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MEASURING GATE STABILITY WITH A WEARABLE ACCELEROMENTER IN FEMALE CLUB LACROSSE
ATHLETES
Segelke, H. R.1, Pitt, W. 1 and Chou, L1 1Motion Analysis Lab, Dept. of Human Physiology, University of Oregon, Eugene, OR USA
email: [email protected], web: http://biomechanics.uoregon.edu/MAL/
INTRODUCTION
Concussion incidence in female lacrosse players is nearly
equal to football players. As participation in lacrosse rapidly
grows, it presents a significant risk for increased head injury
incidence in female athletes. Commonly used concussion
assessments such as the ImPACT take 25 minutes to complete
while the SCAT5 cannot be performed in under 10 minutes.
Furthermore, current post-concussion return to play criteria
are based on athletes’ subjective symptom report, static
balance, and neurological assessment; metrics which return to
normal within 1-2 weeks. However, previous research has
demonstrated persistent gait stability deficits in acutely
concussed athletes for as long as 2 months post injury. As
such, the risk of early return to play is great which may lead
to an increase in risk for repeat concussion and
musculoskeletal injuries.
The purpose of this study was to employ a novel
accelerometer based, dual-task gait stability assessment in a
group of female lacrosse players to determine metrics
sensitive to changes in gait stability, and establish clinical
feasibility.
METHODS
Female athletes from the university club lacrosse team
underwent a single testing session in the motion analysis
laboratory. Three OPAL wearable motion sensors (APDM,
Inc., Portland, OR) were placed on the subject; one on the
lateral side of each ankle, and one over the L5 vertebrae as a
proxy for the whole body center of mass (COM). Subjects
performed three seated trials each of the auditory Stroop and
Q&A tasks. After static trials, each subject performed two
practice trials of a simple walking task in which they walked
at a self-selected pace over an eight-meter path, turned
clockwise around a cone, and returned to the start position.
Following practice trials, three trials each were performed in
each of three randomly presented conditions: single-task (ST)
walking, walking while performing an auditory Stroop test
(DT Stroop), and walking while performing a question and
answer (DT Q&A) test. Raw accelerometer and gyroscope
data were analyzed with a custom Matlab program (Fig.1).
The difference in various kinematic metrics between the ST
walking condition and the two DT conditions was the
performance cost associated with the application of the
secondary task (dual-task cost [DTC]).
RESULTS AND DISCUSSION
Seven female subjects (19.0±1.2 yrs, 167.1±3.5 cm, 64.9±12)
kg) completed the study. Average assessment time including
sensor placement was 9:21 min ± 57 sec. Analysis of linear
accelerations and angular velocities revealed a measurable
DTC in various temporal distance and COM kinematic
metrics. Average step time (p = .004), step velocity (p = .005)
and medial-lateral angular velocity (p = .048) all
demonstrated a significant DTC. There was a trend for greater
instability during DT Stroop and DT Q&A conditions for
other metrics, however, they did not reach a significant level.
DTC for the Q&A condition were generally larger than the
Stroop condition.
Figure 1: Acceleration profiles for a complete assessment.
Each trial is parsed into straight gait and turning gait.
CONCLUSIONS
The application of a wearable sensor based dual-task gait
assessment in female club lacrosse players revealed the
sensitivity of multiple acceleration/angular velocity gait
metrics to subtle differences in dynamic balance control.
Furthermore, an average time under 10 minutes demonstrates
the clinical feasibility of the assessment. These results support
the use of this instrument and protocol in the assessment of
gait balance control impairment following concussive injury.
ACKNOWLEDGEMENTS
This study was supported by the University of Oregon
Undergraduate Research Opportunity Program.
Table 1: Gait temporal distance metrics, peak Anterior-Posterior (AP) acceleration and deceleration, peak Medial-Lateral
(ML) accelerations between 35-50% and 50-65% of a gait cycle, and peak ML angular velocity. All data presented as mean
(SD). * indicates significant differences between conditions, p < .05
CAN ANGULAR MOEMNTUM PROTECT YOUR BRAIN DURING A FALL? ANALYSIS OF THE
ASSOCIATION BETWEEN LEG RAISE AND HEAD IMPACT DURING BACKWARD FALLS IN OLDER
ADULTS
Shishov N., Robinovitch S.N.
Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC CANADA
email: [email protected] , web: http://www.sfu.ca/tips.html
INTRODUCTION
Falls cause up to 80% of traumatic brain injuries (TBI) in
older adults [1]. Head impact occurs in over one-third of falls
in long-term-care (LTC) residents [2]. Backward falls create
the greatest risk for TBI [3]. Backward falls typically involve
impact to the pelvis before the torso or head. In the current
study, we analyzed video footage of real-life falls experienced
by older adults in LTC, to test the hypothesis, based on
angular momentum considerations (Figure 1), that torso
stabilization, and the probability for head impact, is reduced
by raising the legs after pelvis impact.
Figure 1. Angular momentum considerations in a backward
fall.
METHODS
From a database of 2321 videos of real-life falls in older
adults in LTC [4], we identified 215 strictly backward falls
where the pelvis and torso impacted the ground (Figure 2).
Head impact occurred in 85 falls. We analyzed the fall videos
to determine whether, at the instant of pelvis impact, the torso
was closer to the vertical or horizontal, and whether there was
observable raising of the legs after pelvis impact.
Figure 2. Examples of falls where (a) head impact occurred
and (b) head impact was avoided. The fall without head
impact involved leg raise and a trunk angle (at pelvis impact)
closer to the vertical. The fall with head impact involved no
leg raise and a trunk angle closer to the horizontal.
We used Chi-square to examine the associations between the
occurrence of head impact, the occurrence of leg raise, and
trunk angle at pelvis impact.
RESULTS AND DISCUSSION
Leg raise occurred in 69% of falls (n=148; Table 1). In falls
that involved leg raise, 28% involved head impact (n=41). In
falls that did not involve leg raise, head impact occurred in
66% of cases (n=44). There was a significant difference in the
frequency of head impact between falls with and without leg
raise (X2=27.8, p<0.0001). The odds for head impact were 4.9
times higher in falls that did not involve leg raise compared
to falls with leg raise [OR=4.9 (2.7-9.3)] (Figure 3).
Figure 3. Mosaic plot showing distribution of head impact
and leg raise.
The trunk angle at pelvis impact was closer to the vertical than
horizontal in 54% of falls (n=96; Table 1). Falls involving a
trunk angle closer to vertical were more likely to involve leg
raise than falls where the trunk angle was closer to horizontal
(81.3% versus 61.4%; X2=8.673, p=0.003).
We found that, during backward falls in older adults, leg raise
after pelvis impact was common, and reduced the odds for
head impact by nearly 5-fold. The presumed mechanism is
angular momentum that slows downward rotation of the torso
and head. Leg raise was facilitated by impacting the pelvis
with the torso vertical. Improved understanding is required on
how leg raise depends on passive dynamics versus active
neuromuscular responses, and on muscle strength and
flexibility. Exercise training, and a simple instruction to “raise
your legs after your pelvis contacts the ground,” may enhance
the natural tendency for humans to utilize this response for
protecting the head and brain during falls.
REFERENCES
[1] Fu WW, et al., PLoS ONE 12(4): e0175868, 2017.
[2] Schonnop R et al., Can Med Assoc J 185, E803-810, 2013.
[3] Hwang HF et al., J Head Trauma Rehabil 30, E9-17, 2015.
[4] Yang Y et al., JAMDA 19: 130-135, 2018.
ACKNOWLEDGEMENTS
This study was supported in part by CIHR (TEI-138295) and
AGE-WELL (WP5.2).
Table 1: Frequency of head impact and trunk angle, with and without leg raise. Head impact Trunk angle
Leg raise
Yes No Total Closer to horizontal Closer to vertical Total
No 44 (65.7%) 23 (34.3%) 67 (31.2%) 32 (38.6%) 18 (18.8%) 50 (27.9%)
Yes 41 (27.7%) 107 (72.3%) 148 (68.8%) 51 (61.4%) 78 (81.3%) 129 (72.1%)
Total 85 (39.5%) 130 (60.5%) 215 (100%) 83 (46.4%) 96 (53.6%) 179 (100%)
(a) (b)
FATIGUE AFFECTS BALANCE CONTROL DIFFERENTLY DURING SINGLE- AND DUAL-TASK WALKING IN OLDER WORKERS Chen, S-H and Chou, L-S
Department of Human Physiology, University of Oregon, Eugene, OR, USA email: [email protected], web: http://choulab.uoregon.edu
INTRODUCTION Older adults are more likely to perform daily physical activities or work at levels close to their maximal capabilities [1] and experience fatigue. Given the increasing participation rate in labor force of older adults and the positive association between fatigue and fall injuries [2], it is important to investigate the effects of fatigue during walking, especially perturbed walking when falls most often occur. Impact of fatigue on gait performance could be amplified when cognitive demand increases [3]. Walking and simultaneously performing an attention demanding task could occur with fatigue at the end of a job performance. Therefore, the purpose of this study is to investigate the effect of fatigue on gait balance control during dual-task level walking and obstacle-crossing in older workers. METHODS Seven older workers (4 females, 61.4 ± 5.1 yrs) performed the following five tasks before and after a fatigue protocol with in a random order: 1) walking at a self-selected comfortable speed (WALK), 2) walking and crossing over an obstacle with height set at 10% of body height (OC), 3) sitting and performing a 3-back test, in which participants listened a series of digits over a loud speaker and were instructed to verbally respond “yes” whenever the digit matches the one from three steps earlier in the sequence (Nback), 4) dual-task: WALK+Nback, and 5) dual-task: OC+Nback. A 30-minutes sit-to-stand task at a pre-determined pace was employed to induce fatigue as indicated by the participant’s inability to continue or when the movement frequency falling below the pace after the examiner’s encouragement. The maximal voluntary isometric strength of knee extensors was assessed immediately before and after the fatigue protocol and at the completion of the entire study protocol. Whole body motion data were collected from a set of 29 retro-reflective markers placed on bony landmarks with a 12-camera motion system. The whole-body center of mass (CoM) was calculated as the weighted sum of 13 body segments. Gait balance control was examined using the total medial-lateral CoM displacement (M-L CoM), peak CoM medio-lateral velocity (M-L vCoM) and stride width during each of the walking conditions. A crossing stride was defined as the gait cycle during stepping over the obstacle between heel strikes of the trailing foot immediately before and after crossing the obstacle. Gait speeds were calculated as the average forward CoM velocity during a gait cycle. Two separate two-way ANOVAs with repeated measures were used to examine effects of fatigue (pre- and post-fatigue) and task (single- and dual-tasks) in walking and obstacle-crossing conditions. Alpha level was set at .05. RESULTS AND DISCUSSION An average of 11.0% knee extensor strength reduction was observed immediately after the completion of fatigue
protocol, and it was recovered to approximately 5.8% by the completion of study protocol. The average time-to-fatigue during the sit-to-stand task was 23.0 minutes. Gait speed and M-L vCoM showed task main effects during walking. Participants walked slower but demonstrated a faster frontal plane sway when responding concurrent 3-back test than they did under single-task condition. M-L vCoM showed a tendency toward a significant interaction effect, p=.067, η2
p = .45 (Figure 1). No significant effects were detected for M-L CoM or stride width. Gait speed remained unchanged after fatigue during obstacle-crossing. M-L vCoM demonstrated a significant interaction effect (Figure 1). Participants swayed faster post-fatigue during the single-task obstacle crossing. However, when a concurrent cognitive demand was imposed, a slower frontal plane sway was observed. No fatigue main effects were found in M-L CoM, stride width, and crossing behaviors.
Figure 1. Peak medio-lateral velocity of center of mass. CONCLUSIONS Older workers demonstrated a faster sway in single- but a slower sway in dual-task obstacle crossing. This might be a result of that older adults prioritize gait balance over cognitive task performance. The central nervous system might anticipate that balance control would be disturbed after fatigue and, therefore, prioritize the effort to maintain dynamic balance during the dual-task obstacle-crossing condition. The peak CoM medio-lateral velocity could be a sensitive measurement and applied in occupational medicine to monitor fatigue status in older workers. More study participants are necessary to strengthen the current findings. REFERENCES 1. Hortobágyi T et al. J Gerontol A 58, M453–60, 2003. 2. Parijat P & Lockhart TE. Ergonomics 51, 1873–84,
2008. 3. Lorist MM et al. The Journal of Physiology 545, 313-9,
2002.
AN INITIAL LOOK AT GAIT STABILITY DURING OVER-GROUND WALKING IN CANCER PATIENTS
1Patrick D. Fischer, 1Scott M. Monfort, 2Maryam B. Lustberg, and 2Ajit M.W. Chaudhari
1Montana State University, Bozeman, MT, USA; 2The Ohio State University, Columbus, OH, USA
email: [email protected] website: http://www.montana.edu/biomechanics/
INTRODUCTION
Cancer survivors are reported to be at an increased risk of
falling [1], but little is known about the factors that drive this
problem. Many falls occur during gait, suggesting that altered
locomotion is an important consideration that needs better
characterization in this population. One method of
characterizing gait is through Lyapunov exponents, which
quantifies local stability [2]. Altered spatiotemporal gait
characteristics in cancer patients who received chemotherapy
have been reported by us and others [3]. However, to our
knowledge, gait stability measures have not been utilized to
quantify gait impairments in this population.
The purpose of this pilot study was to investigate the effects
of chemotherapy on local stability during over-ground
walking. The primary hypothesis was that patients receiving
chemotherapy would exhibit decreased local stability when
compared to a cancer control group.
METHODS
Seventeen cancer patients participated in the study after
providing IRB-approved informed consent and were divided
into two groups: a control group having undergone no
chemotherapy (f/m: 6/0; 59.3±9.7yr) and a group that received
taxane- or oxaliplatin-based chemotherapy (f/m=9/2;
49.3±11.4yr). Participants completed validated patient-
reported outcomes (PROs) including EORTC QLQ-C30 [4].
Participants were asked to walk at a self-selected speed
around an indoor track; no additional task was required.
Inertial measurement units (IMUs, IMeasureU) were attached
to the L5 region of the lower back and the left ankle. Triaxial
accelerometer and gyroscope data were recorded at a
sampling rate of 500 Hz for the duration of a single trial.
A state space consisting of pelvis 3D linear accelerations and
angular velocities with a single time delay copy was
constructed from the collected data [3]. 150 consecutive
strides were considered from each trial, and each trial was
normalized to 15,000 data points. The maximum short-term
(SLE) and long-term (LLE) Lyapunov exponents were
calculated as measures of local stability [2], with greater
values indicating decreased local stability.
Independent 2-sample t-tests and Wilcoxon Rank Sum tests
were performed to identify differences for group
demographics and PROs, respectively. Best subsets
regression analyses were used to identify linear regression
models that best explained the variance in Lyapunov
exponents. Model performance was evaluated using adjusted-
R2 and Mallow’s Cp values. Significance was set at p<0.05.
RESULTS AND DISCUSSION
Patients who were treated with chemotherapy reported greater
symptom severity compared to the control group (Table 1).
Table 1. Group demographics and select characteristics.
Patient
Characteristic
Control
Group
Chemotherapy
Group p-value
Age 59.3 ± 9.7 49.3 ± 11.4 0.079
Quality of Life a 6.25 ± 0.69 5.00 ± 0.81 0.008
Physical
Function b 1.03 ± 0.08 1.67 ± 0.61 0.009
a EORTC QLQ-C30 global health score (1-8: lower=worse) b EORTC QLQ-C30 symptom subscale (1-4: higher=worse)
The best subsets analysis suggested that a model containing
chemotherapy treatment and age best explained SLE. This
model (R2=47%, p=0.011) suggested that chemotherapy
(βchemo=-0.073, p=0.034) was associated with improved local
stability even after controlling for age (βage=-0.002, p=0.19)
and average walking speed in the model (model: R2=47%,
p=0.035; βchemo=-0.073, p=0.048). No other model
coefficients were significant.
One possible explanation is the presence of some internal
compensation exhibited by the group who received
chemotherapy. We speculate that the increased perception of
chemotherapy-related symptoms (Table 1) may be associated
with a more conscious gait strategy. Increased cognitive
attention may enable improved local stability during single-
task gait, but could be potentially hazardous during distracted
gait where this strategy would be hindered. Because of the
small sample size, no definitive conclusion between
chemotherapy treatment and local gait stability may be drawn.
However, further investigation is warranted, and investigating
dual tasks during over-ground walking may provide better
insight into this effect.
REFERENCES
1. Bao et al. Breast Cancer Res Treat, 159: 327-333, 2016
2. Bruijn et al. Annals Biomed Eng, 38(8): 2588-2593, 2010
3. Monfort et al. Breast Cancer Res Treat, 164: 1: 69-77, 2017
4. Aaronson et al. J Natl Cancer Inst, 85(5): 365-376, 1993
ACKNOWLEDGEMENTS
We would like to thank the study participants for donating
their time, and our funding sources: NCI R03 CA182165-01;
NSF GRF DGE-1343
CENTER OF MASS MOTION DURING SIT-TO-STAND CHANGES THROUGH PREGNANCY
Sandra Alejandre-Rios and Robert D. Catena
Gait and Posture Biomechanics Lab, Washington State University, Pullman, WA USA
email: [email protected], web: http://labs.wsu.edu/biomechanics/
INTRODUCTION
Understanding physiological and balance related
performance changes through pregnancy are crucial since
falls are one of the main causes of injury during pregnancy
[1]. Both joint kinematics and kinetics have been found to
change during sit-to-stand (STS) motions. Trunk flexion
becomes a more difficult task because of abdominal volume
increases, especially in the third trimester [2]. Consequently,
pregnant women shift from greater hip flexion moments in the
1st trimester of pregnancy to greater knee flexion moments in
the 3rd trimester [2]. However, these previous studies have
eluded to the STS being a symmetric action through
pregnancy without investigating movement outside of the
sagittal plane.
In this current study, we examined how that center of mass
(COM) motion changes in the STS over the course pregnancy.
We were particularly interested in asymmetric lateral COM
motions since these could indicate inefficient energy
expenditure, the potential for loss of balance during STS, and
a potential for increases in low-back injury.
METHODS
We have currently completed analysis of 5 women tested five
times in 4-week intervals from 16 to 36 weeks gestation.
Participants had body anthropometry measured to determine
the individual masses of 13 body segments [3]. They then had
54 reflective markers placed on the body and performed a
quite standing trial and a laying trial with markers tracked by
a 10-camera motion capture system (MotionAnalysis Corp)
to allow us to calculate COM locations of the 13 body
segments [4]. In between standing and laying trials, they
performed STS at a self-selected pace using a 45 cm height
chair on a force plate.
All markers were tracked at 100 Hz and filtered with a 6 Hz
4th order low-pass Butterworth filter. The body COM was
calculated from the weighted-sum of the 13 body segments
throughout the STS trial. Seven STS cycles for each testing
were split into 2 phases, before (STS1) and after (STS2) the
moment of seat-off. The average times to complete each
phase were measured as dependent variables. The COM
linear ranges of motion and peak velocities in three
orthogonal directions were used as dependent variables. We
also calculated the average coefficient of variation (COV) in
lateral motion during each phase. Four-week intervals of
gestation were used as the independent variable. Dependent
variable change over time was measured with a repeated-
measures general linear model analysis, and follow-up
pairwise comparisons with Bonferroni adjustments (alpha =
0.05).
RESULTS AND DISCUSSION
Time to complete STS1 significantly increased from the 1st
to 3rd testing. The lateral COM range of motion and peak
velocity increased from the 1st to 4th testing. In contrast, the
anterior COM motion decreased from the 3rd testing to the
5th testing. In fact, all motions and velocities appear to
decrease at the last testing.
STS2 also took longer from 1st to 3rd testing and increased
again in the last test. Lateral COM motion (range and COV)
in STS2 displayed a similar pattern as STS1: they increased
to the 4th testing, and then decreased in the 5th testing.
Vertical velocity in rising from the chair followed this same
pattern over time.
There appears to be two changes during pregnancy. First, up
to the start of the third trimester (4th testing), participants
shifted from symmetric forward motion to a lateral
asymmetric rocking motion to initiate standing. We believe
that the change in strategy was adopted to provide sufficient
momentum to push off the chair as volume of torso increased.
Since the pregnant torso precludes enough trunk flexion,
lateral rocking with limited trunk flexion creates enough
forward momentum to rise from a chair later in pregnancy.
Therefore, the adoption of a lateral COM rocking motion may
be dependent on abdomen size, as not all women have similar
abdominal change during pregnancy.
The second, reduced motion in the 5th testing corresponds
with the time point of largest mass. We believe that at this
time point, strength is particularly relied upon to complete the
STS. However, it is not clear why individuals would shift
away from the rocking motion adopted in the 3rd and 4th
testing. Lateral rocking seems like an appropriate alternative
to generate assisting momentum even in the later stages of
pregnancy. Perhaps lateral rocking became insufficient and a
new method not analyzed here was adopted. This current
analysis cannot discount a strategy shift that may include
increased arm counter-reciprocal motions or hands pushing
against the distal thighs to aid in propelling the body COM
forward without relying merely on generating torso
momentum. Our ongoing analyses will include a look at arm
motions that correspond with our COM results.
CONCLUSIONS
Our results provide new perspectives on adaptation of the
STS through pregnancy. However, these performance
adaptations have the potential to increase fall risk or
development of low back pain. Our findings clearly point out
that the STS is increasingly asymmetric during pregnancy,
and as such, future studies should consider the 3D nature
during analyses.
REFERENCES
1. Dunning et al. Maternal Child Health J., 2010.
2. Lou et al. Clinical Biomechanics, 2001.
3. Pavol et al. J Biomechanics, 2002.
4. Catena et al. J. Biomechanics, in press.
ACKNOWLEDGEMENTS
Thanks to Kathryn Lober, Hallie Music, Lexi Fredrickson,
and Daniel Flores in data collection and processing.
INFLUENCE OF VISION ON BALANCE CONTROL DURING CONTINUOUS CIRCULAR PERTURBATIONS
Tomomi Yamamoto1,2, Vicki Komisar1, Brigitte Potvin1, Stephen Robinovitch1 1Injury Prevention & Mobility Laboratory, Dept. of Biomedical Physiology and Kinesiology, Simon Fraser University, Canada
2Mechanical Dynamics and Mechatronics Lab, Dept. of Engineering, Tottori University, Tottori, Japan
email: [email protected], web: http://www.sfu.ca/tips/tips-home.html
INTRODUCTION
Maintaining and recovering balance following postural
perturbations is crucial for avoiding falls. Vision loss impacts
balance control during quiet stance and following sudden,
transient perturbations [1,2]. However, the influence of vision
on balance control during continuous, multi-directional
perturbations, such as those experienced when standing on
moving vehicles, is less understood. In this preliminary study,
we explored how vision affects the ability of young adults to
control balance (tendency to step) during continuous, circular
perturbations, with the longer-term goal of using this
paradigm to improve our understanding of how balance is
affected by aging, disease and learning.
METHODS
Participants (n=3) stood on a crash pad mounted to a robotic
platform, which translated circularly (radius=10cm) in the
horizontal plane to deliver a destabilizing centripetal force.
During the trials, the angular velocity of the platform
increased from 0 to 6 rad/s with an acceleration of 0.15, 0.25
or 0.5 rad/s2 (LOW, MED and HIGH). Participants were tested
while looking at a fixed target on the wall (VISION), and while
blindfolded (NO-VISION). The protocol involved 13 trials: a
‘practice’ trial (VISION, MED) to learn the protocol (not
analyzed), followed by two trials for each visual condition
and acceleration combination. Participants were instructed to
“maintain balance and avoid stepping”.
Balance control was evaluated based on whether participants
stepped, and the platform velocity at step initiation
(determined from analysis of motion capture markers
(Qualisys MIQUS) on the crash pad). Stepping was defined
by upward displacement of 10 cm or more of motion capture
markers on the lateral malleoli, and confirmed by video
inspection.
RESULTS AND DISCUSSION
Without vision, participants were more likely to step or fall
Stepping occurred in every NO-VISION trial, and in 56% of
VISION trials. Further, participants fell in 17% of NO-VISION
trials, versus 0% of VISION trials. For VISION trials, steps were
more common at higher accelerations (occurring in 33% of
VISION-LOW trials, 50% of VISION-MED trials and 83% of
VISION-HIGH trials).
Without vision, stepping was initiated at lower platform
velocities
Steps tended to occur at higher angular velocities in VISION
than NO-VISION trials, for all accelerations (Fig. 1). Further,
for LOW and MED perturbations, steps were more frequently
initiated when the platform moved anteriorly (resulting in
backward falling) (Fig. 2). For HIGH perturbations, stepping
was initiated more often when the platform moved laterally
or posteriorly (Fig 2). This suggests that participants may
have used different strategies to control balance at different
accelerations (e.g., leaning forward at high acceleration).
Figure 1: Platform velocity at which stepping was initiated
for each perturbation and visual condition. The bars show
mean + 1 standard deviation.
Figure 2: a) Platform velocity and position when steps were
initiated. Each point represents a distinct trial for each test
condition. The platform started at 0o and translated clockwise.
Radial distance from the centre signifies platform velocity
(rad/s); angular position on the outside circle signifies
displacement from start (o). b) Participant orientation on the
platform with respect to the direction of platform movement.
CONCLUSIONS
Our pilot results suggest that perturbation velocity thresholds
for step initiation are reduced in the absence of vision –
implying increased challenge of standing balance control.
Furthermore, acceleration magnitudes influenced both
tendency to step, and the direction of platform movement at
the instant of stepping. Ongoing work is examining, with a
larger sample, how step thresholds, and transition between
ankle and hip strategies for standing balance, depend on
vision and surface stiffness; how predictive strategies for
balance control emerge through increased exposure to
continuous circular perturbations; and how effects of training
transfer across different types of perturbations.
REFERENCES
1. Rogers MW, et al. Exp Brain Res 136, 514-522, 2000
2. Martinelli A, et al., Exp Brain Res 233, 1399-1408, 2015
ACKNOWLEDGEMENTS
Funded by grants from the AGE-WELL Core Research
Program (AW CRP 2015-WP5.2) and the Canadian Institutes
for Health Research (TEI-138295).
0
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Vision – HIGH
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a)
0o
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b)
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