RELATIONSHIPS BETWEEN LOWER-EXTREMITY FLEXIBILITY, ASYMMETRIES, AND THE Y BALANCE TEST GRANT V. OVERMOYER1
AND
RAOUL F. REISER II,1,2
1
Clinical Biomechanics Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, Colorado; and 2School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado
ABSTRACT Overmoyer, GV and Reiser II, RF. Relationships between lower-extremity flexibility, asymmetries, and the Y Balance Test. J Strength Cond Res 29(5): 1240–1247, 2015—Joint flexibility, bilateral asymmetries in flexibility, and bilateral asymmetries in performance of the Y Balance Test have been associated with injuries. However, relationships among these attributes are unclear. The goal of this investigation was to examine how flexibility and flexibility asymmetries relate to the Y Balance Test. Twenty healthy active young adults (9 men and 11 women; mean 6 SD: age = 21.9 6 2.6 years; height = 171 6 8.8 cm; mass = 67.2 6 1.9 kg) performed 9 different lower extremity active range of motion (AROM) tests and the Y Balance Test in a single visit. Significant correlations (p # 0.05) existed between bilateral average AROM measures and bilateral average Y Balance Test scores at the ankle and hip. Specifically, ankle dorsiflexion AROM at 08 knee flexion significantly correlated with Anterior, Posterolateral, and Composite directional scores of the Y Balance Test (r = 0.497–0.736). Significant correlations in ankle dorsiflexion AROM at 908 knee flexion also existed with Anterior, Posterolateral, Posteromedial, and Composite directional scores (r = 0.472–0.795). Hip flexion AROM was significantly correlated with Posterolateral, Posteromedial, and Composite directional scores (r = 0.457–0.583). Significant correlations between asymmetries in AROM and asymmetries in the Y Balance Test existed only in ankle plantarflexion with Anterior, Posterolateral, and Composite directional scores of the Y Balance Test (r = 0.520–0.636). Results suggest that when used with recreationally active healthy adults, the Y Balance Test may help identify lowerextremity flexibility deficits and flexibility asymmetries in the ankle and hip regions but may need to be used in conjunction
Address correspondence to Raoul F. Reiser II, [email protected]. 29(5)/1240–1247 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
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with additional tests to understand a broader picture of functional movement and injury risk.
KEY WORDS Star Excursion Balance Test, bilateral asymmetry, active range of motion, injury risk, performance
INTRODUCTION
F
lexibility (also known as range of motion [ROM]) is typically considered a necessary component of sport and fitness (13). Lower-extremity flexibility, specifically, has been shown to be important for successful performance of sport movements (7) and activities of daily life (2,8). Beyond flexibility for function, flexibility is an essential factor for reducing injury risk (16,22). Side-toside symmetry in flexibility is also likely to be an important aspect of performance and injury prevention (1,3,6,14). The goniometer is arguably the most common and validated tool for measuring joint ROM (18). However, goniometry can be difficult to master and time consuming to complete on multiple joints and multiple axes within a joint. This makes comprehensive ROM assessment difficult when screening large groups of athletes. Furthermore, goniometers only measure ROM without simultaneously capturing other potential factors affecting injury or performance. Considering this, alternative screening methods could prove useful under many circumstances. One possible test that fits these criteria is the Star Excursion Balance Test (SEBT). The SEBT is a dynamic balance test requiring multiple reaches (also known as excursions) with 1 foot in a star-like pattern while maintaining balance on the stance leg. The Y Balance Test, or more simply the Y-Test, involving excursions in just 3 directions (anterior, posterolateral, and posteromedial) is becoming a commonly used more refined version of the traditional 8 excursion SEBT. The Y-Test is relatively inexpensive, portable, and easy to administer and does not require much specialized training but still shows good repeatability (see Ref. 9 for review). The 3 excursions of the Y-Test have been effectively used to screen for risk of injury or reinjury and injury risk related to asymmetry (see Ref. 9 for review). Furthermore, lowerextremity ROM has been shown to be a factor contributing
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Journal of Strength and Conditioning Research to larger excursion scores (11,21). The Y-Test may conceivably also measure the net effect of flexibility from 1 joint to the other, potentially serving as both an assessment of some types of active range of motion (AROM) and functional flexibility. Finally, the Y-Test has been effectively used to screen for lower-extremity asymmetry (20). Because flexibility is a potential element of asymmetry, the Y-Test may help assess side-to-side flexibility differences as well. Therefore, the Y-Test may serve as an alternative to less convenient and perhaps less comprehensive tests such as ROM measures using the goniometer. The goals of this investigation were to identify the correlations between bilateral flexibility in lower-extremity AROM measurements with bilateral performance in the YTest, in absolute terms (i.e., regardless of side-to-side asymmetry), and explore the relationship between lowerextremity asymmetries in AROM in comparison with asymmetries in Y-Test performance in a healthy young adult population. It was hypothesized that larger values of bilateral AROM would relate to larger excursion scores bilaterally on the Y-Test and higher levels of side-to-side asymmetry in AROM measures would relate to higher asymmetry in YTest scores. The results of this study will serve to develop a practical understanding of the relationships between flexibility and performance on the Y-Test in both absolute terms and flexibility relative to the contralateral limb, with the ultimate goal of improving screening methods for injury risk and performance.
METHODS Experimental Approach to the Problem
To accomplish the goals of this investigation, a cross-sectional research design was used. Healthy, active, pain-free subjects
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with limited previous injury were recruited. A population of healthy adults was used because it has previously been demonstrated that measurable asymmetry exists even in healthy people with no known reasons for being asymmetric (12,14,20). During a single visit lasting approximately 2 hours, subjects performed in order the Y-Test, a battery of 9 AROM measures, and 4 functional movements after adequate warmup and practice. The relationships between ground reaction force asymmetries during the functional movements (standing, bodyweight squats, countermovement jumps, and singleleg drop landings) and the Y-Test are presented elsewhere (19). Approximately half of the subjects returned for a second visit to repeat the measures. To test the proposed hypotheses, relationships between measures were assessed through correlations. Specifically, average bilateral AROM measurements were correlated to average bilateral Y-Test scores, and Y-Test excursion direction asymmetries were correlated to AROM asymmetries. Intraclass correlations were used to assess the repeatability of measures within those who returned for the repeat visit. Subjects
Twenty (9 men and 11 women) nonobese (body mass index ,30 kg$m22) healthy individuals aged 19–30 years (Table 1) participated after initial screening by a brief health and activity questionnaire. All subjects granted university’s Institutional Review Board–approved written informed consent after having the study explained to them. Subjects were identified as individuals who were currently recreationally active and were not specifically drawn from an athlete population. To meet inclusion criteria, recreational activities had to include jumping and squatting type movements. These movements were selected because of their high prevalence in exercise and sport along with their lower-extremity joint
TABLE 1. General subject characteristics.* Men (n = 9)
Age (y) Height (m) Mass (kg) BMI (kg$m22) Anatomical leg length NKL (cm) Anatomical leg length KL (cm) Anatomical LLD NKL-KL (cm) Absolute anatomical LLD (cm) Bilateral average leg length (cm) Functional LLD NKL-KL (cm) Absolute functional LLD NKL-KL (cm)
Women (n = 11)
Whole group (n = 20)
Mean
SD
Mean
SD
Mean
SD
a
22.3 1.8 74.6 23.5 97.2 96.2 1.0 1.3 96.7 0.2 0.4
1.4 0.1 4.8 1.7 3.5 3.8 1.2 0.8 3.6 0.5 0.3
21.6 1.7 61.2 22.4 88.2 87.4 0.8 0.9 87.8 20.1 0.1
3.4 0.1 5.3 2 3.7 3.8 1.0 0.8 3.7 0.2 0.2
21.9 1.71 67.2 22.9 92.2 91.4† 0.9 1.1 91.8 0.0 0.3
2.6 0.09 1.9 1.9 5.7 5.8 1.1 0.8 5.8 0.4 0.3
1.000 0.998 0.997 0.997 0.997 0.865 0.747 0.998 0.765 0.444
*a = Cronbach’s alpha for returning subjects; BMI = body mass index; NKL = non–kicking leg; KL = preferred kicking leg; LLD = leg length difference. †p , 0.01 between NKL and KL in whole group.
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Flexibility Asymmetries patterning relative to the Y-Test. Furthermore, to be considered recreationally active, subjects must have been involved in activities requiring these movement patterns at least once per week for the past 8 weeks based on self-report/recall. Recreational activities included, but were not limited to, resistance training, step aerobics, basketball, racquetball, baseball, and soccer. Although many recreational activities require a strong element of balance, no subjects were known to have prior exposure to the Y-Test or specific dynamic balance training, which might interfere with the validity of the testing protocol. Other exclusion criteria included self-reported pain, injury, or soreness to the lower back or lower extremities at the time of the visit. Any injuries must have healed with a return to regular activity at least 4 weeks before participation. Those with a history of back or lower-extremity pain, major previous surgery, bone, joint, or muscular disorder, history of neurological/orthopedic dysfunction, or pain that would limit the ability to perform functional tasks correctly were excluded. Any subjects with a known reason to perform these activities asymmetrically for anthropometric or orthopedic reasons were also excluded (e.g., known limb-length discrepancy, bilateral corrective devices, braces, anterior cruciate ligament tear/reconstruction, chronic ankle sprains, etc.). Pregnant women were also excluded.
Procedures
All subjects completed the initial visit to the laboratory, with 11 subjects returning a second time for the repeatability assessment (at least 2 days after the initial visit but no later than 31 days). Subjects were instructed to abstain from heavy exercise of the lower limbs and back for 48 hours before the visit and to limit exercise to normal daily activities for the lower extremities the day before and day of testing. Caffeine consumption was limited to normal daily intake, and no other ergogenic aids were allowed for consumption during the prior 24 hours leading up to the visit. It was confirmed before testing that subjects felt that they were under a normal physical and mental state without influence by a significant change in sleep, nutrition, or alcohol consumption the day of or the day preceding testing. Requirements and procedures of the second visit were identical to the initial visit. Retesting was performed at a similar time of day relative to the initial visit. After arriving and verifying eligibility, subjects were given orientation to the laboratory followed by measurement of body weight and height without shoes. Subjects wore clothing appropriate for physical activity (e.g., t-shirts and shorts). A warm-up of no less than 5 minutes on a stationary cycle ergometer was required for all subjects. Stretching was
TABLE 2. AROM measures performed (listed in order of execution top to bottom). Movement
Body position*
Hip flexion
Supine, straight knee
Hip extension
Prone, straight knee
Hip abduction
Fulcrum†
Proximal goniometer arm Midline of the upper body
Head of the fibula
Midline of the upper body
Head of the fibula
Contralateral ASIS
Inferior aspect of the ipsilateral patella Inferior aspect of the ipsilateral patella Center point midway between the 2 malleoli of the ankle Center point midway between the 2 malleoli of the ankle Lateral aspect of the fifth metatarsal Lateral aspect of the fifth metatarsal Lateral aspect of the fifth metatarsal
Supine, straight knee
Greater trochanter of the femur Greater trochanter of the femur Ipsilateral ASIS
Hip adduction
Supine, straight knee
Ipsilateral ASIS
Contralateral ASIS
Hip internal rotation
Seated, both knees bent at 908, lower legs hanging from measuring surface
Inferior aspect of the patella
Perpendicular to the floor
Hip external rotation
Seated, both knees bent at 908, lower legs hanging from measuring surface
Inferior aspect of the patella
Perpendicular to the floor
Ankle plantarflexion Ankle dorsiflexion 08 Ankle dorsiflexion 908
Supine, straight knee
Lateral malleolus Lateral malleolus Lateral malleolus
Head of the fibula
Supine, straight knee Supine, knee bent to 908
Distal goniometer arm
Head of the fibula Head of the fibula
*If not listed, body is assumed to be in neutral position. †Goniometer fulcrum was always aligned on the center of the landmark listed. ASIS = anterior-superior iliac spine.
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Journal of Strength and Conditioning Research not allowed at any point during the study to avoid confounding factors, which might be caused by stretching 1 side more vigorously than the other. After the warm-up, functional leg length asymmetry and anatomical leg length measurements were taken with the subject in the supine position on an elevated examination table as described by Hinson and Brown (10) and Evans (5), respectively. Briefly, functional leg length asymmetry is a measurement of the distance one limb protrudes relative to the other when lying relaxed, whereas anatomical leg length is a boney measure from the anterior-superior iliac spine to the medial malleolus. Functional and anatomical measurements were taken
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twice with the left side always measured first during the anatomical measurement, and the average of 2 measurements was used for analysis. The Y-Test was then performed in stocking feet as described by Plisky et al. (20) in the 3 common excursion directions: to the front (Ant), diagonally back and to the medial side of the reaching leg (PostMed), and diagonally back and to the lateral side of the reaching leg (PostLat). The distal aspect of the subject’s great toe was centered at the junction of the Y, which was outlined on the floor with secured inextensible tape measures (19). The subject performed a reach in all 3 directions on the left foot
TABLE 3. AROM descriptives (8).* Men (n = 9)
Hip flexion Bilateral Avg NKL-KL Abs NKL-KL Hip extension Bilateral Avg NKL-KL Abs NKL-KL Hip abduction Bilateral Avg NKL-KL Abs NKL-KL Hip adduction Bilateral Avg NKL-KL Abs NKL-KL Hip internal rotation Bilateral Avg NKL-KL Abs NKL-KL Hip external rotation Bilateral Avg NKL-KL Abs NKL-KL Ankle plantarflexion Bilateral Avg NKL-KL Abs NKL-KL Ankle dorsiflexion 08 Bilateral Avg NKL-KL Abs NKL-KL Ankle dorsiflexion 908 Bilateral Avg NKL-KL Abs NKL-KL
Women (n = 11)
Whole group (n = 20) a
Mean
SD
Mean
SD
Mean
SD
62 22 4
11 4 3
78 2 5
15 6 4
71 0 4
15 5 4
0.988 0.841 0.656
22 1 4
7 5 3
23 21 3
4 3 1
23 0 3
5 4 2
0.758 0.525 0.694
32 1 2
3 3 2
36 21 4
6 5 3
34 0 3
6 4 2
0.975 20.086 20.587
12 1 3
3 4 2
18 0 3
3 4 2
15 0 3
4 4 2
0.789 0.869 0.778
28 21 3
4 3 2
33 22 3
5 3 3
31 22† 3
5 3 2
0.953 0.905 0.795
28 2 4
4 4 3
31 2 3
5 3 2
30 2† 3
5 3 2
0.833 0.764 0.112
74 2 2
8 3 2
79 0 2
5 3 2
77 1 2
7 3 2
0.946 0.877 0.910
75 21 3
4 4 2
74 22 3
5 3 2
74 21 3
4 3 2
0.958 0.548 0.312
80 2 5
5 6 4
78 21 3
6 4 2
83 0 4
5 5 3
0.875 0.802 0.590
*a = Cronbach’s alpha for returning subjects; NKL = non–kicking leg; KL = kicking leg; Abs = absolute; AROM = active range of motion; Avg = average. †p # 0.05 between NKL and KL in whole group.
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Flexibility Asymmetries (Ant, PostMed, and then PostLat), followed by all 3 on the right foot. This was then repeated for a total of 6 correct practice trials. A correct trial required the heel of the plant foot to stay in contact with the ground, the hands remained on the hips at all times, the subject lightly brushed the measuring tape at the furthest point possible without planting weight onto the reaching foot, and the subject recovered to a single-leg standing position for at least 2 seconds. After the 6 practice trials, 3 more correct trials for which data were recorded completed in the same manner. The researcher visually identified the furthest point reached on the tape measure. A fourth or fifth trial was granted if excursion distance appeared to still be improving. The process of each AROM measurement was described to the subject and then performed as described by Norkin and White (18). However, unlike Norkin and White, measurements were conducted with the subject actively moving the joint in the specified direction, instead of being passively moved by the researcher (Table 2). The joint position was held for approximately 5–10 seconds while a measurement was taken with a universal goniometer (Model 01135; Lafayette Instrument Co. Inc., Lafayette, IN, USA). Each AROM measure was performed first on the left and then on the right side, before moving on to the next measure. After all 9 measures were performed, each was performed again for a second time, using the average of the 2 measurements in the analysis. All AROM measures were performed by the same researcher.
each excursion direction was also analyzed, as well as a summed Composite score of the maximums for each lower extremity. To control for the effect of limb length between subjects, Y-Test values were normalized to percent of average anatomical limb length (average of the right and left sides). The normalized preferred kicking leg (KL) Y-Test score (reaching with KL) was subtracted from that when performed with the non–kicking leg (NKL) to quantify the presence of asymmetry (%NKL 2 KL). Active range of motion asymmetry values were calculated by taking the NKL angular position and subtracting the KL angle (NKL8 2 KL8). Bilateral averages for Y-Test scores and AROM scores were also calculated. This was performed by averaging the scores on each side for all 3 YTest excursions, the Y-Test Composite scores, and all 9 AROM measures. Statistical Analyses
Group mean values and SD were compiled for all variables. To show the overall magnitude of asymmetries, mean and SD of absolute levels of asymmetries were compiled along with the side-to-side (NKL-KL) difference. Paired t-tests were performed on all NKL vs. KL values to determine the existence of significant population-wide bilateral differences related to KL. Pearson’s correlations (r) were performed comparing bilateral average and asymmetry values in each AROM measure with each individual and combination of excursions in the Y-Test, as well as anatomical leg length differences. Intraclass correlations (Cronbach’s Alpha, a) were used to establish intersession repeatability of all measures reported. Finally, a or r , 0.500 were classified as weak, from 0.500 to 0.799 were classified as moderate, and $0.800 were classified as strong. Statistical analysis was conducted in IBM SPSS
Data Processing and Analyses
The Y-Test was analyzed using the average (Avg) of the last 3 trials for each reach direction for each lower extremity and the average of the total of the 3 reach directions (also known as Composite). The maximum (Max) value measured for
TABLE 4. Bilateral Avg AROM vs. Y-Test correlations (r) (n = 20).* Ant
PostLat
PostMed
Composite
Bilateral Avg
Avg
Max
Avg
Max
Avg
Max
Avg
Max
Hip Flex Hip Ext Hip Abd Hip Add Hip IR Hip ER Ankle PF Ankle DF 08 Ankle DF 908
0.411 0.037 0.347 0.264 0.124 0.124 20.211 0.736z 0.795†
0.347 0.012 0.301 0.234 0.076 0.065 20.230 0.706z 0.777z
0.457† 0.047 0.081 0.210 0.121 0.039 20.288 0.497† 0.650z
0.402 0.039 20.019 0.106 0.053 0.084 20.314 0.408 0.560†
0.583z 0.256 0.261 0.142 0.319 0.129 0.175 0.301 0.424
0.510† 0.275 0.182 0.079 0.293 0.148 0.118 0.320 0.472†
0.516† 0.106 0.211 0.191 0.219 0.120 20.102 0.540† 0.667z
0.490† 0.150 0.170 0.136 0.183 0.142 20.142 0.517† 0.665z
*AROM = active range of motion; Ant = anterior; PostLat = posterolateral; PostMed = posteromedial; Avg = average; Max = maximum; Flex = flexion; Ext = extension; Abd = abduction; Add = adduction; IR = internal rotation; ER = external rotation; PF = plantarflexion; DF = dorsiflexion. †p # 0.05 zp , 0.01
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TABLE 5. AROM asymmetries vs. Y-Test asymmetries correlations (r) (n = 20).* Ant
Hip Flex Hip Ext Hip Abd Hip Add Hip IR Hip ER Ankle PF Ankle DF 08 Ankle DF 908
PostLat
PostMed
Composite
Avg
Max
Avg
Max
Avg
Max
Avg
Max
0.238 0.097 20.049 20.067 0.149 0.032 0.565† 20.162 20.423
0.165 0.108 20.108 0.059 0.103 0.089 0.636z 20.192 20.288
0.041 0.156 0.001 0.121 20.142 20.086 0.520† 20.106 20.021
20.022 0.080 20.133 0.047 20.194 20.152 0.352 20.015 20.170
20.109 20.227 20.325 0.099 20.099 20.040 0.290 0.243 20.264
20.140 20.254 20.182 0.094 20.009 20.094 0.279 0.237 20.309
0.014 20.024 20.183 0.078 20.058 20.050 0.565z 0.043 20.297
0.015 20.026 20.144 0.094 0.053 20.049 0.439 0.108 20.391
*AROM = active range of motion; Avg = average; Max = maximum; Ant = anterior; PostLat = posterolateral; PostMed = posteromedial; Flex = flexion; Ext = extension; Abd = abduction; Add = adduction; IR = internal rotation; ER = external rotation; PF = plantarflexion; DF = dorsiflexion. †p # 0.05 zp , 0.01.
Statistics version 19.0 (Chicago, IL, USA) with significance set at p # 0.05.
RESULTS Eighteen of the 20 subjects indicated that the right leg was their KL and 2 indicated the left leg. General subject characteristics tended to be highly repeatable from day to day for the 11 subjects (6 women and 5 men) who returned for a second visit, except for absolute functional leg length difference (Table 1). Repeat visits averaged 19.0 6 9.5 days after the initial visit. Although small in magnitude, the anatomical leg length of the NKL was on average significantly longer than the KL. Small absolute levels of asymmetry, within 628 NKL-KL, existed in the AROM measures, although only hip internal and external rotations were statistically significant between limbs (Table 3). Active range of motion asymmetries typically exhibited moderate-to-strong repeatability, although hip external rotation and ankle dorsiflexion at 08 knee flexion both had poor repeatability in absolute measures, whereas hip abduction was the opposite with moderate repeatability in absolute measures and poor repeatability in relative measures (Table 3). Anatomical leg length difference did not significantly correlate with any of the AROM asymmetries. Y-Test results are detailed in the study by Overmoyer and Reiser (19). In brief, small absolute levels of bilateral differences in Y-Test scores existed, but none of the NKL vs. KL comparisons were statistically significant. Furthermore, individual leg and bilateral differences in Y-Test scores typically showed good repeatability, although absolute bilateral differences tended to be less repeatable than relative differences. The bilateral average AROM scores and bilateral average Y-Test scores had several significant correlations existing
between them (Table 4). The significant correlations in this comparison were weak to moderate but never strong. Significant findings included weak-to-moderate correlations in hip flexion AROM measures with Avg and Max PostMed, Avg and Max Composite scores, and Avg PostLat scores (r = 0.457–0.583). Significant weak-to-moderate correlations also existed in ankle dorsiflexion at 908 knee flexion with the Avg and Max Anterior, Avg and Max Posterolateral, Max PostMed, and Avg and Max Composite scores (r = 0.472– 0.795). Additionally, significant moderate correlations between ankle dorsiflexion at 08 knee flexion and both Avg and Max Anterior and Composite scores existed (r = 0.517– 0.736), while also showing a nearly moderate correlation when comparing ankle dorsiflexion at 08 knee flexion with Avg PostLat (r = 0.497). When comparing AROM asymmetries with Y-Test asymmetries, there were significant moderate correlations, but exclusively in ankle plantarflexion AROM (Table 5). This included ankle plantarflexion with Avg Ant, Max Ant, Avg PostLat, and Avg Composite (r = 0.565, 0.636, 0.520, and 0.565, respectively). Finally, anatomical asymmetries did not significantly correlate with Y-Test asymmetries except for a weak but significant inverse correlation with asymmetries in the Avg PostLat excursion (r = 20.459).
DISCUSSION Overall, our Y-Test scores were highly comparable with other studies as previously discussed in the study by Overmoyer and Reiser (19) with Y-Test asymmetries demonstrating good day-to-day repeatability as was expected (17,20). Bilateral averages for AROM measures were within expected ranges of healthy active adults (14,18). Small levels of asymmetries existed within this population during AROM VOLUME 29 | NUMBER 5 | MAY 2015 |
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Flexibility Asymmetries measurements, which is consistent with other studies (4,14) and when performing the Y-Test (20). The expression of AROM also showed good repeatability from day-to-day in most cases as expected (18). However, although AROM asymmetries were frequently highly repeatable, they exhibited low repeatability in some measures of some individuals. This day-to-day variability does not preclude the possibility that on any given day, AROM asymmetries could still be a risk factor or associated with other measures. Furthermore, the observed small differences in anatomical leg length do not appear to play an important role in any of the observed asymmetries. Therefore, the results are appropriate for addressing the proposed goals, which sought to explore how bilateral average AROM measures in these joint motions related to bilateral average Y-Test excursions and the relationships between asymmetries within lower extremity AROM and asymmetries in Y-Test performance in a healthy active population. The results when looking at relationships among AROM and the Y-Test relative to bilateral averages (i.e., not looking at side-to-side asymmetry) partially support our hypothesis. Dorsiflexion at both 08 and 908 knee flexion seem to be the most important factors when looking at flexibility’s role in YTest performance, especially in regard to the Ant excursions. This is likely emphasized in the Y-Test protocol used here where the heel was required to remain in contact with the floor, thus noticeably applying a stretch to the calf muscles during the Ant excursion. However, the PostLat direction also seemed to moderately rely on the dorsiflexion at 908 knee flexion ROM, which is not as easily explained with the heel on the ground protocol. Additionally, bilateral average hip flexion showed a moderate relationship with the PostMed excursion, which may point to this joint motion, playing an important role in performance during this excursion. The Composite Y-Test scores also showed significant correlations to these variables, but the correlations were not any stronger than the strongest of its constituent parts, meaning that these composite measures likely have less worth than looking at individual measures alone. Plisky et al. (20) reported that female high-school basketball players who had Composite reach distances under a certain threshold were 6.5 times more likely to have lower extremity injury over the course of the upcoming season. Although the population they used consisted of a younger and potentially more athletic group, it is possible, based on these data, that appropriate AROM in dorsiflexion and hip flexion may be a contributor to this higher injury rate. Because of only moderate correlations, this alone is unlikely to explain the majority of their findings, however. Furthermore, it has been suggested that tightness in the soleus and gastrocnemius, which would be stretched during dorsiflexion, may cause increased knee valgus (15), again relating to a higher level of injury risk (23). Therefore, it is possible that the Y-Test is picking up on this potential compensation, which may ultimately contribute to lower extremity injury.
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The results regarding asymmetries in AROM relative to asymmetries in Y-Test scores again partially support our hypothesis. Ankle plantarflexion seemed to be by far the biggest contributor to asymmetry in the Y-Test of all the AROM measures conducted. Plantarflexion asymmetry appears to contribute to Ant, PostLat, and Composite asymmetries. This suggests that the ability to point your toe may be a strong factor in asymmetry in excursion scores. This might be somewhat telling to the results of Plisky et al. (20) as well. Plisky et al. found that an Ant excursion asymmetry of more than 4 cm gave high-school basketball players a 2.5-fold increase in lower extremity injury risk. Our findings might suggest that asymmetry in plantarflexion has a role in this increased injury risk, although it is unclear how. Interestingly, plantarflexion did not play a role in bilateral Y-Test scores, having a weak and statistically insignificant relationship with all excursions (│r│ # 0.314). This might be because asymmetry scores tend to be small in magnitude compared with the overall Y-Test scores. Thus, a few degrees difference in plantarflexion asymmetry might have a significant effect on asymmetry scores but have an insignificant effect on overall Y-Test performance. Some limitations exist within the research design of this study. It is unknown whether being above or below a baseline threshold of flexibility or asymmetry might have a greater effect or if there is a threshold level of AROM that may relate to a more pronounced contribution to Y-Test scores. Within this study, this threshold, if it exists, could not be illuminated. Furthermore, the population examined here was overall active, young, and injury-free and therefore was unlikely to have very low levels of flexibility or high levels of asymmetry. Although it gives insight into a more fit and active population, this might contribute to a lower level of correlation in some cases than a population that has more reason to be asymmetric. With a more asymmetric subject pool, these correlations could have much more strength, but this is currently unknown. Additionally, no sex-specific analyses were performed. Although the majority of the literature does not support the need for this, there may be some rational for doing so in the Y-Test (see Ref. 9 for review). Because of this possibility, this is a subject requiring further research.
PRACTICAL APPLICATIONS In a young healthy population with no specific reasons to be highly asymmetric, the Y-Test data suggest that using the YTest as a screening method may be useful in exposing some lower-extremity flexibility asymmetries or bilateral deficits in flexibility. Of all the joint measures examined, ankle dorsiflexion and hip flexion are the primary AROM measures, which seem to contribute to the overall Y-Test scores. This seems consistent with the study by Robinson and Gribble (21) and Hoch et al. (11), which have previously suggested that these joint motions play an important role in SEBT or Y-Test performance. Additionally, side-to-side differences in
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Journal of Strength and Conditioning Research Y-Test scores may indicate asymmetries in ankle plantarflexion. However, Y-Test asymmetries seem unlikely to expose asymmetries in most lower extremity AROM measures and may therefore not be a good replacement for goniometer measures in many cases. Regardless, the Y-Test alone may be very good at exposing some flexibility asymmetries, although at this time, it appears unlikely to be able to capture the wide range that a battery of goniometer measures can. How groups/individuals with higher levels of asymmetries and specific differences between men and women need further exploration.
ACKNOWLEDGMENTS The authors would like to express their gratitude to the participants, as well as Hung Mai, Katelyn Walker, Kent Gneiting, and Katherine Brown, who freely volunteered their time toward this unfunded research project. The authors have no conflict of interest to declare nor do the results of this study constitute endorsement of any products by the authors or the National Strength and Conditioning Association.
REFERENCES 1. Baumhauer, JF, Alosa, DM, Renstrom, P, Trevino, S, and Beynnon, B. A prospective-study of ankle injury risk-factors. Am J Sports Med 23: 564–570, 1995. 2. Brito, LBB, de Araujo, D, and de Araujo, CGS. Does flexibility influence the ability to sit and rise from the floor? Am J Phys Med Rehab 92: 241–247, 2013. 3. Cibulka, MT and Threlkeld-Watkins, J. Patellofemoral pain and asymmetrical hip rotation. Phys Ther 85: 1201–1207, 2005. 4. Daneshjoo, A, Rahnama, N, Mokhtar, AH, and Yusof, A. Bilateral and unilateral asymmetries of isokinetic strength and flexibility in male young professional soccer players. J Hum Kinet 36: 45–53, 2013. 5. Evans, R. Illustrated Essentials in Orthopedic Physical Assessment. St. Louis, MO: Mosby, 1994. 6. Fousekis, K, Tsepis, E, and Vagenas, G. Intrinsic risk factors of noncontact ankle sprains in soccer a prospective study on 100 professional players. Am J Sports Med 40: 1842–1850, 2012.
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9. Gribble, PA, Hertel, J, and Plisky, P. Using the Star Excursion Balance Test to assess dynamic postural-control deficits and outcomes in lower extremity injury: A literature and systematic review. J Athl Train 47: 339–357, 2012. 10. Hinson, R and Brown, S. Supine leg length differential estimation: An inter- and intra-examiner reliability study. Chiropr Res J 5: 17–22, 1998. 11. Hoch, MC, Staton, GS, and Mckeon, PO. Dorsiflexion range of motion significantly influences dynamic balance. J Sci Med Sport 14: 90–92, 2011. 12. Hodges, SJ, Patrick, RJ, and Reiser, RF. Effects of fatigue on bilateral ground reaction force asymmetries during the squat exercise. J Strength Cond Res 25: 3107–3117, 2011. 13. Jeffries, I. Warm-up and stretching. In: Essentials of Strength and Conditioning (3rd ed.). T Baechle and R Earle, eds. Champaign, IL: Human Kinetics, 2008. pp. 295–324. 14. Knapik, JJ, Bauman, CL, Jones, BH, Harris, JM, and Vaughan, L. Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes. Am J Sports Med 19: 76–81, 1991. 15. Macrum, E, Bell, DR, Boling, M, Lewek, M, and Padua, D. Effect of limiting ankle-dorsiflexion range of motion on lower extremity kinematics and muscle-activation patterns during a squat. J Sport Rehab 21: 144–150, 2013. 16. Mann, KJ, Edwards, S, Drinkwater, EJ, and Bird, SP. A lower limb assessment tool for athletes at risk of developing patellar tendinopathy. Med Sci Sport Exerc 45: 527–533, 2013. 17. Munro, AG and Herrington, LC. Between-session reliability of the Star Excursion Balance Test. Phys Ther Sport 11: 128–132, 2010. 18. Norkin, CC and White, DJ. Measurement of Joint Motion: A Guide to Goniometry (4th ed.). Philadelphia, PA: F.A. Davis Company, 2009. 19. Overmoyer, GV and Reiser, RF. Relationships between asymmetries in functional movements and the star excursion balance test. J Strength Cond Res 27: 2013–2024, 2013. 20. Plisky, PJ, Rauh, MJ, Kaminski, TW, and Underwood, FB. Star excursion balance test as a predictor of lower extremity injury in high school basketball players. J Orthop Sports Phys Ther 36: 911– 919, 2006. 21. Robinson, RH and Gribble, PA. Kinematic predictors of performance on the Star Excursion Balance Test. J Sport Rehabil 17: 347–357, 2008.
7. Gleim, GW and Mchugh, MP. Flexibility and its effects on sports injury and performance. Sports Med 24: 291–301, 1997.
22. Steinberg, N, Siev-Ner, I, Peleg, S, Dar, G, Masharawi, Y, Zeev, A, and Hershkovitz, I. Extrinsic and intrinsic risk factors associated with injuries in young dancers aged 8-16 years. J Sports Sci 30: 485–495, 2012.
8. Goncalves, LC, Vale, RGD, Barata, NJF, Varejao, RV, and Dantas, EHM. Flexibility, functional autonomy and quality of life (QoL) in elderly yoga practitioners. Arch Gerontol Geriatr 53: 158–162, 2011.
23. Sutton, KM and Bullock, JM. Anterior cruciate ligament rupture: Differences between males and females. J Am Acad Ortho Surg 21: 41–50, 2013.
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AND
RAOUL F. REISER II,1,2
1
Clinical Biomechanics Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, Colorado; and 2School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado
ABSTRACT Overmoyer, GV and Reiser II, RF. Relationships between lower-extremity flexibility, asymmetries, and the Y Balance Test. J Strength Cond Res 29(5): 1240–1247, 2015—Joint flexibility, bilateral asymmetries in flexibility, and bilateral asymmetries in performance of the Y Balance Test have been associated with injuries. However, relationships among these attributes are unclear. The goal of this investigation was to examine how flexibility and flexibility asymmetries relate to the Y Balance Test. Twenty healthy active young adults (9 men and 11 women; mean 6 SD: age = 21.9 6 2.6 years; height = 171 6 8.8 cm; mass = 67.2 6 1.9 kg) performed 9 different lower extremity active range of motion (AROM) tests and the Y Balance Test in a single visit. Significant correlations (p # 0.05) existed between bilateral average AROM measures and bilateral average Y Balance Test scores at the ankle and hip. Specifically, ankle dorsiflexion AROM at 08 knee flexion significantly correlated with Anterior, Posterolateral, and Composite directional scores of the Y Balance Test (r = 0.497–0.736). Significant correlations in ankle dorsiflexion AROM at 908 knee flexion also existed with Anterior, Posterolateral, Posteromedial, and Composite directional scores (r = 0.472–0.795). Hip flexion AROM was significantly correlated with Posterolateral, Posteromedial, and Composite directional scores (r = 0.457–0.583). Significant correlations between asymmetries in AROM and asymmetries in the Y Balance Test existed only in ankle plantarflexion with Anterior, Posterolateral, and Composite directional scores of the Y Balance Test (r = 0.520–0.636). Results suggest that when used with recreationally active healthy adults, the Y Balance Test may help identify lowerextremity flexibility deficits and flexibility asymmetries in the ankle and hip regions but may need to be used in conjunction
Address correspondence to Raoul F. Reiser II, [email protected]. 29(5)/1240–1247 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
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with additional tests to understand a broader picture of functional movement and injury risk.
KEY WORDS Star Excursion Balance Test, bilateral asymmetry, active range of motion, injury risk, performance
INTRODUCTION
F
lexibility (also known as range of motion [ROM]) is typically considered a necessary component of sport and fitness (13). Lower-extremity flexibility, specifically, has been shown to be important for successful performance of sport movements (7) and activities of daily life (2,8). Beyond flexibility for function, flexibility is an essential factor for reducing injury risk (16,22). Side-toside symmetry in flexibility is also likely to be an important aspect of performance and injury prevention (1,3,6,14). The goniometer is arguably the most common and validated tool for measuring joint ROM (18). However, goniometry can be difficult to master and time consuming to complete on multiple joints and multiple axes within a joint. This makes comprehensive ROM assessment difficult when screening large groups of athletes. Furthermore, goniometers only measure ROM without simultaneously capturing other potential factors affecting injury or performance. Considering this, alternative screening methods could prove useful under many circumstances. One possible test that fits these criteria is the Star Excursion Balance Test (SEBT). The SEBT is a dynamic balance test requiring multiple reaches (also known as excursions) with 1 foot in a star-like pattern while maintaining balance on the stance leg. The Y Balance Test, or more simply the Y-Test, involving excursions in just 3 directions (anterior, posterolateral, and posteromedial) is becoming a commonly used more refined version of the traditional 8 excursion SEBT. The Y-Test is relatively inexpensive, portable, and easy to administer and does not require much specialized training but still shows good repeatability (see Ref. 9 for review). The 3 excursions of the Y-Test have been effectively used to screen for risk of injury or reinjury and injury risk related to asymmetry (see Ref. 9 for review). Furthermore, lowerextremity ROM has been shown to be a factor contributing
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Journal of Strength and Conditioning Research to larger excursion scores (11,21). The Y-Test may conceivably also measure the net effect of flexibility from 1 joint to the other, potentially serving as both an assessment of some types of active range of motion (AROM) and functional flexibility. Finally, the Y-Test has been effectively used to screen for lower-extremity asymmetry (20). Because flexibility is a potential element of asymmetry, the Y-Test may help assess side-to-side flexibility differences as well. Therefore, the Y-Test may serve as an alternative to less convenient and perhaps less comprehensive tests such as ROM measures using the goniometer. The goals of this investigation were to identify the correlations between bilateral flexibility in lower-extremity AROM measurements with bilateral performance in the YTest, in absolute terms (i.e., regardless of side-to-side asymmetry), and explore the relationship between lowerextremity asymmetries in AROM in comparison with asymmetries in Y-Test performance in a healthy young adult population. It was hypothesized that larger values of bilateral AROM would relate to larger excursion scores bilaterally on the Y-Test and higher levels of side-to-side asymmetry in AROM measures would relate to higher asymmetry in YTest scores. The results of this study will serve to develop a practical understanding of the relationships between flexibility and performance on the Y-Test in both absolute terms and flexibility relative to the contralateral limb, with the ultimate goal of improving screening methods for injury risk and performance.
METHODS Experimental Approach to the Problem
To accomplish the goals of this investigation, a cross-sectional research design was used. Healthy, active, pain-free subjects
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with limited previous injury were recruited. A population of healthy adults was used because it has previously been demonstrated that measurable asymmetry exists even in healthy people with no known reasons for being asymmetric (12,14,20). During a single visit lasting approximately 2 hours, subjects performed in order the Y-Test, a battery of 9 AROM measures, and 4 functional movements after adequate warmup and practice. The relationships between ground reaction force asymmetries during the functional movements (standing, bodyweight squats, countermovement jumps, and singleleg drop landings) and the Y-Test are presented elsewhere (19). Approximately half of the subjects returned for a second visit to repeat the measures. To test the proposed hypotheses, relationships between measures were assessed through correlations. Specifically, average bilateral AROM measurements were correlated to average bilateral Y-Test scores, and Y-Test excursion direction asymmetries were correlated to AROM asymmetries. Intraclass correlations were used to assess the repeatability of measures within those who returned for the repeat visit. Subjects
Twenty (9 men and 11 women) nonobese (body mass index ,30 kg$m22) healthy individuals aged 19–30 years (Table 1) participated after initial screening by a brief health and activity questionnaire. All subjects granted university’s Institutional Review Board–approved written informed consent after having the study explained to them. Subjects were identified as individuals who were currently recreationally active and were not specifically drawn from an athlete population. To meet inclusion criteria, recreational activities had to include jumping and squatting type movements. These movements were selected because of their high prevalence in exercise and sport along with their lower-extremity joint
TABLE 1. General subject characteristics.* Men (n = 9)
Age (y) Height (m) Mass (kg) BMI (kg$m22) Anatomical leg length NKL (cm) Anatomical leg length KL (cm) Anatomical LLD NKL-KL (cm) Absolute anatomical LLD (cm) Bilateral average leg length (cm) Functional LLD NKL-KL (cm) Absolute functional LLD NKL-KL (cm)
Women (n = 11)
Whole group (n = 20)
Mean
SD
Mean
SD
Mean
SD
a
22.3 1.8 74.6 23.5 97.2 96.2 1.0 1.3 96.7 0.2 0.4
1.4 0.1 4.8 1.7 3.5 3.8 1.2 0.8 3.6 0.5 0.3
21.6 1.7 61.2 22.4 88.2 87.4 0.8 0.9 87.8 20.1 0.1
3.4 0.1 5.3 2 3.7 3.8 1.0 0.8 3.7 0.2 0.2
21.9 1.71 67.2 22.9 92.2 91.4† 0.9 1.1 91.8 0.0 0.3
2.6 0.09 1.9 1.9 5.7 5.8 1.1 0.8 5.8 0.4 0.3
1.000 0.998 0.997 0.997 0.997 0.865 0.747 0.998 0.765 0.444
*a = Cronbach’s alpha for returning subjects; BMI = body mass index; NKL = non–kicking leg; KL = preferred kicking leg; LLD = leg length difference. †p , 0.01 between NKL and KL in whole group.
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Flexibility Asymmetries patterning relative to the Y-Test. Furthermore, to be considered recreationally active, subjects must have been involved in activities requiring these movement patterns at least once per week for the past 8 weeks based on self-report/recall. Recreational activities included, but were not limited to, resistance training, step aerobics, basketball, racquetball, baseball, and soccer. Although many recreational activities require a strong element of balance, no subjects were known to have prior exposure to the Y-Test or specific dynamic balance training, which might interfere with the validity of the testing protocol. Other exclusion criteria included self-reported pain, injury, or soreness to the lower back or lower extremities at the time of the visit. Any injuries must have healed with a return to regular activity at least 4 weeks before participation. Those with a history of back or lower-extremity pain, major previous surgery, bone, joint, or muscular disorder, history of neurological/orthopedic dysfunction, or pain that would limit the ability to perform functional tasks correctly were excluded. Any subjects with a known reason to perform these activities asymmetrically for anthropometric or orthopedic reasons were also excluded (e.g., known limb-length discrepancy, bilateral corrective devices, braces, anterior cruciate ligament tear/reconstruction, chronic ankle sprains, etc.). Pregnant women were also excluded.
Procedures
All subjects completed the initial visit to the laboratory, with 11 subjects returning a second time for the repeatability assessment (at least 2 days after the initial visit but no later than 31 days). Subjects were instructed to abstain from heavy exercise of the lower limbs and back for 48 hours before the visit and to limit exercise to normal daily activities for the lower extremities the day before and day of testing. Caffeine consumption was limited to normal daily intake, and no other ergogenic aids were allowed for consumption during the prior 24 hours leading up to the visit. It was confirmed before testing that subjects felt that they were under a normal physical and mental state without influence by a significant change in sleep, nutrition, or alcohol consumption the day of or the day preceding testing. Requirements and procedures of the second visit were identical to the initial visit. Retesting was performed at a similar time of day relative to the initial visit. After arriving and verifying eligibility, subjects were given orientation to the laboratory followed by measurement of body weight and height without shoes. Subjects wore clothing appropriate for physical activity (e.g., t-shirts and shorts). A warm-up of no less than 5 minutes on a stationary cycle ergometer was required for all subjects. Stretching was
TABLE 2. AROM measures performed (listed in order of execution top to bottom). Movement
Body position*
Hip flexion
Supine, straight knee
Hip extension
Prone, straight knee
Hip abduction
Fulcrum†
Proximal goniometer arm Midline of the upper body
Head of the fibula
Midline of the upper body
Head of the fibula
Contralateral ASIS
Inferior aspect of the ipsilateral patella Inferior aspect of the ipsilateral patella Center point midway between the 2 malleoli of the ankle Center point midway between the 2 malleoli of the ankle Lateral aspect of the fifth metatarsal Lateral aspect of the fifth metatarsal Lateral aspect of the fifth metatarsal
Supine, straight knee
Greater trochanter of the femur Greater trochanter of the femur Ipsilateral ASIS
Hip adduction
Supine, straight knee
Ipsilateral ASIS
Contralateral ASIS
Hip internal rotation
Seated, both knees bent at 908, lower legs hanging from measuring surface
Inferior aspect of the patella
Perpendicular to the floor
Hip external rotation
Seated, both knees bent at 908, lower legs hanging from measuring surface
Inferior aspect of the patella
Perpendicular to the floor
Ankle plantarflexion Ankle dorsiflexion 08 Ankle dorsiflexion 908
Supine, straight knee
Lateral malleolus Lateral malleolus Lateral malleolus
Head of the fibula
Supine, straight knee Supine, knee bent to 908
Distal goniometer arm
Head of the fibula Head of the fibula
*If not listed, body is assumed to be in neutral position. †Goniometer fulcrum was always aligned on the center of the landmark listed. ASIS = anterior-superior iliac spine.
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Journal of Strength and Conditioning Research not allowed at any point during the study to avoid confounding factors, which might be caused by stretching 1 side more vigorously than the other. After the warm-up, functional leg length asymmetry and anatomical leg length measurements were taken with the subject in the supine position on an elevated examination table as described by Hinson and Brown (10) and Evans (5), respectively. Briefly, functional leg length asymmetry is a measurement of the distance one limb protrudes relative to the other when lying relaxed, whereas anatomical leg length is a boney measure from the anterior-superior iliac spine to the medial malleolus. Functional and anatomical measurements were taken
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twice with the left side always measured first during the anatomical measurement, and the average of 2 measurements was used for analysis. The Y-Test was then performed in stocking feet as described by Plisky et al. (20) in the 3 common excursion directions: to the front (Ant), diagonally back and to the medial side of the reaching leg (PostMed), and diagonally back and to the lateral side of the reaching leg (PostLat). The distal aspect of the subject’s great toe was centered at the junction of the Y, which was outlined on the floor with secured inextensible tape measures (19). The subject performed a reach in all 3 directions on the left foot
TABLE 3. AROM descriptives (8).* Men (n = 9)
Hip flexion Bilateral Avg NKL-KL Abs NKL-KL Hip extension Bilateral Avg NKL-KL Abs NKL-KL Hip abduction Bilateral Avg NKL-KL Abs NKL-KL Hip adduction Bilateral Avg NKL-KL Abs NKL-KL Hip internal rotation Bilateral Avg NKL-KL Abs NKL-KL Hip external rotation Bilateral Avg NKL-KL Abs NKL-KL Ankle plantarflexion Bilateral Avg NKL-KL Abs NKL-KL Ankle dorsiflexion 08 Bilateral Avg NKL-KL Abs NKL-KL Ankle dorsiflexion 908 Bilateral Avg NKL-KL Abs NKL-KL
Women (n = 11)
Whole group (n = 20) a
Mean
SD
Mean
SD
Mean
SD
62 22 4
11 4 3
78 2 5
15 6 4
71 0 4
15 5 4
0.988 0.841 0.656
22 1 4
7 5 3
23 21 3
4 3 1
23 0 3
5 4 2
0.758 0.525 0.694
32 1 2
3 3 2
36 21 4
6 5 3
34 0 3
6 4 2
0.975 20.086 20.587
12 1 3
3 4 2
18 0 3
3 4 2
15 0 3
4 4 2
0.789 0.869 0.778
28 21 3
4 3 2
33 22 3
5 3 3
31 22† 3
5 3 2
0.953 0.905 0.795
28 2 4
4 4 3
31 2 3
5 3 2
30 2† 3
5 3 2
0.833 0.764 0.112
74 2 2
8 3 2
79 0 2
5 3 2
77 1 2
7 3 2
0.946 0.877 0.910
75 21 3
4 4 2
74 22 3
5 3 2
74 21 3
4 3 2
0.958 0.548 0.312
80 2 5
5 6 4
78 21 3
6 4 2
83 0 4
5 5 3
0.875 0.802 0.590
*a = Cronbach’s alpha for returning subjects; NKL = non–kicking leg; KL = kicking leg; Abs = absolute; AROM = active range of motion; Avg = average. †p # 0.05 between NKL and KL in whole group.
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Flexibility Asymmetries (Ant, PostMed, and then PostLat), followed by all 3 on the right foot. This was then repeated for a total of 6 correct practice trials. A correct trial required the heel of the plant foot to stay in contact with the ground, the hands remained on the hips at all times, the subject lightly brushed the measuring tape at the furthest point possible without planting weight onto the reaching foot, and the subject recovered to a single-leg standing position for at least 2 seconds. After the 6 practice trials, 3 more correct trials for which data were recorded completed in the same manner. The researcher visually identified the furthest point reached on the tape measure. A fourth or fifth trial was granted if excursion distance appeared to still be improving. The process of each AROM measurement was described to the subject and then performed as described by Norkin and White (18). However, unlike Norkin and White, measurements were conducted with the subject actively moving the joint in the specified direction, instead of being passively moved by the researcher (Table 2). The joint position was held for approximately 5–10 seconds while a measurement was taken with a universal goniometer (Model 01135; Lafayette Instrument Co. Inc., Lafayette, IN, USA). Each AROM measure was performed first on the left and then on the right side, before moving on to the next measure. After all 9 measures were performed, each was performed again for a second time, using the average of the 2 measurements in the analysis. All AROM measures were performed by the same researcher.
each excursion direction was also analyzed, as well as a summed Composite score of the maximums for each lower extremity. To control for the effect of limb length between subjects, Y-Test values were normalized to percent of average anatomical limb length (average of the right and left sides). The normalized preferred kicking leg (KL) Y-Test score (reaching with KL) was subtracted from that when performed with the non–kicking leg (NKL) to quantify the presence of asymmetry (%NKL 2 KL). Active range of motion asymmetry values were calculated by taking the NKL angular position and subtracting the KL angle (NKL8 2 KL8). Bilateral averages for Y-Test scores and AROM scores were also calculated. This was performed by averaging the scores on each side for all 3 YTest excursions, the Y-Test Composite scores, and all 9 AROM measures. Statistical Analyses
Group mean values and SD were compiled for all variables. To show the overall magnitude of asymmetries, mean and SD of absolute levels of asymmetries were compiled along with the side-to-side (NKL-KL) difference. Paired t-tests were performed on all NKL vs. KL values to determine the existence of significant population-wide bilateral differences related to KL. Pearson’s correlations (r) were performed comparing bilateral average and asymmetry values in each AROM measure with each individual and combination of excursions in the Y-Test, as well as anatomical leg length differences. Intraclass correlations (Cronbach’s Alpha, a) were used to establish intersession repeatability of all measures reported. Finally, a or r , 0.500 were classified as weak, from 0.500 to 0.799 were classified as moderate, and $0.800 were classified as strong. Statistical analysis was conducted in IBM SPSS
Data Processing and Analyses
The Y-Test was analyzed using the average (Avg) of the last 3 trials for each reach direction for each lower extremity and the average of the total of the 3 reach directions (also known as Composite). The maximum (Max) value measured for
TABLE 4. Bilateral Avg AROM vs. Y-Test correlations (r) (n = 20).* Ant
PostLat
PostMed
Composite
Bilateral Avg
Avg
Max
Avg
Max
Avg
Max
Avg
Max
Hip Flex Hip Ext Hip Abd Hip Add Hip IR Hip ER Ankle PF Ankle DF 08 Ankle DF 908
0.411 0.037 0.347 0.264 0.124 0.124 20.211 0.736z 0.795†
0.347 0.012 0.301 0.234 0.076 0.065 20.230 0.706z 0.777z
0.457† 0.047 0.081 0.210 0.121 0.039 20.288 0.497† 0.650z
0.402 0.039 20.019 0.106 0.053 0.084 20.314 0.408 0.560†
0.583z 0.256 0.261 0.142 0.319 0.129 0.175 0.301 0.424
0.510† 0.275 0.182 0.079 0.293 0.148 0.118 0.320 0.472†
0.516† 0.106 0.211 0.191 0.219 0.120 20.102 0.540† 0.667z
0.490† 0.150 0.170 0.136 0.183 0.142 20.142 0.517† 0.665z
*AROM = active range of motion; Ant = anterior; PostLat = posterolateral; PostMed = posteromedial; Avg = average; Max = maximum; Flex = flexion; Ext = extension; Abd = abduction; Add = adduction; IR = internal rotation; ER = external rotation; PF = plantarflexion; DF = dorsiflexion. †p # 0.05 zp , 0.01
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TABLE 5. AROM asymmetries vs. Y-Test asymmetries correlations (r) (n = 20).* Ant
Hip Flex Hip Ext Hip Abd Hip Add Hip IR Hip ER Ankle PF Ankle DF 08 Ankle DF 908
PostLat
PostMed
Composite
Avg
Max
Avg
Max
Avg
Max
Avg
Max
0.238 0.097 20.049 20.067 0.149 0.032 0.565† 20.162 20.423
0.165 0.108 20.108 0.059 0.103 0.089 0.636z 20.192 20.288
0.041 0.156 0.001 0.121 20.142 20.086 0.520† 20.106 20.021
20.022 0.080 20.133 0.047 20.194 20.152 0.352 20.015 20.170
20.109 20.227 20.325 0.099 20.099 20.040 0.290 0.243 20.264
20.140 20.254 20.182 0.094 20.009 20.094 0.279 0.237 20.309
0.014 20.024 20.183 0.078 20.058 20.050 0.565z 0.043 20.297
0.015 20.026 20.144 0.094 0.053 20.049 0.439 0.108 20.391
*AROM = active range of motion; Avg = average; Max = maximum; Ant = anterior; PostLat = posterolateral; PostMed = posteromedial; Flex = flexion; Ext = extension; Abd = abduction; Add = adduction; IR = internal rotation; ER = external rotation; PF = plantarflexion; DF = dorsiflexion. †p # 0.05 zp , 0.01.
Statistics version 19.0 (Chicago, IL, USA) with significance set at p # 0.05.
RESULTS Eighteen of the 20 subjects indicated that the right leg was their KL and 2 indicated the left leg. General subject characteristics tended to be highly repeatable from day to day for the 11 subjects (6 women and 5 men) who returned for a second visit, except for absolute functional leg length difference (Table 1). Repeat visits averaged 19.0 6 9.5 days after the initial visit. Although small in magnitude, the anatomical leg length of the NKL was on average significantly longer than the KL. Small absolute levels of asymmetry, within 628 NKL-KL, existed in the AROM measures, although only hip internal and external rotations were statistically significant between limbs (Table 3). Active range of motion asymmetries typically exhibited moderate-to-strong repeatability, although hip external rotation and ankle dorsiflexion at 08 knee flexion both had poor repeatability in absolute measures, whereas hip abduction was the opposite with moderate repeatability in absolute measures and poor repeatability in relative measures (Table 3). Anatomical leg length difference did not significantly correlate with any of the AROM asymmetries. Y-Test results are detailed in the study by Overmoyer and Reiser (19). In brief, small absolute levels of bilateral differences in Y-Test scores existed, but none of the NKL vs. KL comparisons were statistically significant. Furthermore, individual leg and bilateral differences in Y-Test scores typically showed good repeatability, although absolute bilateral differences tended to be less repeatable than relative differences. The bilateral average AROM scores and bilateral average Y-Test scores had several significant correlations existing
between them (Table 4). The significant correlations in this comparison were weak to moderate but never strong. Significant findings included weak-to-moderate correlations in hip flexion AROM measures with Avg and Max PostMed, Avg and Max Composite scores, and Avg PostLat scores (r = 0.457–0.583). Significant weak-to-moderate correlations also existed in ankle dorsiflexion at 908 knee flexion with the Avg and Max Anterior, Avg and Max Posterolateral, Max PostMed, and Avg and Max Composite scores (r = 0.472– 0.795). Additionally, significant moderate correlations between ankle dorsiflexion at 08 knee flexion and both Avg and Max Anterior and Composite scores existed (r = 0.517– 0.736), while also showing a nearly moderate correlation when comparing ankle dorsiflexion at 08 knee flexion with Avg PostLat (r = 0.497). When comparing AROM asymmetries with Y-Test asymmetries, there were significant moderate correlations, but exclusively in ankle plantarflexion AROM (Table 5). This included ankle plantarflexion with Avg Ant, Max Ant, Avg PostLat, and Avg Composite (r = 0.565, 0.636, 0.520, and 0.565, respectively). Finally, anatomical asymmetries did not significantly correlate with Y-Test asymmetries except for a weak but significant inverse correlation with asymmetries in the Avg PostLat excursion (r = 20.459).
DISCUSSION Overall, our Y-Test scores were highly comparable with other studies as previously discussed in the study by Overmoyer and Reiser (19) with Y-Test asymmetries demonstrating good day-to-day repeatability as was expected (17,20). Bilateral averages for AROM measures were within expected ranges of healthy active adults (14,18). Small levels of asymmetries existed within this population during AROM VOLUME 29 | NUMBER 5 | MAY 2015 |
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Flexibility Asymmetries measurements, which is consistent with other studies (4,14) and when performing the Y-Test (20). The expression of AROM also showed good repeatability from day-to-day in most cases as expected (18). However, although AROM asymmetries were frequently highly repeatable, they exhibited low repeatability in some measures of some individuals. This day-to-day variability does not preclude the possibility that on any given day, AROM asymmetries could still be a risk factor or associated with other measures. Furthermore, the observed small differences in anatomical leg length do not appear to play an important role in any of the observed asymmetries. Therefore, the results are appropriate for addressing the proposed goals, which sought to explore how bilateral average AROM measures in these joint motions related to bilateral average Y-Test excursions and the relationships between asymmetries within lower extremity AROM and asymmetries in Y-Test performance in a healthy active population. The results when looking at relationships among AROM and the Y-Test relative to bilateral averages (i.e., not looking at side-to-side asymmetry) partially support our hypothesis. Dorsiflexion at both 08 and 908 knee flexion seem to be the most important factors when looking at flexibility’s role in YTest performance, especially in regard to the Ant excursions. This is likely emphasized in the Y-Test protocol used here where the heel was required to remain in contact with the floor, thus noticeably applying a stretch to the calf muscles during the Ant excursion. However, the PostLat direction also seemed to moderately rely on the dorsiflexion at 908 knee flexion ROM, which is not as easily explained with the heel on the ground protocol. Additionally, bilateral average hip flexion showed a moderate relationship with the PostMed excursion, which may point to this joint motion, playing an important role in performance during this excursion. The Composite Y-Test scores also showed significant correlations to these variables, but the correlations were not any stronger than the strongest of its constituent parts, meaning that these composite measures likely have less worth than looking at individual measures alone. Plisky et al. (20) reported that female high-school basketball players who had Composite reach distances under a certain threshold were 6.5 times more likely to have lower extremity injury over the course of the upcoming season. Although the population they used consisted of a younger and potentially more athletic group, it is possible, based on these data, that appropriate AROM in dorsiflexion and hip flexion may be a contributor to this higher injury rate. Because of only moderate correlations, this alone is unlikely to explain the majority of their findings, however. Furthermore, it has been suggested that tightness in the soleus and gastrocnemius, which would be stretched during dorsiflexion, may cause increased knee valgus (15), again relating to a higher level of injury risk (23). Therefore, it is possible that the Y-Test is picking up on this potential compensation, which may ultimately contribute to lower extremity injury.
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The results regarding asymmetries in AROM relative to asymmetries in Y-Test scores again partially support our hypothesis. Ankle plantarflexion seemed to be by far the biggest contributor to asymmetry in the Y-Test of all the AROM measures conducted. Plantarflexion asymmetry appears to contribute to Ant, PostLat, and Composite asymmetries. This suggests that the ability to point your toe may be a strong factor in asymmetry in excursion scores. This might be somewhat telling to the results of Plisky et al. (20) as well. Plisky et al. found that an Ant excursion asymmetry of more than 4 cm gave high-school basketball players a 2.5-fold increase in lower extremity injury risk. Our findings might suggest that asymmetry in plantarflexion has a role in this increased injury risk, although it is unclear how. Interestingly, plantarflexion did not play a role in bilateral Y-Test scores, having a weak and statistically insignificant relationship with all excursions (│r│ # 0.314). This might be because asymmetry scores tend to be small in magnitude compared with the overall Y-Test scores. Thus, a few degrees difference in plantarflexion asymmetry might have a significant effect on asymmetry scores but have an insignificant effect on overall Y-Test performance. Some limitations exist within the research design of this study. It is unknown whether being above or below a baseline threshold of flexibility or asymmetry might have a greater effect or if there is a threshold level of AROM that may relate to a more pronounced contribution to Y-Test scores. Within this study, this threshold, if it exists, could not be illuminated. Furthermore, the population examined here was overall active, young, and injury-free and therefore was unlikely to have very low levels of flexibility or high levels of asymmetry. Although it gives insight into a more fit and active population, this might contribute to a lower level of correlation in some cases than a population that has more reason to be asymmetric. With a more asymmetric subject pool, these correlations could have much more strength, but this is currently unknown. Additionally, no sex-specific analyses were performed. Although the majority of the literature does not support the need for this, there may be some rational for doing so in the Y-Test (see Ref. 9 for review). Because of this possibility, this is a subject requiring further research.
PRACTICAL APPLICATIONS In a young healthy population with no specific reasons to be highly asymmetric, the Y-Test data suggest that using the YTest as a screening method may be useful in exposing some lower-extremity flexibility asymmetries or bilateral deficits in flexibility. Of all the joint measures examined, ankle dorsiflexion and hip flexion are the primary AROM measures, which seem to contribute to the overall Y-Test scores. This seems consistent with the study by Robinson and Gribble (21) and Hoch et al. (11), which have previously suggested that these joint motions play an important role in SEBT or Y-Test performance. Additionally, side-to-side differences in
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Journal of Strength and Conditioning Research Y-Test scores may indicate asymmetries in ankle plantarflexion. However, Y-Test asymmetries seem unlikely to expose asymmetries in most lower extremity AROM measures and may therefore not be a good replacement for goniometer measures in many cases. Regardless, the Y-Test alone may be very good at exposing some flexibility asymmetries, although at this time, it appears unlikely to be able to capture the wide range that a battery of goniometer measures can. How groups/individuals with higher levels of asymmetries and specific differences between men and women need further exploration.
ACKNOWLEDGMENTS The authors would like to express their gratitude to the participants, as well as Hung Mai, Katelyn Walker, Kent Gneiting, and Katherine Brown, who freely volunteered their time toward this unfunded research project. The authors have no conflict of interest to declare nor do the results of this study constitute endorsement of any products by the authors or the National Strength and Conditioning Association.
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