MOVEMENT STRATEGY AND ARM USE REDISTRIBUTE SIT-TO-STAND JOINT MOMENTS
1
Jason C. Gillette, 2Catherine A. Stevermer and 3Michelle Hall
1
2
Iowa State University, Ames, IA, USA
Des Moines University, Des Moines, IA, USA
3
University of Melbourne, Victoria, Australia
email: gillette@iastate.edu
INTRODUCTION
METHODS
The capability to move from a sitting to a standing
position is essential for mobility and is associated
with independent living. For those who struggle
with sit-so-stand, potential compensations include
utilizing different movement strategies [1-3] and
using armrest support. Three common sit-to-stand
movement strategies are momentum, stabilization,
and vertical. The momentum strategy involves
trunk/hip flexion to generate momentum and then
trunk/hip/knee extension to complete the sit-tostand movement. This is the most common strategy
utilized by young, healthy adults. The stabilization
strategy involves trunk/hip flexion to achieve a
stable ‘nose over toes’ posture, then knee extension,
and then trunk/hip extension. Such a strategy may
be preferred by someone with balance deficits
and/or fear of falling. The vertical strategy involves
knee/hip extension without trunk/hip flexion to rise
straight up from a sitting position during sit-tostand. Although difficult even for some young
healthy adults, this movement strategy may be
required for those with low back pain, during
pregnancy, or after total hip replacement. The use of
armrest support should be beneficial to those with
strength deficits such as hip extensor weakness and
may be particularly helpful for those who utilize the
vertical strategy.
Twenty-two individuals (gender 10 M/12 F, age
23±2 yr, height 1.71±0.08 m, mass 78±20 kg)
participated in this study. Verbal cues were
‘normal’ and ‘regular’ for the momentum strategy;
‘forward bending’ and ‘nose over toes’ for the
stabilization strategy; and ‘keep back straight’ and
‘do not bend forward’ for the vertical strategy. The
seated surface was a 46 cm wooden bench with no
back support. When using arm support, hands were
placed on 9 cm armrests attached to the bench.
After demonstration and practice, each participant
completed 3 repetitions of 6 conditions (3
movement strategies x 2 arm support options).
Twenty-four reflective markers were tracked during
the sit-to-stand movements by an 8-camera motion
analysis system (Vicon). Participants placed each
foot on a separate in-ground force platform (AMTI).
The purpose of this study was to determine lower
extremity joint moments during sit-to-stand as a
function of movement strategy and arm use. It was
hypothesized that the stabilization strategy would
result in increased hip extension moments and the
vertical strategy would result in increased knee
extension moments. It was also hypothesized that
the use of arm support would result in reduced hip
extension moments.
Sit-to-stand movements were analyzed from
elevation onset to vertical stabilization as
determined from the combined right and left vertical
ground reaction forces [4]. Using inverse dynamics,
right and left maximum ankle plantarflexion, knee
extension, external knee valgus, hip extension, and
hip abduction moments were calculated,
transformed to the distal segment coordinate
system, and normalized by body mass. All
calculations were determined using Matlab,
averaged across 3 trials, and averaged for right and
left legs. Multivariate ANOVA was used to test for
main effects of movement strategy, arm support,
and their interactions with a significance level of
p<0.05 (SPSS). When significant main effects were
found, post hoc Scheffe comparisons were utilized
for movement strategy effects and univariate
ANOVA for arm support effects with a Bonferroni
adjustment of 5 (p<0.01).
RESULTS AND DISCUSSION
Significant differences in peak joint moments as a
function of movement strategy and arm support are
shown in Table 1. Ankle plantarflexion moments
were decreased with the vertical strategy and
increased with the stabilization strategy. Knee
extension moments were decreased with the
stabilization strategy and increased with the vertical
strategy. Knee extension moments were also
decreased with armrest support. Hip extension
moments were decreased with the vertical strategy
and with armrest support. Hip extension moments
approached a significant increase when using the
stabilization strategy (p=0.013). Knee extension and
hip extension moments were dependent upon both
movement strategy and arm support, thus meriting
further examination. Knee extension moments
ranged from 0.435±0.127 Nm/kg when using the
stabilization strategy with armrest support to
0.804±0.122 Nm/kg when using the vertical
strategy with no arm support. Hip extension
moments ranged from 0.475±0.148 Nm/kg when
using the vertical strategy with armrest support to
0.909±0.161 Nm/kg when using the stabilization
strategy with no arm support. Knee valgus and hip
abduction moments were not significantly changed
by movement strategy or arm support.
The hypothesis that hip extension moments would
increase with the stabilization strategy was not
supported, although this comparison approached
significance. The hypothesis that knee extension
moments would increase with the vertical strategy
was supported by a 20% increase. The hypothesis
that hip extension moments would decrease with
armrest support was supported by a 24% reduction.
In terms of percent differences, the most dramatic
changes were a 36% increase in ankle plantarflexion
moments with the stabilization strategy and a 44%
reduction in ankle plantarflexion moments with the
vertical strategy. These distinct changes were likely
due to differences in peak ankle dorsiflexion angle
between the movement strategies.
Results of this study can be used to make basic
observations regarding sit-to-stand movements. The
stabilization strategy was described as an option for
those with balance deficits and also may also
benefit those with knee extensor weakness.
However, the stabilization strategy relies more
heavily on ankle plantarflexors and strengthening
exercises may be in order. The vertical strategy was
listed as an alternative for individuals with back/hip
pain or reduced range of motion and succeeded in
reducing hip extensor and even ankle plantarflexor
requirements. However, the vertical strategy has
higher knee extensor requirements, potentially
exceeding strength capacity, but which may be
offset by the use of armrests.
REFERENCES
1. Schenkman ML, et al. Clin Biomech 11, 153-158,
1996.
2. Mazza C, et al. J Am Geriatr Soc 52, 1750-1754,
2004.
3. Scarborough DM, et al. J Rehabil Res Dev 44, 3342, 2007.
4. Gillette JC, Stevermer CA. Gait Posture 35, 7882, 2012.
Table 1: The effects of movement strategy and arm support on sit-to-stand joint moments.
Peak Joint Moments (Nm/kg)
Ankle
Knee
Knee
Hip
Hip
Plantarflexion
Extension
Valgus
Extension
Abduction
Momentum
0.092 ± 0.063
0.732 ± 0.193
0.266 ± 0.102
0.281 ± 0.110
0.651 ± 0.127
Stabilization
0.834 ± 0.164
0.272 ± 0.125
0.381 ± 0.148↑
0.504 ± 0.145↓ 0.090 ± 0.061
Vertical
0.158 ± 0.091↓
0.781 ± 0.115↑ 0.112 ± 0.079
0.591 ± 0.201↓ 0.284 ± 0.151
No Support
0.104 ± 0.071
0.816 ± 0.196
0.287 ± 0.141
0.255 ± 0.149
0.691 ± 0.155
Armrests
0.292 ± 0.148
0.600 ± 0.177↓ 0.093 ± 0.065
0.622 ± 0.179↓ 0.261 ± 0.110
↑ indicates significant increases with respect to momentum strategy (p<0.01), ↓ indicates significant decreases
with respect to momentum strategy or no arm support (p<0.01)