Postural Responses in Various Bases of Support and Visual...
Transcript of Postural Responses in Various Bases of Support and Visual...
International Journal of Sport and Exercise Science, 1(4):87-92 87
Postural Responses in Various Bases of Support and Visual
Conditions in the Subjects with Functional
Ankle Instability
Yi-Wen Chang 1, Hong-Wen Wu
2, Wei Hung
1,*, Yen-Chen Chiu
1
1 Department of Exercise and Health Science, National Taiwan College of Physical Education, Taichung, Taiwa, ROC 2Department of Physical Education, National Taiwan College of Physical Education, Taichung, Taiwan, ROC
Received 23 Aug 2009; Accepted 25 Nov 2009
Abstract
Ankle sprain is one of the most common injures in sports. The purpose of this study was to investigate the effects of
base of support and vision on standing balance in healthy subjects and the subjects with functional ankle instability. Six
healthy subjects and six subjects with functional ankle instability were recruited. Centre of pressure length was
measured with a balance plate during standing in four different bases of support, standing with feet shoulder’s width
apart, standing with feet together, tandem standing and single-limb standing, and in two visual conditions, eyes-open
and eyes-closed. In anterior-posterior direction, base of support and vision may be significant in postural control in the
subjects with functional ankle instability but not in normal group. Stance with feet shoulder’s width apart, stance with
feet together, and eyes-open, showed lesser centre of pressure length in static standing. In dynamic standing, change of
bases of support would be significant in the stable and unstable ankles. In medial-lateral direction, effects of base of
support and vision could be more concern in static standing but not in dynamic standing. Understanding these two
important human factors in stable and unstable ankles would be beneficial in developing effective intervention
strategies targeting specific populations.
Keywords: Postural sway, Standing balance, Ankle sprain, Sports injury
Introduction
Ankle sprain is arguably one of the most common injures in
sports. It was estimated that 14% - 17% of all sport injuries
were ankle sprain [1]. Eighty-five percent of ankle sprains
were inversion injuries, predisposing to the second injury after
the first episode [2]. Recurrent ankle sprain can lead to
considerable impairment characterized by functional ankle
instability. Functional ankle instability is defined as a feeling
or a tendency of giving way in the ankle joint. An
epidemiological study investigating in Hong Kong athletes
showed that as much 73% of all athletes had recurrent ankle
sprains and 59% of these injured athletes had significant
disability, resulting in limitation to their athletic performance
[3].
The force plateform or stabilometry to quantify the postural
sway has been widely used to evaluate the standing balance
[4-6]. The ability to maintain a good stance balance would
* Corresponding author : Wei-Hung
Tel: +886-4-2221-3135 Ext 1303
Fax: +886-4-2225-8026
Email:[email protected]
be identified if the centre of pressure (COP) showed lesser
excursion during body sway. The deficient postural control
with a history of inversion ankle sprain has been demonstrated
since the postural sway in stance substantially increased in
athletes with multiple ankle sprains [7-9].
Three possible contributing factors underlying the ankle
with functional instability are proprioceptive disorder, muscle
weakness and ligamentous laxity. Lentell et al. (1995) found
that impairment in passive movement sense was more
concerns than strength insufficiency when treating the ankle
with functional instability [10]. Also, greater ankle joint
repositioning errors have been found in the subjects with
functional instability [8,11]. Mitchell et al. (2008) revealed
postural sway deficits in functional ankle instability and a
significant relationship between reaction time in peroneals and
postural sway in unstable ankle [12].
In addition to the potential pathological factors, base of
support and vision, the alterations on sensory inputs in the
body, are two of the most important factors affecting the
postural response. There were several researches addressing
the postural sway change with or without vision in the
International Journal of Sport and Exercise Science, Vol. 1. No.4 2009 88
gymnastics [13], in the subjects with functional instability [12],
and in the elderly [14-15]. There was one research exhibiting
the postural sway in different body lean angles [16]. However,
there was very limited report simultaneously considering the
effects of base of support and vision on standing stability.
Therefore, the purpose of this study was to investigate the
effects of base of support and vision on standing balance in
healthy subjects and the subjects with functional ankle
instability.
Methods
Twelve male subjects participated in this study. They had a
mean age of 21 years (range 18 – 22), a mean body weight of
71 kg (range, 63 – 82), and a mean height of 174 cm (range,
167 – 185). Subjects were recruited for two groups, including
six normal healthy subjects and six subjects with functional
ankle instability. The definition of functional instability has
widened to include the occurrence of recurrent joint instability
and the sensation of joint instability due to the contributions of
any neuromuscular deficits [17]. The criteria for the subjects
with functional ankle instability in this study were adopted
from Kaminski’s [18] and Fu’s studies [8], including that (1)
they have been experienced unilateral ankle sprain at lease
twice in two years; (2) there was a giving way sense or
unstable feeling on the sprained ankle; (3) there was no
structural instability during anterior drawer test; and (4) they
have not suffered unilateral ankle sprain (grade II) in recent
three months. The anterior drawer test was performed by an
experienced athletic trainer. Participants were screened to
ensure that except unilateral unstable ankle, they did not have
any other disorder that might affect standing tasks employed in
this study. Anyone with any surgical history in lower extremity
was excluded in this study. There was no pain or any other
uncomfortable symptoms in the unstable ankle for the subjects
with functional ankle instability in the testing day. The
experimental protocol has been approved by the committee of
National Taiwan College of Physical Education, Taiwan.
Research purpose and experimental protocol have been
completely explained and the informed consent was signed for
each subject.
Centre of pressure (COP) length in body sway was
measured with a balance plate (DigiMax system, MechqTronic,
Hamm). Subjects were asked to perform standing in four
different bases of support, including standing with feet
shoulder’s width apart, standing with feet together, tandem
standing and single-limb standing. In single-limb standing,
right leg was tested for normal group and the leg with unstable
ankle was tested for instability group. Two different visual
conditions were tested, eyes-open and eyes-closed. Static and
dynamic standings were considered in this study. There was a
20-sec data collection in static standing, in which there was no
active movement on balance plate. There was a 10-sec data
collection in dynamic standing, in which there was a sudden
perturbation in frontal plane. The balance plate was locked
with a 20-mm lateral displacement and the lock was suddenly
released at the third second of data collection without prior
announcement to the subjects. The subjects were required to
keep stable stance as much as he could in all testing conditions.
The testing order was completely random for each subject.
COP trajectory data in medial-lateral direction and
anterior-posterior direction were measured. Two-factorial
ANOVA with repeated measures (4 base of support x 2 vision)
was used for statistical analysis (SPSS, V13.0). P value less
than 0.05 was considered statistically significant.
Results
Typical COP trajectories in static and dynamic standings
were shown in Figure 1. Lengths of COP in different bases of
support and visual conditions in static standing were shown in
Table 1. For the COP lengths in medial-lateral direction,
significant differences in base of support and visual factors
were found both in normal and instability groups (p<0.05).
Standing with eyes-open showed shorter COP length than
eyes-closed, indicating vision demonstrated substantial
importance on static standing balance. In pairwise comparison
between four bases of support, tandem standing and
single-limb standing showed greater COP lengths than the
standings with feet shoulder’s width apart and feet together. It
was implied that the width of the supporting base played a
critical role in static standing in stable ankles as well as
unstable ankles.
Table 1. COP lengths (mm) in static standing in instability and normal groups.
Eyes-Open Eyes-Closed
BOS1 BOS2 BOS3 BOS4 BOS1 BOS2 BOS3 BOS4
ML Instability*† 10±7 14±5 46±25 94±76 20±7 26±11 230±210 615±557
Normal*† 6±7 12.9±7 29±12 72±45 5±4 17±2 155±63 442±476
AP Instability*† 11±3 19±1 24±2 71±77 22±11 23±5 86±53 395±404
Normal 14±3 18±3 19±0 52±43 14±4 18±3 52±23 322±412
ML = medial-lateral direction; AP = anterior-posterior direction; BOS1 = feet shoulder’s width apart; BOS2 = feet together; BOS3 = tandem
standing; BOS4 = single-limb standing. Significant difference in base of support factor* and visual factor† (repeated measure ANOVA, p<.05)
In anterior-posterior direction, significant effects on the
factors of base of support and vision were found in instability
group during static stance (p<0.05). However, there was no
significant difference in normal group. For the subjects with
functional ankle instability, changes of base of support and
vision showed substantial influence on postural response in
anterior-posterior direction during static stance.
International Journal of Sport and Exercise Science, 1(4):87-92 89
(a) (b)
Figure 1. COP trajectories in static standing (a) and dynamic standing (b). (horizontal axis: medial-lateral direction; vertical axis:
anterior-posterior direction)
Lengths of COP in different bases of support and visual
conditions in dynamic standing were shown in Table 2. In
medial-lateral direction, there was no significant difference
between different bases of support and visual conditions in
normal and instability groups. In anterior-posterior direction,
however, there was a significant difference between different
bases of support in normal group as well as instability group
(p<0.05). No significant difference between different visual
conditions was found in dynamic standing.
Table 2. COP lengths (mm) in dynamic standing in instability and normal groups.
Eyes-Open Eyes-Closed
BOS1 BOS2 BOS3 BOS4 BOS1 BOS2 BOS3 BOS4
ML Instability 161±37 177±40 275±190 262±125 161±41 218±104 268±260 396±213
Normal 140±48 127±40 244±230 168.1±83 153±25 147±71 191±87 248±147
AP Instability* 39±6 41±10 74±34 86±45 43±14 60±25 78±43 153±70
Normal* 31±21 21±6 56±32 55±15 28±13 42±26 62±26 117±74
ML = medial-lateral direction; AP = anterior-posterior direction; BOS1 = feet shoulder’s width apart; BOS2 = feet together; BOS3 = tandem
standing; BOS4 = single-limb standing. Significant difference in base of support factor* (repeated measure ANOVA, p<.05)
Discussion
This study revealed how these two important human factors,
base of support and vision, attributed to standing balance in
normal subjects and the subjects with functional ankle
instability. It was found that the COP length was increased
with the decreasing base of support in normal and instability
groups. Although there are the same supporting areas in
tandem standing and standing with feet together, there was a
greater COP length in tandem position whose medial-lateral
width is much narrower, indicating the change of base of
support in medial-lateral direction is more significant in
postural control than in anterior-posterior direction.
Santos et al. (2009) studied the electromyography activities
of trunk and leg muscles and ground reaction in anticipatory
postural adjustments in stances with feet shoulder width apart,
and with feet together and single-limb stance during lateral
perturbations of postural instability [19]. Smaller anticipatory
postural adjustments in lateral muscles were found in a wider
base of support, with feet shoulder width apart, and with feet
together. Although their measured variables were different
from our study, their finding was consistent with our results
that the COP lengths in anterior-posterior direction in dynamic
standing were smaller in a wider base of support, with feet
shoulder width apart, and with feet together, than narrower
ones, the tandem stance and single-limb stance. This
information allows us to more understand how important the
influence of base of support in subjects with functional ankle
instability, so as to develop effective intervention strategies for
recurrent ankle sprain.
Mitchell et al. (2008) found that stable ankle and unstable
ankle had similar postural control with vision but unstable
ankle showed greater anteroposterior postural sway than the
healthy ankle [12]. Brown et al. (2009) used tibial nerve
stimulation as a perturbation to assess the balance deficits in
athletes with functional ankle instability and found that time to
stabilization in the anterior-posterior direction was
significantly different between healthy and instability groups,
in which longer time to return to a stable range of ground
reaction force was found [20]. There was a good agreement
with our findings that significant effects of vision and base of
support in static standing were found in anterior-posterior
direction in instability group but not found in normal group.
Inversion sprain was the ankle injury in the medial-lateral
direction. However, postural response in anterior-posterior
International Journal of Sport and Exercise Science, Vol. 1. No.4 2009 90
direction, quantified by COP length or time to stabilization,
seems to be concerned in the subjects with functional ankle
instability. Clinically the findings suggest the utilization of a
battery of task to identify the overall postural performance.
Docherty et al. (2006) investigated the postural control deficits
in subjects with functional ankle instability by the balance
error scoring system, traditionally used for monitoring
recovery from mild head injury [21]. More errors, implying
poorer balance, were found in the subjects with functional
ankle instability on tandem stancefoam, single stancefirm and
single stancefoam conditions. Considering the effect of
perturbation, there were similar findings despite different
scoring parameters and perturbations were used between our
study and Docherty’s. In medial-lateral direction, that
single-limb stance and tandem stance showed greater COP
trajectories than feet together and feet apart was only found in
static standing, but not in dynamic standing, possibly because
the perturbation, mainly generated in medial-lateral direction,
was so enormous to diminish any effect from the change of
base of support or vision.
In summary, our findings suggest that, in anterior-posterior
direction, base of support and vision may be important factors
in postural control in athletes with postural deficit following
recurrent ankle sprains. Three conditions, stance with feet
shoulder width apart, stance with feet together, and eyes-open,
showed better postural control in static standing. However, no
significance in anterior-posterior direction was found in the
subjects with stable ankles. In dynamic standing with sudden
perturbation, change of bases of support would be more
important than visual effect in the subjects with stable and
unstable ankles, implying postural responses in
anterior-posterior direction with vision and without vision
were similar in dynamic standing. In medial-lateral direction,
base of support and vision could be more concerned in static
standing but not in dynamic standing, no matter how ankle is
unstable or not. Understanding these two important human
factors, bases of support and vision, in stable and unstable
ankles would be very useful in developing effective
intervention strategies targeting specific populations.
Acknowledgments
This study was supported by the grant of National Taiwan
College of Physical Education (97DG0011), Taichung, Taiwan.
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