Performance on the star excursion balance test predicts functional turnout angle in pre-pubescent female dancers.
Turnout is one of the most important cornerstones of ballet technique and is the basis for many other dance movements. Turnout is a movement pattern that is constrained by bony anatomy, ligamentous and capsular flexibility, and muscular strength and control. (5) There is no universally accepted operational definition of turnout. (6) However, many dance instructors and researchers describe an "ideal turnout" posture as one in which both of the lower limbs externally rotate 90[degrees], so that the feet form an angle of 180[degrees]. (4,7-9) Others describe this as an unrealistic expectation. Howse and McCormack, (5) for example, suggest that at this angle the feet are in an overly turned out position that is physically impossible to control; they propose a turnout angle of 140[degrees] as a position that allows for appropriate control in a strong and flexible hip. It is generally understood that turnout should originate primarily from the hip, but if the dancer does not have adequate range of motion at the hip, he or she may compensate at other links along the kinetic chain to produce the desired foot position. Such deficits in turnout angle and the incorrect movement patterns they produce have the potential to increase risk for injury. (4,5)
There is no standardized method for measuring turnout in dancers, and controversy within the dance medicine and science community has resulted in variability among research methodologies. (6) Turnout can be measured in a standing position using the functional turnout angle (FTA), as described by Negus. (9) This has been found to be a reliable method of measurement in an 18-to 22-year-old age cohort.
Screening tools are often used to identify athletes at risk for injury during sports participation. A variety of such tools are currently described in the literature. One example is the Star Excursion Balance Test SEBT). The SEBT measures dynamic standing balance under specific conditions and requires lower extremity coordination, flexibility, and strength. It has been used with dancers as a preliminary balance screen but has not been described as an injury screening tool. (10)
The purpose of this study was to determine the predictive relationship between performance on an injury screening tool, the SEBT, and a traditional performance measure, FTA, in pre-pubescent female dancers. A relationship between these measures may suggest a link between those who lack the ability to execute the turnout position successfully and those who are at risk for future injury. The investigators hypothesized that performance on the SEBT would fied Pubertal Maturational Observational Scale. (12,13) Exclusionary criterion was any lower extremity injury that would limit participation in dance class or in the study.
Prior to testing all subjects and their parent or guardian signed an informed assent and consent form, respectively, approved by the investigators' Institutional Review Board. Each dancer or her parent also completed a parental questionnaire on pubertal characteristics related to growth and development, a dance and sport participation intake form, and an injury questionnaire. The dancers then underwent anthropometric assessment of height, mass, and limb length. Each subject's limb length measurements were recorded on both legs as the most distal end of the anterior superior iliac spine to the most distal end of the lateral malleolus. The dancers then completed the SEBT and FTA assessments. The testing procedure was performed in a laboratory setting without mirrors or any other equipment typically found in a dance studio predict FTA in pre-pubescent female dancers.
Ten female pre-pubescent dancers with no previous history of lower extremity injury were recruited for this study. The subjects were recreational dancers from local dance studios in a large urban area. Their mean age was 7.3 years (range: 5 to 9 years), height 128.18 cm [+ or -] 12.5, weight 26.8 kg [+ or -] 7.25, and average body mass index 16 [+ or -] 2.2 (which is considered to be within normal range for children). (11) The subjects participated in dance for an average of 2.9 [+ or -] 1.5 hours per week, with an average dance experience of 3.4 [+ or -] 1.3 years. Eight out of 10 dancers took ballet class exclusively, while the remaining two participated in a combination of ballet, tap, and jazz.
Participants were included in the study if they were classified as pre-pubertal, had no current lower extremity injury that limited dance participation, and had taken any form of dance class within the past 6 months. Pre-pubertal status was determined using the modified Pubertal Maturational Observational Scale. (12,13) Exclusionary criterion was any lower extremity injury that would limit participation in dance class or in the study.
Prior to testing all subjects and their parent or guardian signed an informed assent and consent form, respectively, approved by the investigators' Institutional Review Board. Each dancer or her parent also completed a parental questionnaire on pubertal characteristics related to growth and development, a dance and sport participation intake form, and an injury questionnaire. The dancers then underwent anthropometric assessment of height, mass, and limb length. Each subject's limb length measurements were recorded on both legs as the most distal end of the anterior superior iliac spine to the most distal end of the lateral malleolus. The dancers then completed the SEBT and FTA assessments. The testing procedure was performed in a laboratory setting without mirrors or any other equipment typically found in a dance studio setting. Subjects did not warm-up prior to testing.
Star Excursion Balance Test
Each dancer completed a modified SEBT according to the methodology described by Plisky and coworkers. (14) This test has been shown to be reliable in the high school population, with an intraclass correlation coefficient (ICC) of 0.67 to 0.96, and may serve as a predictive measure for lower extremity injury. (14,15) Subjects all received verbal instruction and visual demonstration of the SEBT from the same examiner (Fig. 1). Each dancer stood on one leg, with the most distal aspect of her great toe on the center of the grid. Subjects were asked to reach with the free limb in three directions: anterior, posteromedial, and posterolateral. Six practice trials were performed on each limb for each of the three reach directions. On the seventh trial, the tester observed and recorded the maximal reach distance, in centimeters, in each direction, which was used for data analysis. The data collection trial was repeated if unilateral stance was not maintained throughout, the heel of the stance foot left the ground, the reach foot touched down, or the reach foot did not return to the start position. The process was then repeated with the subject standing on the other leg. The order of limb testing was counterbalance-randomized by the tester. The dominant limb was determined by asking the subject which foot she would use to kick a ball. A composite reach score for the SEBT was calculated by dividing the sum of the maximal distance reached in the anterior (A), posteromedial (PM), and posterolateral (PL) directions by 3 times the limb length (LL), and then multiplying by 100; Composite Reach Score = (A + PM +PL)/ (LL x 3) x 100.
Functional Turnout Angle
Functional turnout angle is defined as the angle that is formed by the longitudinal bisection of the feet with the dancer in first position. (4,9) For this study, each subject's FTA was measured as described by Negus, (9) that is:
1. The dancer stood on a piece of paper and rotated her lower extremities outward; she was cued to stand in first position as she would in a normal dance class, and was given no technique instructions or corrections.
2. The tester then traced around the subject's feet.
3. The longitudinal axis of each foot was drawn onto each tracing through the center of the rearfoot and forefoot; the midpoint of the heel was used as the landmark for the center of the rearfoot, and the extension of a longitudinal line originating at the midpoint of the second toe was used to demarcate the center of the forefoot.
4. This longitudinal line from the midpoint of the second toe to the midpoint of the heel was extended posteriorly until the lines from each foot intersected
5. The angle of bisection between these two longitudinal lines was measured by the tester, using a universal goniometer (Fig. 2).
One practice trial was performed, followed by three test trials. The mean of the three trials was then recorded as the FTA. Negus and coworkers reported excellent reliability for the FTA in a pre-professional population, with an intraclass correlation coefficient of 0.82. (9)
Simple linear regression was used to determine if there was a relationship between performance on the SEBT and FTA in this cohort.
The participants presented with a mean FTA ([+ or -] standard deviation) of 90.3[degrees] [+ or -] 17.7[degrees].
Composite reach performance on the SEBT, normalized to leg length, was assessed bilaterally for each dancer. The mean composite reach on the dominant limb for all participants ([+ or -] SD), normalized to leg length, was 81.4% [+ or -] 11.1%. Mean performance on the non-dominant limb was 81.9% [+ or -] 10.8% of the leg length. Simple linear regression demonstrated that SEBT performance on the dominant limb was a significant predictor of FTA (p = 0.02), with an [r.sup.2] = 0.49 Fig. 3). SEBT performance on the non-dominant limb demonstrated a trend toward prediction of FTA (p = 0.07), with [r.sup.2] = 0.35.
The investigators hypothesized that there would be a predictive relationship between composite reach score on a functional screening test, the SEBT, and functional turnout angle in pre-pubescent female dancers. This study indeed found that performance on the SEBT was predictive of FTA on the dominant limb. On the non-dominant limb there was a trend toward prediction. These findings indicate that pre-pubescent dancers who present with decreased FTA should be considered for SEBT screening to identify those who may be at increased risk for lower extremity injury.
Specific thresholds have been developed to screen for injury risk using the SEBT in sports such as basketball. Plisky and colleagues (14) found that high school female athletes with less than 94% composite reach on the SEBT were upwards of six times more likely to experience a lower extremity injury. In the current study, the composite reach for the dominant and non-dominant limb was 81.4 [+ or -] 11.1% and 81.9 [+ or -] 10.8%, respectively. These values are below the threshold of 94%, suggesting that these dancers may well be at increased risk of injury. However, the dancers in this study were significantly younger than the athletes studied by Plisky, and it is unknown if Plisky's normative values can be generalized to a younger athletic population. Hence, this comparison should be interpreted with caution.
The mean FTA (approximately 90[degrees]) in the current study was decidedly lower than that in most previous studies. Gilbert (8) had similar results, with a mean of 93.6[degrees] in 11 to 14-year-old girls, but those dancers were cued for correct alignment. Coplan and associates 4 found a mean of 109.2[degrees] in female college dancers (mean age: 22 years), while Negus and coworkers 9) found a mean of 131.4[degrees] in 18- to 22-year-old female dancers. Both protocols were similar to that used in this study, with the dancers cued to assume the first position they typically used in ballet class; however, dancers in those studies were significantly older than the present cohort, as they represented college or professional levels.
Young dancers are generally relative novices, which may affect their FTA. In addition, ongoing bony development between the acetabulum and the femur in these young dancers may have limited their ability to achieve a greater FTA. Bennell and colleagues (7) found that pre-pubertal girls, specifically, lack the full active hip range of motion needed to achieve ideal turnout.
The results of previous studies indicate that the relationship between FTA and SEBT is not related to an athlete's strength. Thorpe and associates (16) found that isolated hip, knee, and ankle strength measures did not affect SEBT scores. In addition, Robinson and Gribble (17) suggested that improvements on the SEBT were not due to strength or core stability but rather to increased knee and hip flexion on the stance limb. Conversely, Filipa and coworkers (18) found that a neuromuscular training program that focused on lower extremity strength and core stability improved composite SEBT scores in female soccer players. These findings suggest that FTA could be influenced by a similar training program in young dancers, which may be a useful direction for future research.
Interestingly, factors that could influence dancers' FTAs may not directly correlate with their performance on the SEBT. When forming the FTA, the dancer is able to compensate for a lack of hip rotation by using friction from the floor in a double-limb position to produce additional turnout at the lumbar spine, knee, foot, or ankle. The single-limb parallel position used during the SEBT does not require the dancer to go through active hip external range of motion; therefore, she is unable to compensate in the same manner as for the FTA. This indicates that the SEBT may be a good screening tool for determining if a dancer is at increased risk for injury because the SEBT does not allow the dancer to use compensations that may typically be used in ballet class to achieve ideal turnout.
Research is beginning to emerge among dance medicine specialists regarding how best to utilize the SEBT in dancers. Batson and colleagues (10) used a modified SEBT to assess dynamic balance and identify balance deficits in dancers with a history of LE injury. The results of this study advocate for the use of the SEBT as a functional screening tool, whereas Batson suggests its use as a test for balance.
One obvious limitation of this study is the relatively small sample size. Future investigations should validate these results in larger, more age-diverse dance populations.
Another limitation is lack of data on such biomechanical factors as the dancers' hip, knee, and ankle range of motion. Such variables may well have impacted each participant's performance on the composite reach score. For example, performing the SEBT with an extended knee could reduce the achievable reach distance. As previously noted, the dancers may have compensated elsewhere along the kinetic chain for limited range of motion at the hip to achieve a greater FTA. In future studies, researchers should devise methods to monitor for compensations of this sort that may skew their results.
We do not know conclusively that these dancers achieved their maximal FTA, even though several trials were taken. Future investigations should consider whether additional cuing at the time of testing affects the dancers' ability or willingness to achieve maximal FTA.
The current preliminary results indicate that young dancers who present with deficits in FTA should also be screened using the SEBT to determine their risk for lower extremity injury. The accessibility of these tests makes them desirable choices as screening tools for health care providers treating this population. Further research is warranted to validate the relationship between these tests, including when they are used with adolescent, pre-professional, and professional dancers.
Caption: Figure 1 Dancer performing the SEBT.
Caption: Figure 2 Functional turnout angle measurement.
Caption: Figure 3 Linear regression of SEBT of dominant limb and FTA.
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Alyson R. Filipa, P.T., D.P.T., M.S., S.C.S., C.S.C.S., is at the Cincinnati Children's Hospital Medical Center, Division of Occupational and Physical Therapy, Cincinnati, Ohio. Teresa R. Smith, P.T., D.P.T., C.S.C.S., is at the Cincinnati Children's Hospital Medical Center, Division of Occupational and Physical Therapy, Cincinnati OH, KORT Goss Ave Physical Therapy, Louisville, Kentucky. Mark V. Paterno, P.T., Ph.D., S.C.S., A.T.C., is at the Cincinnati Children's Hospital Medical Center, Division of Occupational Therapy and Physical Therapy, Sports Medicine Biodynamics Center at Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine Department of Pediatrics, Cincinnati, Ohio. Kevin R. Ford, Ph.D., F.A.C.S.M., is at the High Point University, High Point, North Carolina, Sports Medicine Biodynamics Center at Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine Department of Pediatrics, Cincinnati, Ohio. Timothy E. Hewett, Ph.D., F.A.C.S.M., is at the Ohio State University Sports Health and Performance Institute, Columbus, Ohio; and in the Sports Medicine Biodynamics Center at Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
Correspondence: Alyson R. Filipa, P.T., D.P.T., M.S., S.C.S., C.S.C.S., Cincinnati Children's Liberty Campus, 7777 Yankee Road, MLC 16016, Liberty Township, Ohio 45044; firstname.lastname@example.org.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Author:||Filipa, Alyson R.; Smith, Teresa R.; Paterno, Mark V.; Ford, Kevin R.; Hewett, Timothy E.|
|Publication:||Journal of Dance Medicine & Science|
|Date:||Oct 1, 2013|
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