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The summary of the
accompanying article and the PowerPoint slideshow
should be essential reading for any sports scientist working with athletes.
You don’t have to be in such a role very long before a coach will want to
know if an individual athlete is increasing or decreasing their score on a
particular test compared with their previous test or tests. They might well
ask, is an increase of a VO2max from 5.01 to 5.05 L/min “real”? To
answer them it means that you need to know how much an elite athlete is
likely to change over a finite period and how much noise is associated with
the measure. This work by Will Hopkins combines elements from several of his
previous publications, improves and simplifies them, and now provides a clear
pathway to answer a concerned coach or athlete.
The slideshow starts with a simplified
account of how the variation in performance of individual elite athletes in competition
gives rise to a "worthwhile" change: an enhancement that increases
medal-winning prospects of one of the athletes in a well-matched group. Novel
in this slideshow is Hopkins
attempt to quantify a worthwhile change for a team sport athlete. He has
chosen 0.2 of the between subject standard deviation (SD). This is a useful
start point but, as he indicates, there is no known relationship between
fitness test performance and team performance. For instance, teleologically,
it makes sense that fast sprint speed and high aerobic power would be
advantageous in a team sport such as soccer, but the ball handling and
game-reading skills also come into play with the team results. Furthermore,
at higher levels of competition a group may be more homogeneous and thus the
between subject standard deviation will also be reduced. Nevertheless, it
follows that worthwhile increments are also smaller as athletes rise toward
the top of any measure.
Hopkins reminds us of the importance of both test validity and reliability,
and that reliability is paramount. In Australia, we have been working for
more than 10 years, with the geographically remote state sport institutes, to
quantify test-retest reliability as a means to understand laboratory and
field physiology tests, such VO2max and 20-m sprint times (Gore,
2000). First we worked on test reliability and after a number of years we
moved toward test accuracy, whereby as much equipment as possible is
calibrated against first principles of time, distance and mass. Incorrectly,
we used total error of measurement to quantify our reliability, but have
subsequently used typical error (Hopkins,
2000) to quantify test-retest error and found little difference, owing to
small changes in the mean.
Hopkins suggests that you can use published studies to identify reliable
tests that you may wish to use for athlete testing. Our experience in Australia in
the field of exercise physiology suggests that it is essential that you
establish your own typical error using your own athletes and own equipment.
It is poor science to rely on others and assume that your error is as low as
theirs. You owe it to your athletes and coach to quantify the likely error of
a given test in your hands. This can be achieved readily by conducting a
test-retest a few days apart on your athletes in a specific squad. Hopkins notes that
longer periods between tests, when athletes begin to show individual changes
in fitness, are appropriate in the context of interventions of similar
duration.
Hopkins recommends using likely limits as a suitable method to provide
feedback to coaches and athletes. In Australia our state sports
institutes have adopted the "rules" approach as being most
expedient. We have also been conservative and sometimes interpreted that
useful changes are at least greater than ‘√2 x noise’, which means at
worst we are right more than 62% of the time. Contrary to Hopkins' advice we even use a 95% level of
confidence when using skinfolds (Woolford and Gore, 2004). This measure is
not really a performance test, but thoughtless interpretation can have
profound consequences with athlete body image and even eating habits. Thus,
in this rare case, I believe that such a conservative approach is
warranted.
Hopkins summarizes that you should be up front about the noise when you
feed back the test results to an athlete of coach. All reports of
physiological tests issued to athletes by our state sport institutes follow
that format with the test-specific Typical Error included and a note in the
footer explaining the rules for interpretation.
Overall, I believe that anyone working
with small groups of athletes is flying blind if they don’t know the typical
error of the tests they are using. Interpreting meaningful or worthwhile
changes in test results has been considered a bit of an art in some circles,
but the science of Hopkins' approach allows one to confident about the degree
of uncertainty of their recommendations.
Gore C (2000). Quality assurance in
exercise physiology laboratories. In: Gore CJ, editor. Physiological Tests
for Elite Athletes. Champaign,
IL: Human Kinetics, pp 3-11.
Hopkins WG (2000). Measures of reliability in sports medicine and
science. Sports Medicine 30, 1-15.
Woolford SM, Gore CJ (2004). Interpreting
skinfold sums. Use of absolute or relative typical error? American Journal of
Human Biology 16, 87-90.
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Published Nov 2004
©2004
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