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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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