Analysis of Human Movement 467Select Key Joints
Select the joints where visible movement occurs. With
more complex movements, add more focus on the
joints that are particularly key for correct generation
of the movement, versus joint movements that may
be more gestural or supplementary in nature.
Identify Key Joint Movements
Identify the joint movements that occur in each
of the key joints in each phase of the movement.
Remember that movement terms refer to the direc-
tion of movement and not a joint position or angle.
For example, when you begin to rise from a parallel
first-position plié, the hip would be described as
undergoing extension because that is the direction
of the movement, even though if you stopped the
movement before its completion, the hip would
be in a position of flexion (relative to anatomical
position).
Identify Type of Muscle Contraction
Identification of the type of muscle contraction
requires an appraisal of external forces relative to
internal forces and the resultant direction of move-
ment (chapter 2). In dance, concentric contractions
are generally used to move the body or its segments
in a direction against gravity and to accelerate limbs.
Conversely, eccentric contractions are generally used
to move the body or its segments in the same direc-
tion as gravity and to decelerate limbs. Additionally,
isometric contractions are used to maintain the posi-
tion of the body or its segments with no apparent
joint movement occurring.
Identify Prime Movers
Once the type of muscle contraction has been iden-
tified, the prime movers can be easily determined.
Remember that with a concentric contraction the
prime movers will be the muscle group whose action
is in the same direction as the observed joint move-
ment, while with an eccentric contraction, the active
muscles are those whose action is opposite to the
observed joint movement. If you are having trouble
delineating the prime movers, imagine what joint
movements would occur if all the muscles around the
joints under observation relaxed. The prime movers
would then be the muscle groups that would have
to function to create or control movement in the
desired direction at each joint. If the goal is to have
no movement occur at a given joint but relaxation
results in movement, the muscle group with an action
opposing this movement would be working isometri-
cally to maintain the desired joint position.
As done in previous movement analyses, when
delineating the prime movers, first list them in terms
of the functional group (e.g., hip flexors) and then
provide specific examples (e.g., iliopsoas, rectus
femoris) obtained from figures 8.1 and 8.2 and table
8.1. Including the functional muscle group is recom-
mended because it provides a simple way of trying to
accurately reflect the muscles that would have to work
without having to refer to studies that investigate the
relative contribution of specific muscles with factors
such as the speed of motion, changes in line of pull
relative to the relevant axis of rotation in different
ranges of motion, secondary actions of agonists, and
the amount of resistance to the given motion. Then,
when providing specific sample muscles, choosing
primary muscles versus secondary muscles for the
given joint movement (table 8.1) will generally help
provide muscles that are responsible for generating a
large percentage of the necessary force and that are
operative under many conditions. However, if more
accuracy is necessary, referring to EMG and other
research studies can be helpful.Identify Key Stabilizers (Optional)
Remember that when a muscle contracts as discussed
in chapter 2, the muscle unpreferentially tends to
bring both of its attachments toward one another
(law of approximation). In many movements, isomet-
ric co-contraction of many muscles is occurring to
stabilize segments of the body and prevent unwanted
movement due to this law of approximation or due to
movement of body segments away from the center of
mass of the body. For example, when movements such
as brushes (dégagés) are performed, co-contraction of
many muscles of the hip and spine works to prevent
undesired compensations of the pelvis or torso.
To simplify movement analysis, emphasis is usu-
ally placed on the body segments that are moving.
However, it is important to realize that appropriate
functioning of these muscles of stabilization is key
for technique and injury prevention. In recognition
of their role, one approach is to include one or two
stabilizers that are essential to prevent common tech-
nique/alignment errors and allow proper execution
of the movement. Another approach is to address
stabilizers with technique considerations only if a
technique error is occurring that relates to inappro-
priate use of a stabilizer. For example, if one were
analyzing a movement, the function of the abdomi-
nal muscles as stabilizers to prevent hyperlordosis
(figure 8.3, p. 471) could be listed in a section titled
“stabilizers” or in a section addressing “alignment
and technique considerations” if excessive arching
of the low back was noted.