BIOMECHANICS AS AN INTERDISCIPLINE - Biomechanics and Motor Control of Human Movement - page 6

Figure 1.4 Schematic diagram to show the relationship between the neural, kinetic,
and kinematic variables required to describe and analyze human movement.
filter (which mathematically has the same transfer function as that between a
neural pulse and its resultant muscle twitch). A more complex biomechanical
analysis could involve a link-segment model, and with appropriate kinematic,
anthropometric, and kinetic output data, we can carry out analyses that could
yield a multitude of significant time-course curves. Figure 1.4 depicts the
relationships between some of these variables. The output of the movement
is what we see. It can be described by a large number of kinematic vari-
ables: displacements, joint angles, velocities, and accelerations. If we have
an accurate model of the human body in terms of anthropometric variables,
we can develop a reliable link-segment model. With this model and accu-
rate kinematic data, we can predict the net forces and muscle moments that
caused the movement we just observed. Such an analysis technique is called
an inverse solution . It is extremely valuable, as it allows us to estimate vari-
ables such as joint reaction forces and moments of force. Such variables are
not measurable directly. In a similar manner, individual muscle forces might
be predicted through the development of a mathematical model of a muscle,
which could have neural drive, length, velocity, and cross-sectional area as
inputs.
1.1.3 Assessment and Interpretation
The entire purpose of any assessment is to make a positive decision about a
physical movement. An athletic coach might ask, “Is the mechanical energy
of the movement better or worse than before the new training program was
instigated, and why?” Or the orthopedic surgeon may wish to see the improve-
ment in the knee muscle moments of a patient a month after surgery. Or a
basic researcher may wish to interpret the motor changes resulting from cer-
tain perturbations and thereby verify or negate different theories of neural
control. In all cases, if the questions asked yield no answers, it can be said
that there was no information present in the analysis. The decision may be
positive in that it may confirm that the coaching, surgery, or therapy has
been correct and should continue exactly as before. Or, if this is an initial
assessment, the decision may be to proceed with a definite plan based on