Analysis of Human Movement 485to make the arms rapidly fall back down to the sides,
and so the shoulder abductors work eccentrically to
control the lowering of the arms. A more detailed
analysis of this movement would take into account
the more specific effects of gravity. For example,
as the right arm passes a vertical position, such as
seen in table 8.5C, gravity would actually tend to
produce shoulder abduction rather than adduction,
and the right shoulder adductors would actually be
used eccentrically in the brief portion of the range
of motion to bring the arms to the full overhead
position, isometrically if position C was maintained,
and concentrically for the brief portion of the return
phase until the arm passes a vertical position.
Looking at the movement more specifically,
because of the challenge of balancing on one leg
as the trunk moves laterally and the large weight of
the gesture leg, many muscles work as stabilizers in a
highly coordinated manner to achieve desired posi-
tioning of the segments of the body. One important
example of stabilization occurs with the spine. In the
starting position, co-contraction of the spinal flexors
and extensors can be used to achieve the desired
approximately neutral alignment of the trunk with
the desired lift or presentation of the torso. However,
as the trunk moves laterally, gravity now plays a key
role, tending to produce lateral flexion of the trunk.
Now, as previously stated, the right lateral flexors
have to work approximately isometrically to keep
the desired neutral extended position of the spine.
Cueing students to “reach the spine out long and in
line with the middle of the sacrum” (vs. letting it fall
sideways—laterally tilt) as the trunk tilts primarily
from the hip joint can sometimes help achieve the
desired positioning.
In terms of synergists, the oblique abdominal
muscles have been shown to be key lateral flexors of
the spine. However, contraction of the right internal
oblique would also tend to produce undesired right
rotation and flexion of the spine. The right external
oblique could be used as a synergist to neutralize
undesired rotation, and the spinal extensors could
be used as synergists to neutralize undesired flexion
of the spine.
Considering strength and flexibility and focus-
ing on the end of the up-and-over phase of the
movement, it can be ascertained that inadequate
hip adductor flexibility, as well as inadequate hip
abductor strength, could limit the dancer’s ability to
achieve the desired height of the leg. If performed
turned out, inadequate hamstring flexibility and
inadequate hip flexor and hip external rotator
strength could also limit the height of the gesture
leg. Lastly, adequate strength and flexibility as well
as skilled activation of many muscles of the support
leg are vital for successful execution of this move-
ment.
In terms of technique, one common error is fail-
ure to keep the trunk movement primarily in the
frontal plane. The trunk is commonly flexed at the
hip joint, with the bottom of the pelvis going back
while the ribs project forward (excessive thoraco-
lumbar extension). In such a case, cueing to “keep
the sitz bones down and forward over the support
leg” (neutral position of hip extension via use of the
abdominal–hamstring force couple) while “the front
of the lower ribs are pulled down and slightly back”
(neutral position of the spine) can help achieve the
desired positioning.
In terms of special considerations, this movement
can be performed with many variations, including
off-center positions of the trunk and allowing marked
lateral tilt of the pelvis to maximize leg height. In the
latter case, marked right lateral flexion of the spine
is required in the tilt position to bring the shoulders
and eyes to an approximately horizontal position.
This demands marked spinal flexibility and strength
of the lateral flexors of the spine.Potential Benefits
of Anatomical Movement AnalysisAnatomical movement analysis can be used to help
improve performance of a given movement in
various ways. First, such an analysis results in the
determination of which muscles are acting as prime
movers. An understanding of the muscles acting as
prime movers can help with appropriate generation
of movement cues and strengthening exercises.
For example, in the front kick from a lunge, many
dancers aim to improve the height to which they
can lift the leg. Anatomical analysis and reference
to EMG studies reveal that the hip flexors, and espe-
cially the iliopsoas, are key for performance of this
movement in high ranges of motion. Hence, cues
aimed at emphasizing use of the iliopsoas, as well as
supplemental exercises that focus on strengthening
and activation of this muscle in a range of motion
similar to that required by the movement, should
result in improvement in leg height.
Anatomical analysis also yields potential flex-
ibility constraints for a given movement; and when
inadequate flexibility is operative, improving the
flexibility of these muscles can improve perfor-
mance of the given movement. So, in the front kick,
anatomical analysis reveals that adequate flexibility
of the hamstrings is key for maximizing the height
to which the leg can be lifted to the front, and