Research in Developmental Disabilities 34 (2013) 198–206

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Research in Developmental Disabilities

Adolescents with intellectual disability have reduced postural balanceand muscle performance in trunk and lower limbs compared to peerswithout intellectual disability

Sven Blomqvist a,*, Josefine Olsson b, Louise Wallin b, Anita Wester c, Borje Rehn b

a Swedish Development Center for Disability Sport, Box 1002, SE-821 11 Bollnas, Swedenb Department of Community Medicine and Rehabilitation, Physiotherapy, Umea University, 901 87 Umea, Swedenc Department of Research and Evaluation, Swedish National Agency for Education, 106 20 Stockholm, Sweden

A R T I C L E I N F O

Article history:

Received 30 May 2012

Received in revised form 9 July 2012

Accepted 9 July 2012

Available online 31 August 2012

Keywords:

Young adults

Postural control

Mental retardation

A B S T R A C T

For adolescent people with ID, falls are more common compared to peers without ID.

However, postural balance among this group is not thoroughly investigated. The aim of

this study was to compare balance and muscle performance among adolescents aged

between 16 and 20 years with a mild to moderate intellectual disability (ID) to age-

matched adolescents without ID. A secondary purpose was to investigate the influence of

vision, strength, height and Body Mass Index (BMI) on balance. A group of 100 adolescents

with ID and a control group of 155 adolescents without ID were investigated with five

balance tests and three strength tests: timed up and go test, one leg stance, dynamic one

leg stance, modified functional reach test, force platform test, counter movement jump,

sit-ups, and Biering-Sørensen trunk extensor endurance test. The results showed that

adolescents with an ID in general had significantly lower scores in the balance and muscle

performance tests. The group with ID did not have a more visually dominated postural

control compared to the group without ID. Height, BMI or muscle performance had no

strong correlations with balance performance. It appears as if measures to improve

balance and strength are required already at a young age for people with an ID.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Individuals with intellectual disability (ID) show: a high prevalence of obesity (Rimmer & Yamaki, 2006); low level ofphysical activity and performance (Frey & Chow, 2006; Lin et al., 2010); frequently more falls (Chiba et al., 2009; Sherrard,Tonge, & Ozanne-Smith, 2001); and increased health risks (Rimmer & Braddock, 2002) compared to the population ingeneral. Physical activity has a positive effect on obesity, physical performance and health risks factors. It can also improvepostural balance for people with ID with age between 18 and 45 (Guidetti, Franciosi, Gallotta, Emerenziani, & Baldari, 2010).

The postural balance system is complex and requires interaction between musculoskeletal and neural subsystems suchas visual, vestibular, and somatosensory systems (Shumway-Cook & Woollacott, 2001, chapter 7). The somatosensorysystem seems to mature at 3–4 years of age, while the visual and vestibular systems reach adult level at 15–16 years of age(Steindl, Kunz, Schrott-Fischer, & Scholtz, 2006). To fully measure balance ability, several balance tests are required thatinvolve the various subsystems (Horak, Wrisley, & Frank, 2009).

* Corresponding author. Tel.: +46 703 41901; fax: +46 278 24456.

E-mail address: sven.blomqvist@suh.se (S. Blomqvist).

0891-4222/$ – see front matter � 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.ridd.2012.07.008

S. Blomqvist et al. / Research in Developmental Disabilities 34 (2013) 198–206 199

Some studies have measured the balance in individuals with ID and shown a reduced ability compared to the generalpopulation (Dellavia, Pallavera, Orlando, & Sforza, 2009; Hale, Miller, Barach, Skinner, & Gray, 2009; Lahtinen, Rintala, &Malin, 2007; Suomi & Koceja, 1994). However, these studies only measured balance in one single way (one or twosubsystem) and in small populations of elderly people. It would be valuable to investigate if the reduced ability is existentalready at a young age. Recently, falls have been reported to be more common in adolescents with ID compared to their peerswithout ID (Sherrard et al., 2001), which could depend on reduced postural balance. To understand if postural balance isreduced in young individuals with ID, it is necessary to perform tests on a large sample.

During normal conditions, the visual subsystem appears to be the dominant subsystem for postural balance amonghealthy individuals (Shumway-Cook & Woollacott, 2001, chapter 7). Clinical observations from the Swedish DevelopmentCentre for Disability Sport, suggest that adolescents with ID have a more visually dominated postural balance than theirpeers. However, the literature reports contradictory results in adults. Dellavia et al. (2009) found that the ratio between eyes-open and eyes-closed sway was greater for adults without ID than for those with ID (Dellavia et al., 2009), but Suomi andKoceja (1994) found the opposite for a group of adults with ID. Various studies show that a high Body Mass Index (BMI) andheight also can influence postural balance among children, adults and elderly people without ID (Deforche et al., 2009;Duncan, Weiner, Chandler, & Studenski, 1990; Handrigan et al., 2010). Another factor that seems to be important for posturalbalance is leg strength and some studies report a correlation between postural balance, strength and falls in older people(Wiacek et al., 2009; Yokoya, Demura, & Sato, 2008). However, Granacher and Gollhofer (2011) could find no correlationbetween strength and postural balance for young healthy people.

The main purpose of this study was to investigate postural balance among adolescent men and women aged 16–20 yearswith mild to moderate ID, and make comparisons with age-matched adolescents without ID. A secondary purpose was toinvestigate the influence of vision, strength, height and BMI. The hypotheses are that adolescents with ID have reducedpostural balance, strength and a more visually dominated postural balance in comparison with non-ID adolescents.

2. Method

2.1. Recruitment

It was calculated that 80 persons in each group were required to detect a difference in the postural balance test dynamicone-leg stance (DOLS) between groups with an odds ratio of 2.0 (power = 0.80, significance level = 0.05, one-sided test). Twoupper secondary schools in Sweden were contacted, one for adolescents with ID and one for non-ID adolescents. Permissionwas given by the principals of the two schools for a visit to all classes to provide information about the study. All students,both ID and non-ID, received verbal and written information about the study and was asked to participate. A letter was senthome to the guardians of the students with ID younger than 18 years old. The letter contained information about the studyand a request to return a signed approval form allowing their son/daughter to participate. Only students whose guardiansreturned the approval form were allowed to take part (Fig. 1).

2.2. Participants

Adolescents in the age range 16–20 years were included. A group of 100 adolescents with ID, both men and women,volunteered to participate (ID-group). The control group included 155 adolescents, both men and women, without ID(Table 1). All adolescents who volunteered to do so were allowed to participate in the study. The ID-group had asignificantly higher mean BMI and the height for women was significantly lower than for non-ID women.

All participants in the ID group had been administratively defined as having a mild to moderate ID (IQ 70–35) by means ofan intellectual functioning test (IQ-test) and standardized tests to determine limitations in adaptive behaviour in threeskills; conceptual, social and practical. Those tests were carried out by a registered psychologist.

Exclusion criteria for both groups were; sensory deficits in lower extremities (loss of sensibility, affected stretch reflexesor reduced strength in lower extremities), recent injury to lower extremities, impaired vision (visual acuity value >0.10),history of or ongoing vestibular neuritis, illness in the few days preceding the tests, a diagnosis of cerebral palsy and use ofwalking aids.

2.3. Test procedure

An interview was done with each participant concerning exclusion criteria followed by screening for any loss of sensoryfunction. Age, height and weight of each student were measured. Vision test was carried out by using an eye chart. A batteryof five postural balance tests (two static and three dynamic) and three muscle strength tests was used (Blomqvist, Wester,Sundelin, & Rehn, 2011). The postural balance tests were performed before the muscle performance tests and in analternating order to avoid any systematic bias. The strength tests were however, performed in the same order each time. Alltests were performed barefoot. There was no trial run and all participants were allowed three attempts, with a 30 s restbetween each, at all tests. There were six different test leaders during the test period, two were experiencedphysiotherapists, and four physiotherapy students. All test leaders were trained and educated by one of the physiotherapistswho was also a test leader. The training and education included practical performance of and discussion about the tests.

Written and verbal

information

ID non-ID

280 520

Interest

ID non- ID

142 269

Tested

ID no n-ID

102 157

Cancel latio ns

ID no n-ID

40 112

Total ID

n=100

Total non-ID

n=155

Exclu ded

ID no n-ID

2 2

Fig. 1. Sample selection procedure for the ID-group and the non-ID group.

S. Blomqvist et al. / Research in Developmental Disabilities 34 (2013) 198–206200

2.4. Postural balance tests

Several postural balance tests were used to test different aspects of postural balance ability.

2.4.1. Expanded timed up and go test (ETUGT)

This test evaluates the subject’s dynamic postural balance, and a faster performance indicates a better dynamic posturalbalance. Standardized instructions given to the participants were to perform the test as fast and safely as possible, but not torun. The subject’s performed the test three times and the fastest time was recorded (Wall, Bell, Campbell, & Davis, 2000).

2.4.2. Modified functional reach test (M-FRT)

This test measured how far a person was able to reach forward without losing postural balance, i.e. moving the feet orfalling, and it evaluates the ability to move the centre of mass within the limits of stability. The test was modified in such away that it was performed with a stand/tripod with a sliding adjustable plate, as people with ID find it difficult to understandhow to perform the original test. The subject was instructed to lean forward as far as possible without losing posturalbalance, and with both arms pushing the plate forward. The push-length was measured in centimetres. Each subjectperformed the test three times and the best result was recorded (Blomqvist et al., 2011).

Table 1

Overview of the subjects with regard to age and anthropometric characteristics, stratified in men and women.

N Age (SD) Weight (SD) (kg) p-Value weight Height (SD) (m) p-Value height BMI (SD) (kg/m2) p-Value BMI

Men

ID 60 17.9 (1.1) 73.2 (15.7) 0.813 1.79 (.07) 0.360 22.7 (4.1) 0.588

Non-ID 67 17.2 (1.0) 72.6 (11.5) 1.80 (.07) 22.4 (3.3)

Women

ID 40 18.0 (1.3) 68.5 (17.2) 0.102 1.65 (.08) 0.037 25.0 (5.6) 0.014

Non-ID 88 17.2 (1.0) 63.5 (10.7) 1.68 (.06) 22.5 (3.6)

Total

ID 100 17.9 (1.2) 71.3 (16.4) 0.045 1.74 (.10) 0.846 23.6 (4.9) 0.038

Non-ID 155 17.2 (1.0) 67.5 (11.9) 1.73 (.09) 22.5 (3.5)

BMI, weight (kg)/height2 (m); ID, subject with intellectual disability; non-ID, subject without intellectual disability; r, value of correlation; and p, value o

significance. Significance level was set to a p-value of less than 5%.

f

S. Blomqvist et al. / Research in Developmental Disabilities 34 (2013) 198–206 201

2.4.3. Dynamic one-leg stance (DOLS)

DOLS evaluates aspects of dynamic and static postural balance. The test has five levels of difficulty, with level one beingthe lowest and level five the highest. Each level was scored with one point (level one gave one point, etc.) and a higher levelwas considered more challenging for postural balance. If the subject moved the supporting foot from its original positionduring the test, the attempt was stopped. It was also not permitted to hook the free leg round the supporting leg. The subjecthad three attempts at each level, and if he/she completed one level satisfactorily he/she proceeded to the next level. Theparticipants were tested for both left and right leg and also with eyes open (EO) and blindfolded (BF). For more informationon DOLS, see Blomqvist et al. (2011).

2.4.4. One-leg stance (OLS)

This test evaluates the subject’s static postural balance. The subject was asked to stand on one leg with arms hanging attheir side for as long as possible up to a maximum of 30 s. The instructions to the subject were to stand on one leg as still andrelaxed as possible. The participants were tested for both left and right leg and also with EO and BF. The best of threeattempts was recorded (Bohannon, 1994).

2.4.5. Force platform test (FPT)

FPT measured postural sway by detecting the velocity (mm/s) of CoP. Lower sway velocity was considered to reflect betterpostural balance. The subject stood on a force platform (MuscleLab model ET-FPL-01) with arms hanging at their side for amaximum of 30 s while the MuscleLab (Model 4000e) measured the total sway. The subject had to perform three differentactivities; stand with feet together (FT), semi standing (SS) (one foot in front of the other), and one leg stance (left and right).The participants were tested both with EO and BF. The first two activities FT and SS were added to the testing procedure afterinitially 26 participants had been tested. The reason for this was that the one-leg stance alone might conceivably have beentoo difficult for the ID group and would therefore complicate comparisons. The instructions to the participants were to standas still and relaxed as possible. Three attempts on each conditions and the best was recorded (Blomqvist et al., 2011).

2.5. Muscle performance tests

2.5.1. Counter movement jump (CMJ)

This test evaluates maximal jump height which reflects leg-muscle strength, power and coordination. The test wasperformed standing on a box with a belt around the waist. The belt had a string that was connected to a measuring device inthe box called MuscleLab (Model 4000e) and a computer that registered the height of the CMJ in centimetres. Each subjectperformed the test three times, with a short pause between each jump. The best was recorded. Before the actual jump, thesubject was asked to stand on their toes so the actual height of the jump could be calculated (Markovic, Dizdar, Jukic, &Cardinale, 2004).

2.5.2. Sit-ups

This test measures the abdominal muscle endurance, and the subject was asked to perform as many sit-ups as possibleduring 30 s. The subject lay supine on the floor with 908 flexion in the knee joints, hands at the side of their head holding arope that the subject placed behind their head, and with elbows pointing straight forward. To do a correct sit-up the elbowsshould touch the knees and then go back so the shoulders touch the floor. The test leader supported the subject’s feet andknees (van de Vliet et al., 2006).

2.5.3. Biering-Sørensen trunk extensor endurance test (BSTEET)

This test measures endurance in the extensor muscles of the trunk. The subject lay prone on a bench with the lower bodyfixed to the bench, with belts strapped around the ankles, the knee creases and the buttocks. The trunk, from the upperborder of the iliac crest and upwards, hung unsupported beyond the bench. When starting the test the subject was asked toplace their arms across their chest and then maintain the body in a horizontal position, in line with bench, for as long aspossible with the trunk unsupported by the bench. If the subject lowered their upper body they were requested to return tothe horizontal position, and if the subject could no longer maintain the position the test was terminated. The test leader useda stopwatch to measure the time in seconds, and the longer the subject was able to keep the trunk in the required position,the better the endurance of the trunk extensor muscles (Evans, Refshauge, & Adams, 2007; Latimer, Maher, Refshauge, &Colaco, 1999).

2.6. Statistics

To calculate differences in means between the two groups, the independent samples t-test was applied for ETUGT, FRT,FPT velocity, OLS, CMJ, sit-ups and BSTEET. The Mann Whitney U-test was used for comparisons of DOLS since this test usesan ordinal scale. The best of three measures for each test was selected.

To analyze the effects of the removal of visual input, the ratios of sway velocity were computed between pairs ofconditions for the force platform test (FT BF/FT EO, SS BF/SS EO, left leg BF/left leg EO and right leg BF/right leg EO) for bothgroups. Then groups and conditions were compared to see if removal of visual input affected the two groups differently.

Table 2

Mean values (standard deviations, SDs) of the balance and strength tests for young (16–20 years) men and women with and without ID, and the ratio of sway velocity between blindfolded/eyes open for FPT.

Men Women Total Ratio of sway velocity blind-

folded/eyes open for FPT

ID mean (SD)

n = 60

Non-ID

Mean (SD)

n = 67

p-Value ID Mean (SD)

n = 40

Non-ID

Mean (SD)

n = 88

p-Value ID Mean (SD)

n = 100

Non-ID

mean (SD)

n = 155

p-Value ID Non-ID p-Value

TUGT (s)* 12.3 (1.9) 11.4 (1.5) a)66 .002 12.8 (2.0) 11.7 (1.6) .001 12.5 (1.9) 11.6 (1.6) a)153 <.001

FRT (cm)* 37.0 (6.1) 42.5 (5.0) a)66 <.001 34.2 (6.1) 40.5 (4.1) <.001 35.9 (6.2) 41.4 (4.6) <.001

OLS

Left** na na na na na na na na na

Right** na na na na na na na na na

Left BF* 17.9 (9.9) 27.8 (5.2) <.001 19.3 (10.2) 25.8 (7.0) .001 18.5 (10.0) 26.7 (6.3) <.001

Right BF* 20.2 (9.8) 28.6 (3.8) <.001 17.7 (10.9) 26.2 (7.2) <.001 19.2 (10.3) 27.2 (6.1) <.001

FPT (mm/s)*

FT 16.2 (12.3) a)48 11.7 (2.7) .017 12.9 (4.0) a)2 6 11.2 (2.2) .044 15.0 (10.3) a)74) 11.4 (2.5) .004 1.45 1.57 .016

FT BF 21.0 (6.9) a)48 18.6 (5.4) .036 17.6 (5.3) a)26 17.2 (4.3) .730 19.8 (6.6) a)74 17.8 (4.9) .021

SS 28.7 (8.5) a)48 21.3 (4.3) <.001 26.3 (13.7) a)26 21.0 (6.0) .067 27.8 (10.6) a)74 21.2 (5.3) <.001 1.93 1.94 .836

SS BF 52.1 (22.9) a)48 40.8 (13.4) a)66 .003 51.9 (24.3) a)26 40.5 (16.6) .032 52.0 (23.2) a)74 40.6 (15.3) <.001

Left 37.9 (13.5) 28. 2 (4.6) <.001 36.4 (25.0) 25.5 (5.6) .009 37.3 (18.8) 26.6 (5.3) <.001 2.38 2.40 .835

Left BF 90.5 (39.8) 65.9 (21.9) <.001 74.7 (40.9) 61.5 (19.6) .059 84.1 (40.7) 63.3 (20.7) <.001

Right 36.5 (12.9) 26.5 (5.0) <.001 35.5 (23.9) 23.9 (5.3) .005 36.1 (18.0) 25.0 (5.3) <.001 2.41 2.57 .113

Right BF 84.2 (31.9) 67.6 (22.3) .001 79.6 (48.6) 60.9 (17.9) .022 82.4 (39.3) 63.8 (20.1) <.001

CMJ (cm)* 31.3 (6.7) a)59 35.9 (5.1) <.001 19.0 (5.4) a)38 23.9 (5.7) <.001 26.4 (8.6) a)97 29.1 (8.0) .013

Sit ups* 15.8 (5.4) 22.4 (5.5) a)66 <.001 12.8 (5.5) a)39 17.1 (5.2) <.001 14.6 (5.6) a)99 19.3 (5.9) a)154 <.001

BSTEET (s)* 88.8 (45.3) 127.5 (50.2) <.001 81.1 (36.7) a)39 125.8 (55.3) <.001 85.8 (42.0) a)99 126.5 (53.1) <.001

a)nmeans the number of subjects who participated in that test. TUGT, timed up and go test; FRT, functional reach test; OLS, one-leg stance; FPT, force platform test; FT, feet together; SS, semi standing; BF,

blindfolded; CMJ, counter movement jump; BSTEET, Biering-Sørensen trunk extensor endurance test; ID, subject with intellectual disability; non-ID, subject without intellectual disability; and na, not applicable.

* t-Test.

** Mann Whitney U-test. Significance level was set to a p-value of less than 0.003.

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Table 3

Results of dynamic one-leg stance (DOLS) for young (16–20 years) men and women. A score of 1 reflects a lower performance while a score of 5 reflects a

higher performance for DOLS.

Men Women Total

ID (n = 60) Non-ID (n = 67) ID (n = 40) Non-ID (n = 88) ID (n = 100) Non-ID (n = 155)

Median

(min–max)

Median

(min–max)

p-Value* Median

(min–max)

Median

(min–max)

p-Value* Median

(min–max)

Median

(min–max)

p-Value*

DOLS

Left 4 (3–5) 5 (4–5) <.001 4 (1–5) 5 (3–5) <.001 4 (1–5) 5 (3–5) <.001

Right 4 (1–5) 5 (4–5) <.001 4 (1–5) 5 (3–5) <.001 4 (1–5) 5 (3–5) <.001

Left BF 2 (1–5) 3 (2–5) .002 2 (1–4) 3 (1–5) <.001 2 (1–5) 3 (1–5) <.001

Right BF 2 (1–4) 3 (2–5) <.001 2 (1–4) 3 (1–4) <.001 2 (1–4) 3 (1–5) <.001

ID, subject with intellectual disability and non-ID, subject without intellectual disability.

* Mann Whitney U test. Significance level was set to a p-value of less than 5%.

S. Blomqvist et al. / Research in Developmental Disabilities 34 (2013) 198–206 203

The Pearson correlation coefficient was used to calculate correlations between postural balance tests and muscleperformance tests, height and BMI. Spearman’s correlation coefficient was used to calculate correlations when DOLS wasinvolved. The strength of the coefficient was defined as: 0.00–0.25 = little if any correlation; 0.26–0.49 = low correlation;0.50–0.69 = moderate correlation; 0.70–0.89 = high correlation; and 0.90–1.00 = very high correlation (Domholdt, 2000). Thesignificance level was set to a p-value of less than 5%. To avoid mass-significance for analyses of differences in meansbetween groups and correlations, the alpha-value was divided by the number of comparisons (alpha/n) according toBonferroni (for differences in means between groups: 0.05/15 = 0.003 and for correlation analyses: 0.05/21 = 0.002). TheStatistical Package for Social Sciences (SPSS for Windows version 17.0) was used.

2.7. Ethics

The Regional Ethics Review Board in Umea, Sweden, approved the study (No. 09-076M).

3. Results

The non-ID participants (both men and women) achieved statistically significantly better results on all tests, apart fromthe FPT FT with EO and BF. The ratio between BF and EO for FPT conditions was lower for the ID group but not significantly(Table 2). OLS when not BF (left and right) generally showed a ceiling effect and no results are therefore presented.

There were significantly lower scores regarding DOLS for participants with ID compared to the non-ID group, regardingboth right and left leg, with EO and BF (Table 3).

A statistically justified low correlation between height and FRT was observed in both groups (r = 0.35–0.45) (p < 0.001).FRT also had a low correlation with all muscle performance tests for the non-ID group (r = 0.25–0.36) (p < 0.001). ETUGTshowed a low correlation with CMJ and Sit-ups for the ID group (r = 0.32–0.34) (p = 0.001) but not for the non-ID group. OLSleft BF had low correlation with all muscle performance tests apart from CMJ in the ID group (r = 0.26–0.30) (p = 0.001). OLSright BF had a low correlation with CMJ and sit-ups for both groups (r = 0.26–0.39) (p = 0.001). FPT showed no correlationwith the muscle performance tests (Table 4).

4. Discussion

The ID adolescent group as a whole performed less well on the postural balance and muscle performance tests than thenon-ID group, which confirmed our hypothesis. Unexpectedly, the ratio between BF and EO was lower for ID group than tonon-ID group, indicating that adolescents with ID do not have more visual dominance of postural balance compared to theirpeers without ID. Correlations between postural balance test and muscle performance tests, BMI, and height were generallylow.

ETUGT, MFRT, OLS and FPT used in this study have been reported by Blomqvist et al. (2011) to have excellent reliabilityand can be used to evaluate changes over time for adolescents with ID (Blomqvist et al., 2011). We found that all adolescentswith ID could stand on one foot (OLS) for at least 30 s. This was better than the results reported by a Finnish study using theStork test on young (17–22 years) people with ID (Lahtinen et al., 2007). Even if the Stork test and OLS are not done in exactlythe same way, they both measure postural balance while standing on one foot. One reason for the difference could be that inthe Stork test, participants stand on one foot with their hands on their hips and the foot of the free leg resting on the knee ofthe supporting leg, but in OLS, legs and arms are free, which could help the participants control their postural balance.

Suomi and Koceja (1994) investigated the mean lateral sway for 15 s and reported that a group of adults with ID swayedsignificantly more than adults without ID. Dellavia et al. (2009) found that athletes (20–30 years) with ID had a greater meanbody sway than controls without ID. Further, it was reported that the ratio between EO and BF sway area increased more forthe control group than with the ID group (Dellavia et al., 2009), which is in line with the results of the present study.

Table 4

Correlations between the balance test and BMI, height, CMJ, Sit-ups and BSTEET for young (16–20 years) men and women with and without ID.

BMI Height CMJ Sit-ups BSTEET

ID

n = 100

a)n = 74

Non-ID

n = 155

b)n = 154

ID

n = 100

a)n = 74

Non-ID

n = 155

b)n = 154

ID

n = 97

c)n = 71

Non-ID

n = 155

b)n = 154

ID

n = 99

d)n = 73

Non-ID

n = 154

e)n = 153

ID

n = 99

d)n = 73

Non-ID

n = 155

b)n = 154

r p r p r p r p r p r p r p r p r p r p

TUGT (s)* .162 .108 .018b .829 �.003 .977 �.236b .003 �.341 .001 �.171b .034 �.325 .001 �.104e .202 �.283 .005 .003b .973

FRT (cm)* .089 .377 .116 .149 .459 <.001 .340 <.001 .189 .064 .336 <.001 .049 .632 .359 <.001 .137 .176 .252 .002OLS*

Left BF �.039 .702 �.014 .864 �.127 .207 .154 .056 .205 .044 .265 .001 .294 .003 .290 <.001 .300 .003 .296 <.001Right BF �.018 .858 �.052 .519 �.050 .624 .131 .104 .391 <.001 .302 <.001 .334 .001 .261 .001 .277 .006 .177 .028

DOLS**

Left �.160 .112 �.051 .527 �.014 .892 .185 .021 .419 <.001 .154 .055 .388 <.001 .087 .283 .256 .011 .209 .009

Right �.112 .267 �.058 .475 �.087 .391 .252 .002 .200 .050 .319 <.001 .234 .020 .300 <.001 .168 .097 .185 .021

Left BF .002 .981 .195 .105 �.043 .672 �.055 .498 .282 .005 .079 .328 .279 .005 .004 .957 .115 .258 .017 .832

Right BF .023 .823 .069 .394 �.087 .390 �.039 .631 .266 .008 .044 .583 .257 .010 .020 .810 .074 .465 �.051 .525

FPT (mm/s)*

FT �.035a .769 �.152 .058 .176a .134 .150 .062 .135c .255 .045 .581 �.104d .378 .021 .794 �.305d .008 �.016 .845

FT BF �.040a .736 �.107 .187 .421a <.001 .193 .016 .214c .069 .104 .198 �.004d .971 �.067 .406 �.195d .095 �.090 .263

SS �.132a .262 �.053 .516 .176a .134 .020 .807 �.085c .477 �.112 .164 �.186d .113 �.187 .020 �.196d .094 �.146 .070

SS BF �.079a .502 �.051 .529 .086a .464 .123 .129 �.168c .155 �.083 .308 �.217d .063 �.127 .116 �.252d .030 �.079 .332

Left �.095 .346 .118 .144 .099 .327 .214 .007 �.177 .082 .119 .140 �.187 .063 .006 .944 �.125 .217 �.025 .760

Right �.115 .253 �.115 .153 .035 .728 .251 .002 �.201 .048 .168 .037 .215 .033 .076 .351 �.108 .288 �.028 .733

Left BF �.120 .234 �.130 .108 .160 .113 .125 .120 .043 .678 .075 .353 �.169 .095 �.034 .677 �.157 .120 �.171 .033

Right BF �.149 .138 �.114 .157 .128 .203 .241 .003 �.148 .148 .038 .642 �.242 .016 �.087 .284 �.206 .041 �.114 .157

(a,b,c,d,e) Means the number of subjects that participated in that test. TUGT, timed up and go test; FRT, functional reach test; OLS, one-leg stance; FPT, force platform test; FT, feet together; SS, semi standing; BF,

blindfolded; CMJ, counter movement jump; BSTEET, Biering-Sørensen trunk extensor endurance test; ID, subject with intellectual disability; non-ID, subject without intellectual disability; r, value of correlation;

and p, value of significance.

* Pearson’s correlation coefficient.

** Spearman’s correlation coefficient. Significance level was set to a p-value of 0.002 and levels achieved are in bold type in the table.

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S. Blomqvist et al. / Research in Developmental Disabilities 34 (2013) 198–206 205

In contrast, Carmeli et al. (2008) reported less sway in a controlled study on a group of adults with ID. One reason for thiscould be that Carmeli et al. had a small group of only 15 participants with ID, which perhaps was insufficient to cover thevariation within a population. They also reported that the ratio between EO and BF sway area increased more for the controlgroup than the ID groups (Carmeli et al., 2008). Our results support however the findings by Carmelli et al. that participantswith ID do not have a more visually dominated postural balance than participants without ID. This also holds true foradolescents with ID.

A significant difference for ETUGT was found between groups in that the ID group performed significantly worse.However, as the difference was only 1 s, the clinical significance can certainly be questioned. Carmeli, Bar-Chad, Lotan,Merrick, and Coleman (2003) tested ETUGT on people with mild ID with a mean age of 60 years and found that theyperformed the test 6 s slower than people without ID (Carmeli et al., 2003). In contrast, this distinction could be clinicallyimportant. It appears that people with ID lose their postural balance ability more with ageing then people without ID(Lahtinen et al., 2007), which indicates the need to tackle the situation at an early age, possibly by physical training ofreduced bodily functions.

Our study shows no significant correlations between BMI and postural balance. Another study reports that obese andexcessively obese male adults without ID improved their postural balance after lowering their BMI (Handrigan et al., 2010),and one study suggests that BMI has an impact on the ability to maintain postural balance in prepubertal boys (Deforcheet al., 2009). In our study the BMI mean were between 22.4 and 25.0, which are within normal BMI weight classifications foryoung people under 18.

Low significant correlations were found between MFRT and height in both groups, which is also reported by Duncan et al.(1990). Regarding the other postural balance tests in this study, height seems not to play a large role in postural balanceability. Granacher and Gollhofer (2011) report no correlation between muscle performance and body sway for adolescents,as in this study. Our study found a low correlation between some of the postural balance and muscle performance tests, butmuscle performance seems not to have any great role in the postural balance ability of adolescents with and without ID,which is in opposite of what has been reported among elderly (Wiacek et al., 2009).

Although the results are presented for the group of men and women as a whole it could be seen that adolescent womenwith ID appear to have a lower sway velocity than men with ID, for reasons we do not know. Further studies are necessary toinvestigate these gender differences.

There are some limitations that should be addressed. First, this study includes only people with mild to moderate ID, sonothing is known about postural balance in adolescents with severe and profound ID. Hale, Bray, and Littmann (2007) foundthat many of the standardized tests are not suitable for this population because the testes are too difficult to comprehend.New understandable postural balance tests should be developed for this group (Hale et al., 2007). Second, inter-raterreliability is not known for the tests that were used in this study, but all test leaders was trained and educated which alsoincluded practical performance and discussions on consensus. Third, a ceiling effect in both groups was found for OLS andDOLS, when not BF. If these tests are to be used for this group in the future, they must be developed to make them morechallenging.

5. Conclusion

Adolescents with ID have poorer postural balance than age-matched controls. Adolescents with ID do not rely more onvision to keep their postural balance than to their peers without ID. Muscle performance and height play a minor role inpostural balance performance and BMI does not affect the postural balance for adolescents.

Conflict of interest

The authors declare that they have no conflict of interest related to the submitted manuscript

Acknowledgement

Dr. Leif Nilsson, Mathematics and Mathematical Statistics at Umea University, performed the power calculations.

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