INTRODUCTION AND PURPOSE
The development of postural control in children typically occurs in a stage-like progression, based on development of specific systems involved in postural control.1,2 Standing balance is regulated by a complex mix of systems, including the visual, vestibular, somatosensory, and musculoskeletal systems.3–5 Development of each system varies with age. The somatosensory system matures first and the vestibular system last.6 Postural control therefore develops as each system reaches the necessary threshold to support the associated behavior.5,7
Postural control is defined here as the ability to keep the center of mass over the base of support.8 Dynamic balance (DB) is operationally defined as the ability to maintain postural control during movements, such as reaching or walking.9 Dynamic balance is an essential physical therapy examination component for children. Measures of DB can be used before and after physical therapy interventions to determine the effect of specific treatment strategies on desired outcomes. Pediatric therapists need to understand DB measures and the relationship between age and DB. Various measures are available to assess DB including the Timed Up and Go (TUG) test,10 Pediatric Reach Test (PRT),11 and Pediatric Balance Scale (PBS).12 Unfortunately, the evidence for using many DB measures in the pediatric population is limited.
Although measures of DB are important elements of examination, which measures correlate with specific ages or how anthropometric variables might influence balance is unclear. Important precursors for appropriate use of balance measures in the pediatric population include understanding the influence of anthropometrics during balance measurement as well as the interrelationships among age, gender, and DB. The purpose of this study was to examine relationships among age, gender, and DB in children aged 5 to 12 years during performance on the TUG test, PBS, and PRT. A secondary purpose was to examine the influence of various anthropometric variables, including height, weight, arm length, and foot length, on balance abilities.
Postural control and balance abilities vary across age levels due to the maturation of the systems that contribute to postural control, including the visual, somatosensory, and vestibular systems.1,2 Shumway-Cook and Woollacott1 reported a transition from immature to mature balance responses between the ages of 4 and 10 years. Children in the 4- to 6-year age group begin to use somatosensory information appropriately and develop balance strategies for control with altered balance conditions.1,13–16 Seven- to 10-year-old children use more mature strategies with altered conditions,1 developing better visual control and integrating vision with other sensory information.13 Largo et al17 found that motor performance, including balance abilities, was dependent on developmental status and age between 5 and 18 years, with balance leveling off in early adolescence. While some authors indicated that children as young as 9 years exhibited adult postural strategies,1 others have suggested that adult postural strategies are used near early adolescence.6
Many authors have discussed variations in postural control related to age and gender. Nolan et al4 found age and gender differences in standing balance in children aged 9 to 16 years. Odenrick and Sandstedt18 and Riach and Hayes19 found that movements of the center of pressure stabilized earlier in girls than in boys. Sellars20 found a significant gender difference on the 1-foot standing balance test in children with a mean age of 61 months with girls demonstrating higher quality static balance than boys. Donahoe et al21 reported that age, not gender, contributed to variance in balance measured by the Functional Reach Test (FRT). Habib et al22 examined balance abilities in children aged 5 to 13 years and found both age-related and gender differences. All children demonstrated improved balance abilities with increasing age, and variation occurred between genders depending on socioeconomic status (SES). In the high SES group, boys demonstrated superior balance compared to girls; however, in the lower SES group, girls exceled in static balance activities.22 In contrast, Williams et al23 found no significant difference in mean TUG scores between males and females aged 3 to 9 years.
Various anthropometric variables may influence postural control or balance abilities. Habib and Westcott24 found base of support (length of foot) predicted FRT scores when examining all ages combined. They also reported height as a predictor of scores on the TUG test in all children and on the PRT in the younger children only. In a recent study by Norris et al,25 weight was the only anthropometric variable found to predict FRT scores in children aged 3 and 4 years. Although Donahoe et al21 did not find height, weight, or arm length predicted FRT scores, Duncan et al26 reported an association with arm length and functional reach distance, and found functional reach could be predicted using height. From these equivocal findings, the influence that anthropometric variables may have on balance abilities measured by the TUG test, PBS, and PRT in 5- to 12-year-old children remains unclear.
Postural control is also dependent on task difficulty. Figura et al27 found task-dependent changes in standing balance in children 6 to 10 years of age. Centers of pressure were larger with more difficult tasks, specifically standing on one foot versus both feet close together. Streepey and Angulo-Kinzler28 reported that balance control was dependent on both age and reaching task difficulty. Significant differences were found between younger and older children with moderately difficult tasks. Because only reaching tasks were examined, the relationship between age and task difficulty with other DB activities is unclear.
Balance or postural control is influenced by multiple variables, including task constraints, biological competence and age, and environmental affordances.29–31 Habib et al24 suggested some important considerations when examining postural control and balance abilities: (1) postural stability is task-specific; (2) different balance tests evaluate various age- and gender-related aspects of balance; (3) postural control improves with increasing age and then plateaus in adolescence; and (4) age and gender interactions need to be considered in different balance tests. For these reasons, postural control should be examined across ages and gender in children, using a variety of balance tasks.
The study was exploratory, using a correlational design to examine DB in children using 3 balance scales: the PRT, PBS, and TUG test. The correlational design allowed the search for relationships between age, gender, and children's balance abilities.32 Each participant performed the same 3 DB measures in random order.
A convenience sample of children with typical development, aged 5 to 12 years, was recruited. A minimum of 5 years of age was established for participant selection because 5 years is considered a transition period in the development of postural control,1 and children younger than 5 years have greater difficulty following directions for the balance tests. For a medium effect size between 0.30 and 0.40, a sample of 100 children was needed to provide a power of 0.86 to 0.99.32 A selected study size of 160 met the medium effect size. The 160 participants included 20 subjects at each age from 5 to 12 years, with equal numbers of boys and girls in each group. Selection criteria for study participants were (1) age 5 to 12 years, (2) absence of neurological or orthopedic diagnoses, (3) no history of developmental delay or balance impairments, and (4) no orthopedic surgeries within the past 6 months. All diagnostic conditions and surgical histories were identified through parent report. The Rocky Mountain University of Health Professions Institutional Review Board approved the study. Parental permission and subject assent were obtained for all subjects.
The study took place in multiple settings: (1) elementary and middle schools in Newtown, Connecticut; (2) private schools in New Milford, West Haven, and Danbury, Connecticut; and (3) an outpatient rehabilitation facility in Stratford, Connecticut. Each school had a multiple-purpose room available for data collection, and a conference room was used in the outpatient rehabilitation facility.
Tests and Measures
Timed Up and Go
The time (seconds) for participants to stand up, walk 3 m, turn around, walk back, and sit in a chair is measured using the TUG test. The TUG test is a reliable and valid test of balance and functional mobility,22,23 demonstrating high interrater reliability with intraclass correlation coefficient (ICC) values of 0.8122 to 0.8923 and high test-retest reliability with an ICC of 0.83.23 The TUG test has also shown moderate to high validity with the Berg Balance Scale (BBS) (r = −0.72) and gait speed (r = −0.55).10
Pediatric Balance Scale
The PBS is a modified version of the BBS and includes 14 balance items, each scored from 0 to 4, with a total possible score of 56.12 In children the PBS is a reliable test of balance with high interrater (ICC = 0.99) and test-retest (ICC = 0.99) reliability.12 The validity of the PBS has not been reported.
Pediatric Reach Test
The PRT is a valid, reliable measure of postural control modified from the FRT, with the addition of reaching to the side and reaching in both sitting and standing.11 The PRT included 6 reaching activities with reach distance measured in centimeters or inches, with a sum of all distances as the final score.11 Moderate to high interrater reliability (ICC = 0.50-0.93) and test-retest reliability (ICC = 0.54-0.88) were demonstrated with the PRT. High construct validity has been found between the PRT and the measure of steadiness during standing (r = −0.79)11 and in children with cerebral palsy (CP), Gross Motor Function Classification System levels I-IV (rs = −0.88).11
A board-certified pediatric physical therapist (PCS) conducted training for research assistants (a physical therapist student and a pre–physical therapist student). Each research assistant, to ensure full understanding of the procedures for completing the balance measures, documenting data, and using the video camera, completed trials of the 3 balance measures. Training was completed after each assistant met appropriate levels of reliability with the PCS.
The PCS assessed intrarater reliability of the 3 tests with the first 10 participants to ensure acceptable reliability (ICC ≥ 0.75) before testing the 160 participants in the main study. Each research assistant also completed the intrareliability testing (5 participants per assistant). Pilot study intrarater reliability was 0.96 for the TUG test (P < .001), 1.0 for the PBS, and 0.81 for the PRT (P = .001). The pilot study was videotaped to examine procedural and reliability testing.
Participants removed their shoes before height, weight, and foot length were measured by the principal investigator. Each child was weighed in kilograms by using a portable digital scale and then moved to stand against the wall face out with both feet on a pad of paper. Height was marked on the wall, and foot length was marked on the paper on the floor. Height was measured in centimeters using a measuring tape from the floor to a mark placed on the wall. Foot length was measured in centimeters by using a measuring tape as the perpendicular distance from the back of the heel to the end of the big toe. Participant arm length was measured in centimeters from the base of the dominant middle finger to the acromion. All participants then donned shoes for a practice trial of the 3 balance assessments before testing began.
Test administration and verbal directions were adapted for children. Modifications to the TUG test were similar to the protocol used by Williams et al23: (1) children were given a concrete task of touching a star on the wall; (2) a seat without arms was used; (3) no qualitative instructions were used (eg, “walk as fast as you can”); and (4) timing began when the child left the seat instead of at the word “go.” The protocol for the PBS followed instructions developed by Franjoine et al12 for use with the modified version of the BBS. The procedures for the PRT followed the detailed instructions described by Bartlett and Birmingham.11
The TUG test, PBS, and PRT were performed in a computer-generated random order. Each subject's performance was videotaped to check scoring reliability. Two assistants rescored 5 different participants from the videotapes. The videotapes were randomly selected between the 80th and 100th participants. The primary investigator also scored the same participants from the videotapes to examine reliability and minimize examiner drift. Because examiner drift was not found (intrarater reliability: r = 0.98-1.0; interrater reliability: r = 0.86-1.0), additional training was not conducted.
To maintain consistency in measurement, the examiner read all directions and started and stopped each assessment. To minimize bias, the examiner reviewed the data only after all testing sessions were complete, except for the midstudy reliability data.
The average of 2 test trials was used to calculate the final score in seconds for the TUG test. One test trial per item occurred for the PRT with the total score for the PRT equaling the sum of all 6 items in centimeters. The PBS final score was the combined score of the 14 items, each worth between 0 and 4 points.
For the pilot study and midpoint reliability check, the ICC was used. The ICC (3,1) was used to determine the intrarater reliability for the PBS and PRT, and the ICC (3,2) was used to analyze the intrarater reliability for the TUG test.32 An ICC was also used to assess the interrater reliability during the midpoint check. The ICC (2,1) was implemented to explore the interrater reliability for the PBS and the PRT, and the ICC (2,2) was used to examine the interrater reliability for the TUG test.32
Means and standard deviations were calculated for the dependent variable TUG test, PRT and PBS scores and age, gender, height, weight, arm length, and foot length, the independent variables. The Pearson product moment correlation was used to analyze the relationships between age and the TUG test and between age and the PRT. The Spearman rank correlation coefficient was used to examine the relationship between age and the PBS. Point biserial correlations were implemented to investigate the correlations between gender and the TUG test, and gender and the PRT. Rank biserial correlation was used to assess the correlation between gender and the PBS. Finally, multiple linear regression was used to examine the associations between height, weight, arm and foot lengths, and the TUG test, PRT and PBS scores.
For this study, correlations from 0.00 to 0.25 indicated little to no relationship, 0.26 to 0.50 indicated fair relationship, 0.51 to 0.75 indicated moderate to good relationship, and greater than 0.75 indicated good to excellent relationship.32 An α level of 0.05 or less determined a statistically significant relationship. Interpretation of the significance of the correlation included the value of the correlation and the statistical significance. SPSS 13.0 (SPSS Inc, Chicago, Illinois) and Microsoft Excel 2007 (Microsoft Office) software were used for all data analyses.
Results of reliability testing completed mid-way through the study are included in Table 1. Intrarater and interrater reliability were high for the TUG test, the PRT, and the PBS.
Means and standard deviations for each balance measure by age are shown in Table 2. The mean TUG test values decreased with increasing age. The mean PBS scores increased with increasing age for years 5 to 7 and then plateaued for years 8 to 12 at the maximum possible score of 56. The mean PRT scores also increased with increasing age, except for years 9 and 10.
A significant negative correlation was found between age and balance scores on the TUG test (Table 3). Children aged 5 years took longer to complete the TUG test, whereas children aged 12 years took less time.
A significant positive correlation was found between age and balance scores on the PRT (see Table 3). Children aged 5 years reached a shorter distance than children aged 12 years.
Significant positive correlations were found between age and balance scores on the PBS for all children and for children aged 5 to 7 years (Table 3). Children aged 8 to 10 years and 11 to 12 years all scored the same value on the PBS, a maximum score of 56, leading to correlation values of 1.0.
Although a negative correlation between gender and DB was observed using the TUG test, no significant difference in scores was found between girls and boys (Table 4). A negative, nonsignificant correlation between gender and DB measured by the PRT was observed, indicating no significant difference in scores between girls and boys (Table 4). A positive but extremely low correlation between gender and DB was observed when using the PBS. No statistic has been recommended to determine significance32 (Table 4).
Means and standard deviations for each anthropometric variable by age category are presented in Table 5. For ages 5 to 12 years, the mean height increased with each year of age. The average weight increased consecutively with each year except for the 12-year-old group. The standard deviation for the 11-year-old group mean was high compared with the other standard deviations. Arm length also increased consecutively with each year except for the 12-year-old group. The mean foot length increased with each year of age.
Multiple linear regression analyses (Table 6) indicated that arm length was the strongest predictor of balance abilities on the PRT. Age was identified as the strongest predictor of balance abilities on the TUG test. Age was also determined to be the strongest predictor of balance abilities on the PBS. Table 7 reports the F values. Percentage of variance explained by the independent variables was found to be the strongest predictor of balance ability on the PBS, TUG test and PRT.
The results of this study indicated that the relationships between DB, age, and anthropometric characteristics (height, weight, arm length, and foot length) measured on the TUG test, PBS, and PRT varied with each balance measure.
In our sample, balance scores improved with increasing age from 5 to 12 years, supporting findings reported by Habib et al22 and Largo et al.17 Habib et al22 found decreasing values on the TUG test with increasing age. The mean TUG test values in this study were lower than those reported by Habib et al,22 particularly with the 12-year-old group; however, the trend in decreasing values was similar. The mean TUG test score in our sample of 160 children aged 5 to 12 years was 4.5 seconds. These TUG test scores are similar to those reported in studies of children in other countries. Habib et al22 found a mean TUG test score of 5.1 seconds for children from Pakistan, aged 5 to 13 years, and Williams et al23 reported a mean TUG test score of 5.9 seconds for children from Australia, aged 3 to 9 years. The testing protocol for this study followed the Williams et al23 guidelines, whereas Habib et al22 followed the original protocol established by Podsiadlo and Richardson.10 Although differences are present between the mean TUG test scores, it does not appear that they are due to the protocol because the mean from Habib et al22 falls between that found in this study and that reported by Williams et al.23
We found reach scores increased with age, consistent with reports in prior studies. Habib et al22 found increasing values on the FRT with increasing age in children aged 5 to 13 years. Norris et al25 also identified increasing values on the FRT with increasing age in children aged 3 to 5 years. It is difficult to compare additional details regarding reach values as previous studies have used the FRT, whereas we used the PRT in this study. Although the PRT has been specifically designed for use with children, scare evidence is available for comparative purposes.
In this sample, although PBS scores increased with age, they plateaued by 8 years. This finding is consistent with that of Franjoine et al,33 who found scores plateaued at 7 years. One explanation for this plateau in PBS scores is that the PBS uses an ordinal scale, and children with typical development can achieve the maximum criteria on the test items by 8 years. Kembhavi et al34 studied the BBS in children with CP and found that the BBS was unable to distinguish between children with mild balance deficits and children with no motor impairment. Their results suggested that the BBS has limited use for children with mild balance impairments due to a potential ceiling effect. We also found that the PBS might have limitations for use in children with mild balance impairments due to the same potential ceiling effect identified with the BBS.
In this study, no significant differences in DB were found between boys and girls. This finding is consistent with data reported by Williams et al,23 in which no significant difference in DB occurred between female and male children aged 3 to 9 years. Donahoe et al21 also discovered that gender did not account for additional variance in FRT scores in boys and girls aged 5 to 15 years. Although Largo et al17 observed no significant differences between boys and girls aged 5 to 18 years in timed performance of DB, Habib et al22 identified significant differences in balance abilities of female and male Pakistani children aged 5 to 13 years. Habib et al22 also found that socioeconomic status played an important role in some of the gender differences. Overall, boys performed better than girls on the TUG test, regardless of socioeconomic status, and in the lower socioeconomic status no significant difference occurred between boys and girls on the FRT.22 Nolan et al4 measured center of pressure movement in 9- to 16-year-old youth and reported that boys exhibited greater movement at 9 to 10 years, suggesting postural control in girls matured earlier than in boys. Franjoine et al33 also found that girls outperformed boys on the PBS, particularly in children 4 years and younger.
In addition to age, anthropometric factors were observed to influence balance performance in this study. Age was the strongest factor in predicting DB overall, accounting for 24% of the variance on the TUG test and 25% on the PBS. Conversely, arm length was the strongest predictor for reach balance activity, accounting for 47% of the variance on the PRT. Habib and Westcott24 determined that age was important in predicting TUG test scores; however, height was a stronger predictor of scores in children aged 5 to 7 years and 11 to 13 years with a high correlation occurring between height and age. Donahoe et al21 reported that age alone accounted for 38% of the variance in the FRT scores in American children aged 5 to 15 years. Habib and Westcott24 found that age accounted only for 17% of the variance in FRT scores in Pakistani children, with an additional 15% of the variance due to height, weight, and base of support. Arm length was not examined in their study, but in 8- to 10-year-old children, base of support was a significant predictor of mean FRT scores.24 Norris et al25 examined 3- to 5-year-old children and determined weight to be the only anthropometric factor to predict FRT scores for 3- and 4-year-old children, but no factors predicted FRT scores for the 5-year-old group. Duncan et al26 reported an association between arm length and functional reach.
Some differences between this study and prior research are likely due to the absence of age, arm length, or foot length as covariates in the analysis of anthropometric factors' effect on balance in previous studies. In this study, correlations were especially high between height, arm length, and foot length, with the highest correlation between height and arm length. Although arm length was found to be the strongest predictor of the PRT score, height and foot length are also factors potentially affecting reach. As with increasing age, height, weight, arm length, and foot length increase. Therefore, when age is observed to be the strongest predictor of TUG test and PBS scores, the identified anthropometric factors may also play a role in these scores.
Our findings suggest that DB ability is directly influenced by age. Older children demonstrated greater balance abilities than younger children measured on the TUG test, PBS, and PRT. Gender did not seem to influence the scores. The PBS appeared to measure differences in balance abilities in the younger children (5-7 years) but not in older children (8-12 years), indicating that a ceiling effect of the instrument for older ages. Although anthropometric variables were related to balance performance, age had the strongest relationship with outcomes on the TUG test and PBS, whereas arm length had the strongest relationship with outcomes on the PRT.
Use of a nonrandomized sample limits the generalizability of these data. The correlational design focused on relationships among age, gender, and DB but did not allow for predictions and determination of the most appropriate balance measure for children. Correlations can reveal only the relationships between the variables of age and gender with DB. The PBS has not yet been validated for the pediatric population, and no reference standard balance measurement is currently available for children.
Researchers should continue to investigate the use of the PRT and PBS in children and compare performance on the FRT and BBS to determine which tests are more applicable for pediatric use. The PRT and PBS could be expanded to determine sensitivity to change and minimal clinically important difference. In the future, normative data should be collected on the PRT, and additional normative data for children should be collected on the TUG test and PBS. A future study could expand to include children with different Gross Motor Function Classification system levels of CP, as Kembhavi et al34 did with the BBS. This future research involving children with CP could analyze the effectiveness of pediatric balance measures in detecting balance difficulties and determine the effects of their anthropometric characteristics on balance outcomes.
The PBS, PRT, and TUG test are reliable and easy to use without specialized equipment for assessing DB with children aged 5 to 12 years. Unlike the TUG test and PRT scores, which generally improve with increasing age through the age of 12 years, the PBS appears to plateau near the age of 8 years. More variability exists in the PRT than in the TUG test, but boys and girls perform similarly on each of the 3 tests.
Our findings may help pediatric physical therapists select a DB test according to age, rather than by specific diagnosis or gender. This decision may be particularly important for children with mild motor impairments and nonspecific diagnoses. For example, it might be more appropriate for a therapist to select the TUG test or PRT for a child older than 8 years. Given the ease of use and short duration of testing, the TUG test might be selected before the PRT. The PBS has a greater number of balance items addressed in the testing than the TUG test and PRT and might provide a wider range of balance information for a child younger than 8 years.
We thank the children and parents who participated in this study and the numerous community schools and clinic sites who allowed us to use their facilities. We appreciate the hard work and dedication of the research assistants in the data collection phase of this research.
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