Abstract
Background:
Older females have less dynamic postural control and muscle strength than do middle-aged females. Aging-related strength losses may limit balancing performance.
Objective:
The purpose of this study was to investigate the ability of the Y Balance Test (YBT) and lower limb strength to discriminate between females in 2 age groups, the relationship between YBT distance and the Berg Balance Scale (BBS), and the degree to which performance on YBT distance is related to lower limb strength in middle-aged and older females.
Method:
The 40 healthy, independently active females were divided into 2 groups: older and middle-aged. The participants underwent measurements of YBT distance using the YBT, maximal muscular strength of the lower limbs using a handheld dynamometer, and the BBS.
Results:
The YBT distance in 3 directions and lower limb muscle strength for both lower limbs were significantly lower in the older adults than in the middle-aged group. A moderate correlation but insignificant correlation was found between the YBT composite distance and the BBS score. In the older females, YBT distance was significantly positively correlated with strength of the knee flexor and hip abductor. In the middle-aged group, YBT distance was significantly positively correlated with strength of the knee flexor and hip extensor.
Conclusions:
Performance on the YBT was influenced by the strength of lower limb. We suggested that YBT can be used to alternative as a measurement of dynamic balance. Proper training programs for older people could include not only strengthening exercises but also YBT performance to improve balance.
aging; Berg Balance Scale; lower limb strength; physical therapy; Y Balance Test
Introduction
In older adults, high levels of lower limb strength and balance are important
prerequisites for the independent and successful performance of activities of daily
living. Age-related musculoskeletal changes lead not only to muscle strength and
mass decline but also limit balance and gait11 Kallman DA, Plato CC, Tobin JD. The role of muscle loss in the
age-related decline of grip strength: cross-sectional and longitudinal
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. These changes are closely related to the
incidence of falls. In older adults, falls can cause severe injuries such as hip
fractures (50%), arm fractures (13%), and head injuries (10%) or even death33 Sattin RW, Lambert Huber DA, DeVito CA, Rodriguez JG, Ros A,
Bacchelli S, et al. The incidence of fall injury events among the elderly in a
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, changes in posture66 Woodhull-McNeal AP. Changes in posture and balance with age. Aging
(Milano). 1992;4(3):219-25. PMid:1420405 ., and lower
postural stability77 Lord SR, Ward JA. Age-associated differences in sensori-motor
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. The decrease in strength
seems to be explained, to a great extent, by the reduction in muscle mass, perhaps
related to a decline in the intensity of daily physical activities88 Mälklä E, Impivaara O, Heliövaara J, Maatela J. The physical
activity of healthy and chronically ill adults in Finland at work, at leisure
and during commuting. Scand J Med Sci Sports. 1994;4(1):82-7.
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. Previous studies have reported dynamic
balance decreases with age99 Bouillon LE, Sklenka DK, Driver AC. Comparison of training between 2
cycle ergometers on dynamic balance for middle-aged women. J Sport Rehabil.
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,
1010 Bouillon LE, Baker JL. Dynamic balance differences as measured by
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. Bouillon and Baker1010 Bouillon LE, Baker JL. Dynamic balance differences as measured by
the Star Excursion Balance Test between adult-aged and middle-aged women. Sports
Health. 2011;3(5):466-9. http://dx.doi.org/10.1177/1941738111414127 .
PMid:23016044.
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reported that postural control scores based on the Star
Excursion Balance Test (SEBT) were lower in older females than in younger females.
However, there is a lack of age-related differences in various measures of lower
limb strength and dynamic balance between middle-aged and older females.
The Berg Balance Scale (BBS) has been widely used to assess dynamic and static
balance in older adults. The BBS includes 14 items that are common in everyday life.
In the clinical setting, the BBS is easy to apply and assesses balance in older
adults to help predict the risk of falling1111 Steffen TM, Hacker TA, Mollinger L. Age- and gender-related test
performance in community-dwelling elderly people: six-minute walk test, berg
balance scale, timed up & go test, and gait speeds. Phys Ther.
2002;82(2):128-37. PMid:11856064 ..
However, some studies have reported that the BBS is unreliable for screening the
risk of falls among older adults1212 Bogle Thorbahn LD, Newton RA. Use of the Berg Balance Test to
predict falls in elderly persons. Phys Ther. 1996;76(6):576-83. PMid:8650273
.
13 Shumway-Cook A, Baldwin M, Polissar NL, Gruber W. Predicting the
probability for falls in community-dwelling older adults. Phys Ther.
1997;77(8):812-9. PMid:9256869 .
-
1414 Muir SW, Berg K, Chesworth B, Speechley M. Use of the Berg Balance
Scale for predicting multiple falls in community-dwelling elderly people: a
prospective study. Phys Ther. 2008;88(4):449-59.
http://dx.doi.org/10.2522/ptj.20070251 . PMid:18218822.
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. Despite its high reliability and
validity1111 Steffen TM, Hacker TA, Mollinger L. Age- and gender-related test
performance in community-dwelling elderly people: six-minute walk test, berg
balance scale, timed up & go test, and gait speeds. Phys Ther.
2002;82(2):128-37. PMid:11856064 ., the BBS may not be the most
appropriate test of mobility or balance. Because this clinical observational tool is
scored on an ordinal scale, it may not be sufficiently sensitive to change,
particularly in active older adults with high levels of balancing ability. Given the
low sensitivity of the BBS for balance limits, and that it has a ceiling effect, a
new test should be developed to measure balance in a more challenging way for active
older women.
The Y Balance Test-YBT (Move2Perform, Evansville, IN, USA) is a dynamic balance test
that may be less likely than the BBS to demonstrate a ceiling effect. The YBT is
essentially an instrumented version of the components of the SEBT, and it was
developed to improve measurement repeatability and to standardize the performance of
the test1515 Plisky PJ, Gorman PP, Butler RJ, Kiesel KB, Underwood FB, Elkins B.
The reliability of an instrumented device for measuring components of the star
excursion balance test. N Am J Sports Phys Ther. 2009;4(2):92-9. PMid:21509114
.. The YBT incorporates reaching in
3 directions (anterior, posteromedial, and posterolateral) with the unsupported
lower limb while in a single-limb stance on a centralized stance platform. In sports
players, the YBT can be used for injury prediction and performance
discrimination1616 Butler RJ, Southers C, Gorman PP, Kiesel KB, Plisky PJ. Differences
in soccer players' dynamic balance across levels of competition. J Athl Train.
2012;47(6):616-20. http://dx.doi.org/10.4085/1062-6050-47.5.14 .
PMid:23182008.
http://dx.doi.org/10.4085/1062-6050-47.5...
. The benefits of the YBT
are that it has a standard protocol and high inter-rater (0.991.00) and intra-rater
(0.850.91) reliabilities1313 Shumway-Cook A, Baldwin M, Polissar NL, Gruber W. Predicting the
probability for falls in community-dwelling older adults. Phys Ther.
1997;77(8):812-9. PMid:9256869 .. However, there
was no previous study demonstrating the reliability of the YBT in middle-aged and
older females. Nevertheless, the YBT can be used to test and train simultaneously,
which is beneficial for the development of rehabilitation and training programs.
From a therapist's point of view, knowledge of the relationship between the strength of the lower limb muscles and balance may be important for both the identification of older adults with an increased risk of falling and the development of fall-preventive training programs. Despite evidence demonstrating the importance of prevention of falling in older females, the relationship between the strength of the lower limbs and balance is not fully understood. By understanding the relationship between the YBT and strength, we can obtain more clinical information regarding which exercises would best help middle-aged and older females to achieve a long YBT distance. We believe that repeated investigation of the training to extend the YBT distance during one-leg standing will provide beneficial information to clinicians for prevention of falls in older females. Thus, the first purpose of this study was to compare lower limb strength and the YBT distance in 3 directions in middle-aged and older females. The second purpose was to assess any relationship between the YBT distance and the BBS in older females and to determine any relationship between the YBT distance and lower limb strength in middle-aged and older females.
Method
Study design
This cross-sectional study required each participant to be assessed for YBT distance (anterior, posteromedial, and posterolateral), maximal muscular strength of the lower limbs (hip extension, hip flexion, hip abduction, knee extension, knee flexion, and ankle dorsiflexion), and BBS score. The study sample was divided into 2 groups at 65 years: middle-aged and older women. This was a correlational study of relationships among YBT distance, the BBS, and lower limb strength in middle-aged and older females. All subjects read and signed an informed consent form approved by the Inje University Ethics Committee, Gimhae, Gyeongsangnam-Do, South Korea (approval number 2014067) for Human Investigations prior to participation.
Subjects
The 40 female participants, aged 45-80 years, volunteered for this study and were categorized into age groups: middle-aged (45-60 years) or older (70-80 years). There were 20 middle-aged females (53.9±5.0 years; 56.0±6.2 kg; 159.8±4.7 cm) and 20 older females (77.5±2.7 years; 51.7±7.7 kg; 152.8±4.4 cm). The older females were recruited from senior citizen centers in Haeundae, Busan, Republic of Korea. The middle-aged females were recruited from the community. Participants were healthy, living independently, were self-ambulatory without a cane or walker, and had no history of falls. Participants with self-reported neurological disease, musculoskeletal problems, visual impairment, or vestibular disease were excluded. Older females with comprehension deficits or disabilities that might limit the tasks of performance on the YBT or the BBS were also excluded.
Y Balance Test
The YBT is a reliable and valid tool for quantitative balance assessment1313 Shumway-Cook A, Baldwin M, Polissar NL, Gruber W. Predicting the
probability for falls in community-dwelling older adults. Phys Ther.
1997;77(8):812-9. PMid:9256869 .. The participants reached with one foot
in the anterior, posteromedial, and posterolateral directions during standing on
the other foot on a central plastic footplate. All testing and practices were
performed barefoot with both the left and right limbs to eliminate additional
balance and stability from the shoes1717 Gribble PA, Hertel J. Effect of lower-extremity muscle fatigue on
postural control. Arch Phys Med Rehabil. 2004;85(4):589-92.
http://dx.doi.org/10.1016/j.apmr.2003.06.031 . PMid:15083434.
http://dx.doi.org/10.1016/j.apmr.2003.06...
.
Each subject was allowed 6 practice trials in each direction and on each leg
prior to formal testing for familiarization, then conducted 3 test trials in
each direction and the mean value of the 3 test trials was determined for data
analysis. We allowed rest on a chair for 3 min between practice and recorded
trials, but not between trials. The subject maintained a single-leg stance with
hands on the pelvis while pushing a rectangular reach-indicator block with the
contralateral leg as far as possible along the 3 directions (Figure 1). The reach distance was recorded
to the nearest 0.5 cm as the point at which the reach-indicator block was pushed
closest to the central footplate. The specific testing order was right anterior,
left anterior, right posteromedial, left posteromedial, right posterolateral,
and left posterolateral (a consistent testing protocol was established to
improve the reproducibility of the test).
A trial was classified as invalid if the participant did not return to the starting position, kicked the plate with the reaching foot to gain more distance, failed to maintain a unilateral stance on the platform, stepped on top of the reach indicator for support, or removed her hands from her hips. If an invalid trial occurred, the data were discarded, and the subject repeated the trial.
For normalization, the participants' lower limb length while lying in the supine
position (anterosuperior iliac spine to the center of the ipsilateral medial
malleolus) was measured in centimeters bilaterally. For data analysis, the reach
distance in each direction was normalized to the lower-limb length by
calculating the maximized reach distance (%MAXD) using the formula (6 excursion
distance/ both lower-limb length × 3) × 100 = % MAXD because of leg length
differences within individuals1818 Robinson RH, Gribble PA. Support for a reduction in the number of
trials needed for the star excursion balance test. Arch Phys Med Rehabil.
2008;89(2):364-70. http://dx.doi.org/10.1016/j.apmr.2007.08.139 .
PMid:18226664.
http://dx.doi.org/10.1016/j.apmr.2007.08...
. The sum
of 6 normalized reach distances (right and left in all 3 directions) was then
averaged to generate a composite distance.
Handheld Dynamometer
A digital handheld dynamometer (HHD; PowerTrack II, JTech Medical, Salt Lake
City, UT) was used to measure the maximum voluntary strength in each
participant. As in the BBS, the rater was a physical therapist with 5 years of
experience. The maximal isometric strength of the bilateral hip extensors,
flexors, and abductors, knee extensors and flexors, and ankle dorsiflexors was
assessed by physical therapists with 5 years of experience using the PowerTrack
II on each limb separately. We did not measure the isometric force of the ankle
plantar flexors because handheld dynamometry provides unreliable measures of
ankle plantar flexor strength1919 Arnold CM, Warkentin KD, Chilibeck PD, Magnus CR. The reliability
and validity of handheld dynamometry for the measurement of lower-extremity
muscle strength in older adults. J Strength Cond Res. 2010;24(3):815-24.
http://dx.doi.org/10.1519/JSC.0b013e3181aa36b8 . PMid:19661831.
http://dx.doi.org/10.1519/JSC.0b013e3181...
. The
testing positions, based on Wang et al.2020 Wang CY, Olson SL, Protas EJ. Test-retest strength reliability:
hand-held dynamometry in community-dwelling elderly fallers. Arch Phys Med
Rehabil. 2002;83(6):811-5. http://dx.doi.org/10.1053/apmr.2002.32743 .
PMid:12048660.
http://dx.doi.org/10.1053/apmr.2002.3274...
, are described in Table 1.
Participants were told to stop contracting when the tester finished counting to
5 seconds because this duration was shown to be adequate for most subjects to
reach the maximum force in a previous study2121 Bohannon RW. Testing isometric limb muscle strength with
dynamometers. Crit Rev Phys Med Rehabil. 1990;2:75-86.. The mean peak value of these 3 measurements was used for the
data analysis.
Berg Balance Scale
To gain an understanding of the participants' static and dynamic balance abilities, assessments were carried out with the BBS, a 14-item summative ordinal scale evaluating postural changes from sitting to standing and vice versa, transfers, sitting balance, and a variety of other standing balance tasks2222 Berg KO, Wood-Dauphinee SL, Williams JI, Maki B. Measuring balance in the elderly: validation of an instrument. Can J Public Health. 1992;83(Suppl 2):S7-11. PMid:1468055 .. The rater was a physical therapist with 5 years of experience. Among the 14 items, tandem standing and single-leg standing have been described as the most difficult2222 Berg KO, Wood-Dauphinee SL, Williams JI, Maki B. Measuring balance in the elderly: validation of an instrument. Can J Public Health. 1992;83(Suppl 2):S7-11. PMid:1468055 .; in our study, some older females obtained low scores for these items. The BBS has demonstrated excellent inter-rater reliability (intraclass correlation coefficient = 0.99) and test-retest reliability (intraclass correlation coefficient = 0.98)2222 Berg KO, Wood-Dauphinee SL, Williams JI, Maki B. Measuring balance in the elderly: validation of an instrument. Can J Public Health. 1992;83(Suppl 2):S7-11. PMid:1468055 .. However, the BBS may not be the most appropriate test of mobility or balance because of the ceiling effect in active community-living older females.
Statistical analysis
Data were analyzed using the SPSS software (ver. 18.0; SPSS, Chicago, IL, USA). After testing for a normal distribution using the Kolmogorov-Smirnov test, significant differences between the groups (middle-aged and older females) were identified using the independent ttest for YBT distance and muscle strength. The significance level was set at p<0.05 and was adjusted for multiple hypothesis tests (padj<0.008 (0.05/6) and padj<0.007 (0.05/7)). In each group, Pearson's correlation coefficients were used to quantify the linear relationships among YBT composite distance, the BBS score, and muscle strength. The correlation significance level was set at p<0.01 for a strong presumption against the null hypothesis. Intraclass correlation coefficients (ICC) were used to quantify test-retest reliability of the YBT. The ICC model (3,1) was used.
Results
Tables 2 and 3 summarize the mean ± SD of YBT distance and strength. Same-day intra-rater reliability was also calculated from 3 repeat tests done on day 1 by rater 1 and all measurements were highly reliable (ICC=0.92 to 0.97; Table 2). The 3 reach directions for both lower limbs in the YBT and lower limb muscle strength tests were significantly higher and longer in middle-aged females than in older females (padj<0.008 or padj<0.007; Tables 2, 3). The mean BBS score ± SD of the older females was 55.1±1.1 (range: 52-56); the middle-aged females exhibited a perfect BBS score.
In the older group, there was a fair relationship but insignificant correlation was found between the YBT composite distance and the BBS score. Right hip abductor, right knee flexor, and left knee flexor strength were positively correlated with the YBT composite distance.
In the middle-aged group, right hip extensor, left hip extensor, and right knee flexor strength were positively correlated with the YBT composite distance.
Discussion
Several previous studies reported that older adults have significantly lower limb strength and balance ability than do middle-aged females2323 Weirich G, Bemben DA, Bemben MG. Predictors of balance in young, middle-aged, and late middle-aged women. J Geriatr Phys Ther. 2010;33(3):110-7. PMid:21155505 .. The results of the present study indicated that the YBT distance and the lower limb strength in each muscle were significantly lower in older adults than in middle-aged females. However, muscle group strength in the different age groups was inconsistently correlated with the YBT composite distance.
The findings of this study also indicated that the lower limb muscle strength of the
older adult group was significantly lower than that of the middle-aged group. Aging
causes quantitative and qualitative alterations in the neuromuscular system,
especially a generalized loss of skeletal muscle mass and strength. In males, lower
limb strength declines gradually2424 Doherty TJ. Invited review: Aging and sarcopenia. J Appl Physiol
(1985). 2003;95(4):1717-27. http://dx.doi.org/10.1152/japplphysiol.00347.2003 .
PMid:12970377.
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, whereas
in females it declines sharply after menopause2525 Hughes VA, Frontera WR, Roubenoff R, Evans WJ, Singh MA.
Longitudinal changes in body composition in older men and women: role of body
weight change and physical activity. Am J Clin Nutr. 2002;76(2):473-81.
PMid:12145025 .. Many factors associated with inactivity contribute to this decline
in lower limb strength, such as a low score on the activities of daily living scale,
balance abnormalities2626 Baumgartner RN, Koehler KM, Gallagher D, Romero L, Heymsfield SB,
Ross RR, et al. Epidemiology of sarcopenia among the elderly in New Mexico. Am J
Epidemiol. 1998;147(8):755-63.
http://dx.doi.org/10.1093/oxfordjournals.aje.a009520 .
PMid:9554417.
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, bed rest, or a
sedentary lifestyle2727 Cruz-Jentoft AJ, Baeyens JP, Bauer JM, Boirie Y, Cederholm T, Landi
F, et al. Sarcopenia: European consensus on definition and diagnosis: Report of
the European Working Group on Sarcopenia in Older People. Age Ageing.
2010;39(4):412-23. http://dx.doi.org/10.1093/ageing/afq034 .
PMid:20392703.
http://dx.doi.org/10.1093/ageing/afq034...
. A reduction in lower
limb strength could have deleterious effects on the performance of basic activities
of daily living and contribute to an increased risk of falls2828 Lawrence RH, Jette AM. Disentangling the disablement process. J
Gerontol B Psychol Sci Soc Sci. 1996;51(4):S173-82.
http://dx.doi.org/10.1093/geronb/51B.4.S173 . PMid:8673646.
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,
2929 Barry BK, Carson RG. The consequences of resistance training for
movement control in older adults. J Gerontol A Biol Sci Med Sci.
2004;59(7):730-54. http://dx.doi.org/10.1093/gerona/59.7.M730 .
PMid:15304540.
http://dx.doi.org/10.1093/gerona/59.7.M7...
. Consistent with previous studies, there
was a significant difference between the middle-aged and older adult groups.
However, Sousa et al.3030 Sousa N, Mendes R, Abrantes C, Sampaio J, Oliveira J. Is once-weekly
resistance training enough to prevent sarcopenia?. J Am Geriatr Soc.
2013;61(8):1423-4. http://dx.doi.org/10.1111/jgs.12387 .
PMid:23937497.
http://dx.doi.org/10.1111/jgs.12387...
reported that
once-weekly sessions of resistance training are sufficient to improve muscle
strength. It is important that therapists and other healthcare practitioners
recommend appropriate exercises or training programs for the recovery of strength in
the elderly.
An exploratory finding was that, across all participants, all directions of the YBT
were significantly lower in the older adult group than in the middle-aged group.
Bouillon and Baker1010 Bouillon LE, Baker JL. Dynamic balance differences as measured by
the Star Excursion Balance Test between adult-aged and middle-aged women. Sports
Health. 2011;3(5):466-9. http://dx.doi.org/10.1177/1941738111414127 .
PMid:23016044.
http://dx.doi.org/10.1177/19417381114141...
reported that younger
females were able to reach approximately 7 cm farther than middle-aged females
during the anterior, anteromedial, and posteromedial directions in the SEBT.
Differences between groups may be assumed to be the result of decreased lower
extremity strength or range of motion. Thus, we measured lower limb strength and
confirmed that the strength of all muscle groups in both lower limbs was less in
older than in middle-aged females; this may affect dynamic postural control. Thus,
it may be that dynamic postural control can be improved by increasing lower limb
strength in older females; however, further study is needed to evaluate targeted
strength interventions. Moreover, the decreased distance in older females during YBT
performance suggests that older adults have more difficulty than middle-aged adults
in maintaining a posture with a single-limb stance on a limited support base
(central plastic footplate). The single-limb stance is a significant challenge for
older adults so caution is needed to prevent falling during YBT performance.
Brauer et al.3131 Brauer SG, Burns YR, Galley P. A prospective study of laboratory and
clinical measures of postural stability to predict community-dwelling fallers. J
Gerontol A Biol Sci Med Sci. 2000;55(8):M469-76.
http://dx.doi.org/10.1093/gerona/55.8.M469 . PMid:10952371.
http://dx.doi.org/10.1093/gerona/55.8.M4...
assessed the balance of 100
healthy older females with a mean age of 73.0±5.0 years and reported that the BBS
results indicated a ceiling effect for the groups both with and without a history of
falls. In addition, Newton3232 Newton RA. Balance screening of an inner city older adult
population. Arch Phys Med Rehabil. 1997;78(6):587-91.
http://dx.doi.org/10.1016/S0003-9993(97)90423-8 . PMid:9196465.
http://dx.doi.org/10.1016/S0003-9993(97)...
suggested that
modifications should be made to the BBS when it is applied to active older adults.
This means that the BBS cannot predict a risk of falling at high levels of balance
ability. Participants in this study gained a BBS score close to the maximum (>52
points), and the BBS is not sufficiently sensitive in active older adults.
Therefore, the BBS cannot be recommended for this population because of the ceiling
effect. The tasks of the BBS in healthy elderly people may not be sufficiently
challenging to detect subtle balance deficits, so there is a need for alternative
measures, such as the YBT. The BBS is scored on an ordinal scale; however, the YBT
distance is measured on a ratio scale. In addition, an advantage of the YBT is its
ability to simultaneously perform both functional performance testing and
training.
In our study, a significantly strong relationship was noted between the YBT composite
distance and the knee flexor strength in both the older and middle-aged groups. The
SEBT showed that the greatest amount of knee flexion ROM occurred during performance
of the anteromedial reach3333 Earl JE, Hertel J. Lower-extremity muscle activation during the Star
Excursion Balance Tests. J Sport Rehabil. 2001;10:93-104.. To perform the
YBT, subjects lean forward and backward to maintain their balance, and gravity
acting on the upper body creates a large knee-flexion moment. Consequently, the knee
flexor may contribute to a greater YBT distance when the body sway is converted from
forward to backward. This finding is supported by previous research that indicated
increased hamstring activity when a leg is extended backwards; the trunk flexes to
maintain balance3232 Newton RA. Balance screening of an inner city older adult
population. Arch Phys Med Rehabil. 1997;78(6):587-91.
http://dx.doi.org/10.1016/S0003-9993(97)90423-8 . PMid:9196465.
http://dx.doi.org/10.1016/S0003-9993(97)...
. The YBT reaching included
2 of the 3 directions (i.e. posteromedial and posterolateral) when the leg is
extended backwards. Hubbard et al.3434 Hubbard TJ, Kramer LC, Denegar CR, Hertel J. Correlations among
multiple measures of functional and mechanical instability in subjects with
chronic ankle instability. J Athl Train. 2007;42(3):361-6. PMid:18059991
. reported
that posteriomedial and posteriolateral excursion during the SEBT are correlated
with hip abduction and extension strength. However, we found a correlation between
the YBT composite distance and the lower limb strength. The findings of this study
showed that the hip abductor was positively correlated with the YBT composite
distance in the older adult group, but that the hip extensor was correlated with the
YBT composite distance in the middle-aged group. An increased hip flexion range of
motion is required for a greater reaching distance in SEBT, which may have led to an
increased demand on hip extensor strength to maintain postural control3535 Robinson R, Gribble P. Kinematic predictors of performance on the
Star Excursion Balance Test. J Sport Rehabil. 2008;17(4):347-57. PMid:19160909
.. Based on our results, it may be inferred
that low hip extensor strength (32.7 kg) could be substituted by strong hip abductor
strength (53.6 kg), as the hip abductor can contribute to the YBT distance in the
older group. These findings suggest that differences between groups may play a role
separate from balance strategy according to the changes in muscle strength with
aging. Therefore, clinicians should consider different treatments according to age
by assessing performance in the YBT. There were significant correlations between the
YBT test and strength measures for both age groups but, in fact, the relationships
were only significant in 25% of the muscle groups tested in the older group (3/12)
and younger groups (3/12). A post hoc power analysis determined that at least 19
subjects were necessary to establish statistical significance at a power of .90,
which supports the significance of our findings.
Our study had some limitations. When interpreting the results, the constraints of our cross-sectional research design must be considered. We recruited a group of females with no history of falls. The BBS as a comparison measure of balance was inappropriate because of a ceiling effect. However, we used BBS as a dynamic balance measurement to assess the test in active older females. We did not measure the range of motion in the lower extremities because the available lower extremity range of motion for ankle dorsiflexion and the hip internal and external range of motion that participants exhibited did not influence the reaching distance3636 Nakagawa L, Hoffman M. Performance in static, dynamic, and clinical tests of postural-control in individuals with recurrent ankle sprains. J Sport Rehabil. 2004;13:255-68.. We did not consider a small potential effect of fatigue during the YBT. We supervised the movements of body sway for fear of falling by visual judgment during YBT performance. Although visual judgment is used widely in the clinical setting, further study would be useful to provide objective validity using a motion analysis system. Additionally, future studies should assess relationships between each direction distance in YBT and lower limb strength. Although the YBT is not available for balance assessment in all clinical facilities, the present findings provide a fundamental framework from which to expand and develop the YBT.
Conclusions
The present findings provide clinicians with useful information regarding the relative contribution of muscle strength to YBT performance when evaluating dynamic balance, but differences were observed between the middle-aged and older adult groups. In older females, the decreased ability for dynamic balance by YBT distance could be associated with declined muscle strength. We recommend that therapists and other healthcare practitioners use YBT performance in the development of rehabilitation and training programs in older people; however, further studies are needed to determine the clinical utility of this test.
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Publication Dates
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Publication in this collection
29 May 2015 -
Date of issue
May-Jun 2015
History
-
Received
18 July 2014 -
Accepted
21 Nov 2014