Introduction to Sports Biomechanics: Analysing Human Movement ...

Table 2.1 Examples of slowest satisfactory shutter speeds for various activities
ACTIVITY SHUTTER SPEED (s)
Walking 1/50
Bowling (lawn or tenpin) 1/50
Basketball 1/100
Vertical jump 1/100
Jogging 1/100 to 1/200
Sprinting 1/200 to 1/500
Baseball pitching 1/500 to 1/1000
Baseball hitting 1/500 to 1/1000
Soccer kicking 1/500 to 1/1000
Tennis 1/500 to 1/1000
Golf 1/1000 or faster
QUALITATIVE ANALYSIS OF SPORTS MOVEMENTS
Table 2.1. However, most movement analysts do not have routine access to high-speed
video cameras with sampling rates up to thousands of pictures per second. If your needs
analysis shows a clear requirement for such cameras, then this should be factored into
the project costing in the preparation stage.
When deciding where to conduct the study, we have to balance an environment in
which we have control over extraneous factors, such as lighting and background, and
one that is similar to that in which the movement is normally performed; the latter
ensures ecological validity. Normally, the latter dominates, but the decision may be
affected by the skill of the performers, whether the activities being recorded are open
or closed skills, and videographic issues. When selecting camera vantage points, the
movement analyst has to address from where he or she would want to view these
activities for qualitative analysis, with how many cameras, and whether the cameras
need to be stationary.
The decision of how many trials, or performances, to record is very important for
the reliability of qualitative analysis. However, that decision is not always made by the
movement analyst. For example, if you were recording from a game, say of football, for
notational analysis, you only have control over how many games you will record. If
recording for technique analysis in competition, the number of recordable trials is
probably fixed, for example, at six throws in the finals of a discus competition, the
heats plus the finals of swimming events, and as many attempts as the jumper needs
in the high jump until three failures. If recording out of competition, we need to
decide how many observations we need; generally, within reason, the more the better.
Because of movement variability, there is no such thing as a representative trial even
for stereotyped closed skills. The more trials we record, the more likely are our results
to be valid. Various rules of thumb have proposed between five and twenty trials
as a minimum requirement; ten, if you can record that many, is often highly
satisfactory.
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