BIOMECHANICS AS AN INTERDISCIPLINE - Biomechanics and Motor Control of Human Movement - page 11

mechanisms involved and into movement strategies and compensations of
the neural system. A large part of the future of biomechanics lies in kinetic
analyses, because the information present permits us to make very definitive
assessments and interpretations.
As with the kinematics, all basic kinetic concepts will be covered in detail
in 2D analyses. Three-dimensional analysis adds an additional force vector in
the global reference system (GRS), but, because of the two additional planes,
there are two additional moment vectors. The 3D analysis techniques are
considerably more complex; however, within any of these three planes, the
interpretation is the same as in 2D analyses.
1.3.4 Anthropometry
Many of the earlier anatomical studies involving body and limb measure-
ments were not considered to be of interest of biomechanics. However, it is
impossible to evolve a biomechanical model without data regarding masses
of limb segments, location of mass centers, segment lengths, centers of rota-
tion, angles of pull of muscles, mass and cross-sectional area of muscles,
moments of inertia, and so on. The accuracy of any analysis depends as
much on the quality and completeness of the anthropometric measures as on
the kinematics and kinetics.
1.3.5 Muscle and Joint Biomechanics
One body of knowledge that is not included in any of the preceding categories
is the mechanical characteristics of the muscle itself. How does its tension
vary with length and with velocity? What are the passive characteristics of
the muscle — mass, elasticity, and viscosity? What are the various character-
istics of the joints? What are the advantages of double-joint muscles? What
are the differences in muscle activity during lengthening versus shortening?
How does the neural recruitment affect the muscle tension? What kind of
mathematical models best fit a muscle? How can we calculate the center
of rotation of a joint? The final assessment of the many movements cannot
ignore the influence of active and passive characteristics of the muscle, nor
can it disregard the passive role of the articulating surfaces in stabilizing
joints and limiting ranges of movement.
1.3.6 Electromyography
The neural control of movement cannot be separated from the movement
itself, and in the electromyogram (EMG) we have information regarding the
final control signal of each muscle. The EMG is the primary signal to describe
the input to the muscular system. It gives information regarding which muscle
or muscles are responsible for a muscle moment or whether antagonistic