BIOMECHANICS AS AN INTERDISCIPLINE - Biomechanics and Motor Control of Human Movement - page 12

activity is taking place. Because of the relationship between a muscle's EMG
and its tension, a number of biomechanical models have evolved. The EMG
also has information regarding the recruitment of different types of muscle
fibers and the fatigue state of the muscle.

1.3.7 Synthesis of Human Movement
Most biomechanical modeling involves the use of inverse solutions to predict
variables such as reaction forces, moments of force, mechanical energy, and
power, none of which is directly measurable in humans. The reverse of this
analysis is called synthesis , which assumes a similar biomechanical model,
and using assumed moments of force (or muscle forces) as forcing functions,
the kinematics are predicted. The ultimate goal, once a valid model has been
developed, is to ask the question, “What would happen if?” Only through
such modeling are we able to make predictions that are impossible to create
in vivo in a human experiment. The influence of abnormal motor patterns can
be predicted, and the door is now open to determine optimal motor patterns.
Although synthesis has a great potential payoff, the usefulness of such models
to date has been very poor and has been limited to very simple movements.
The major problem is that the models that have been proposed are not very
valid; they lack the correct anthropometrics and degrees of freedom to make
their predictions very useful. However, because of its potential payoff, it
is important that students have an introduction to the process, in the hope
that useful models will evolve as a result of what we learn from our minor
successes and major mistakes.

1.3.8 Biomechanical Motor Synergies
With the increased technology, biomechanics has made great strides in ana-
lyzing more complex total body movements and, because of the considerable
interactions between adjacent muscle groups, it is becoming necessary to
identify motor synergies. In a new chapter, we use several techniques to
identify two or more muscle groups acting synergistically toward a common
goal.

1.4 REFERENCES

Bernstein, N. A. The Coordination and Regulation of Movements . (Pergaman Press.
Oxford, UK, 1967).
DeLuca, C. J., R. A. LeFever, M. P. McCue, and A. P. Xenakis. “Control Scheme
Governing Concurrently Active Motor Units During Voluntary Contractions,''
J. Physiol. 329 :129 -142, 1982.
Henneman, E. and C. B. Olson. “Relations between Structure and Function in the
Design of Skeletal Muscle,'' J. Neurophysiol. 28 :581 - 598, 1965.