BIOMECHANICS AS AN INTERDISCIPLINE - Biomechanics and Motor Control of Human Movement - page 3

and diagnosing the causes. If measurements can be made during the patient's
movement, then data can be presented in a convenient manner to describe
the movement quantitatively. Here the assessor's task is considerably sim-
plified. He or she can now quantify changes, carry out simple analyses, and
try to reach a more objective diagnosis. At the highest level of assessment,
the observer can view biomechanical analyses that are extremely powerful in
diagnosing the exact cause of the problem, compare these analyses with the
normal population, and monitor their detailed changes with time.
The measurement and analysis techniques used in an athletic event could
be identical to the techniques used to evaluate an amputee's gait. However, the
assessment of the optimization of the energetics of the athlete is quite different
from the assessment of the stability of the amputee. Athletes are looking for
very detailed but minor changes that will improve their performance by a
few percentage points, sufficient to move them from fourth to first place.
Their training and exercise programs and reassessment normally continue
over an extended period of time. The amputee, on the other hand, is looking
for major improvements, probably related to safe walking, but not fine and
detailed differences. This person is quite happy to be able to walk at less
than maximum capability, although techniques are available to permit training
and have the prosthesis readjusted until the amputee reaches some perceived
maximum. In ergonomic studies, assessors are likely looking for maximum
stresses in specific tissues during a given task, to thereby ascertain whether
the tissue is working within safe limits. If not, they will analyze possible
changes in the workplace or task in order to reduce the stress or fatigue.
1.1.1 Measurement, Description, and Monitoring
It is difficult to separate the two functions of measurement and description.
However, for clarity the student should be aware that a given measurement
device can have its data presented in a number of different ways. Conversely,
a given description could have come from several different measurement
devices.
Earlier biomechanical studies had the sole purpose of describing a given
movement, and any assessments that were made resulted from visual inspec-
tion of the data. The description of the data can take many forms: pen recorder
curves, plots of body coordinates, stick diagrams, or simple outcome mea-
sures such as gait velocity, load lifted, or height of a jump. A movie camera,
by itself, is a measurement device, and the resulting plots form the description
of the event in time and space. Figure 1.2 illustrates a system incorporating
a cine camera and two different descriptive plots. The coordinates of key
anatomical landmarks can be extracted and plotted at regular intervals in
time. Time history plots of one or more coordinates are useful in describing
detailed changes in a particular landmark. They also can reveal to the trained
eye changes in velocity and acceleration. A total description in the plane of
the movement is provided by the stick diagram, in which each body segment