stage relate to the lack of a
consistent rationale for diagnosing movement errors: our ‘critical features’ approach is
best, providing that we can identify and prioritise the correct critical features. As only
one intervention at any time is best, in the intervention stage, we need to focus on
one correction at a time. This raises the question of how we diagnose to prioritise
intervention. Five approaches are used, depending on the activity and circumstances.
The first of these focuses on ‘what came before’, in other words the relationship to
previous actions, as in a stroke sequence in tennis. The second, somewhat related to the
first, looks at the correct sequence through the phases of the movement (see Appendix
2.2). These two approaches are conceptually attractive, as problems usually arise before
they are spotted. For example, in our long jump model below, landing problems are
often due to poor generation of rotation on the take-off board or control of it in the air.
Some problems arise in implementing these approaches for complex multi-segmental
sports movements. We need to be aware that body segments interact, such that muscles
affect even joints they do not cross. For example, it is normal to record a lack of triceps
brachii activity in the action phase of baseball pitching, even though this muscle group
is the main extensor of the elbow. In throwing and kicking, it is not entirely clear if a
proximal segment speeds up a distal one or a distal one slows down a proximal one.
The third, and perhaps the most obvious, approach seeks to prioritise the critical
features that maximise performance improvement. To use the long jump model again,
if a long jumper is not jumping far, speed is overwhelmingly the most important factor;
so what critical feature would we prioritise to maximise performance? Run-up speed
obviously. However in many cases, it is not at all easy to know what will maximise
improvement; furthermore, we often need to balance short-term and long-term
considerations. In terms of successful outcomes, a fourth, and very attractive, approach
is to make the easiest corrections first, in order of difficulty. This is impeccably logical
from a motor skills viewpoint if movement errors seem unrelated and cannot be ranked.
However there is little, if any, clear support for its efficacy in improving performance.
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