Sit-to-Stand Movement Pattern A Kinematic Study - Physical Therapy

from the horizontal axis or 10 degrees to the right of the
vertical axis. The neck segment was 63 degrees from the
horizontal axis or inclined forward 27 degrees from the vertical
axis. The angle of the Frankfort plane from the horizontal
axis was negative, with the head tipped down 2 degrees. The
pelvic segment was 116 degrees from the horizontal axis or
rotated 26 degrees to the left of the vertical axis. The hip was
flexed to 135 degrees and the knee to 95 degrees. The relative
ankle measurement was 106 degrees (Table).
During the first 35% of the movement cycle, the angle of
the Frankfort plane from the horizontal axis indicated the
head was tipping downward. The angle of inclination changed
from an initial —2 degrees to a minimum of —6 degrees, at
which time 30% of the movement cycle had been completed.
Throughout the remainder of the movement cycle, the head
rotated upward from -6 to +4 degrees.
The neck, trunk, and pelvis followed similar patterns, moving
first into flexion and then into extension as the movement
cycle progressed. The neck angle inclined downward for the
first 35% of the movement cycle and then moved back toward
the vertical axis. The trunk began to move toward the vertical
axis after 45% of the movement cycle was completed. The
pelvis, initially in a position of posterior tilt with respect to
the vertical axis, rotated anteriorly from this position throughout
the first half of the movement cycle. This movement
reflected a change from 26 degrees behind the vertical axis to
12 degrees forward of the vertical axis. During the latter half
of the movement cycle, the pelvis reversed its direction,
ending in an upright position.
The hip flexed during the first 40% of the sit-to-stand
movement cycle and extended during the last 60% of the
cycle. The knee extended throughout the pattern of motion.
The ankle moved toward dorsiflexion in the first 45% of the
movement cycle. The remainder of the motion was characterized
by movement toward plantar flexion. Across all angles,
variability increased from distal to proximal and from caudal
to cephalic. The variability was smallest for each angle at the
termination of the movement cycle.
Movement Trajectories
Trajectories of various anatomical landmarks were constructed
to demonstrate the movement of these body parts in
space during the sit-to-stand task. Figure 3 (right diagram)
plots the movements of the data points on the mid-Frankfort
plane, acromion, midiliac crest, greater trochanter, and lateral
femoral epicondyle. The trajectories of the data points on the
mid-Frankfort plane and the acromion were similar, but the
excursion of the data point on the head was greater than that
of the acromion. The shapes of the trajectories of the midiliac
crest and greater trochanter also were similar. Their ascents
were more direct than those of the head or acromion, but still
curvilinear. The dip at the end of the movement of the
midiliac crest occurred as the pelvis moved from a posterior
position to an anterior position with respect to the vertical
axis. During this same time period, the greater trochanter
moved forward rather than downward.
Horizontal displacement at the knee was much greater than
vertical displacement. The knee trajectory demonstrated forward
and slightly downward displacement during earlier portions
of the movement pattern. This movement was followed
by backward and minimal upward movement as the knee
extended.
DISCUSSION
The sit-to-stand movement pattern can be divided into two
phases. The first phase, the flexion phase, occurred during the
first 35% of the movement cycle. The second phase, the
extension phase, then began at the head and knee. This change
was evidenced by a reversal of head movement and a rapid
increase in knee extension. The reversal of movement spread
from the head down the trunk to the pelvis. The reversal from
flexion to extension appeared to correspond to the lifting of
the buttocks from the chair. Because the chair was not
equipped with either a force transducer or a contact switch,
however, we were unable to document this relationship.
The body segment initiating the sit-to-stand movement
could not be identified in this study because of the distortion
inherent in the kinematic data. This problem, however,
prompted our analysis of the initial 20% of the movement
cycle to determine those angles demonstrating the greatest
displacement during that part of the cycle. The angle of the
Frankfort plane with respect to the horizontal axis (Angle 7)
demonstrated the highest frequency of maximal displacement
for 23 of the 55 subjects. When considering the hip and trunk
movements together, however, we noted that 25 subjects
exhibited maximal displacement at those angles (Angles 3
and 5) during the first 20% of the movement cycle. These
data suggest that substantial individual differences exist during
the initial phase of the movement cycle. For those individuals
who demonstrate the greatest angular displacement at the
Frankfort plane, this displacement may occur because the
head is leading the movement. Another possible explanation
is that the head displacement may be the result of movement
caudally to the head (ie, hip or trunk movement effecting
displacement at the head).
When group data are used to describe and to develop a
model of the sit-to-stand movement pattern, individual differences
are obscured. Our model, therefore, should not be
construed as directly applicable to all persons. Examination
of individual trajectories, nevertheless, allowed the grouping
of certain body parts. Although we did not analyze these
groupings further in this study, they suggest not only individual
variation but also common characteristics among individuals.
Future studies, thus, should be directed toward clarifying
these similarities and differences by considering the effects of
sex, age, and anthropometric variables on movement among
various body segments and the trajectories of body parts in
space.
Comparing data acquired in this study to those of earlier
reports is limited primarily by differences in methodology.
This study solely considered kinematic variables or time-space
relationships. No attempt was made to study the forces involved
in the sit-to-stand movement, as did Kelley et al. 5
Jones and associates 1-4 also examined the time-space characteristics
of the sit-to-stand movement, but important differences
exist between our approaches, goals, and presentation
of data. Although Jones and associates considered various
experimental conditions, they focused their attention on head
and neck movements. They reported descriptive data of other
body parts but did not document their findings with quantitative
data. The groups of subjects they used generally were
small and exclusively male, and they usually were instructed
to perform the task as quickly as possible.
1712 PHYSICAL THERAPY
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