MEASUREMENT IN PHYSICAL EDUCATION AND EXERCISE SCIENCE, 7(2), 89–100
Copyright © 2003, Lawrence Erlbaum Associates, Inc.
Considerations for Normalizing
Measures of the Star Excursion Balance
Test
Phillip A. Gribble and Jay Hertel
Department of Kinesiology
Athletic Training Research Lab
Pennsylvania State University
This study was designed to examine the role of foot type, height, leg length, and
range of motion (ROM) measurements on excursion distances while performing the
Star Excursion Balance Test (SEBT), a test of dynamic postural control. Participants
(n = 30) performed 3 trials of the SEBT in each of the 8 directions while balancing on
the right and left legs. No statistically significant relations were found between foot
type or ROM measurements and excursion distances with the SEBT. Significant correlations were revealed between height and excursion distance and leg length and excursion distance with leg length having the stronger correlation. Using raw excursion
measures, males were found to have significantly greater excursion distances than females; however, after normalizing excursion distances to leg length, there were no
significant differences related to gender. In conclusion, when using the SEBT for experimental or clinical purposes, participants’ excursion distances should be normalized to leg length to allow for a more accurate comparison of performance among
participants.
Key words: postural control, foot type, dynamic balance
Measurement of postural control is an important tool in the assessment of pediatric, geriatric, and athletic populations for establishing levels of neuromuscular
function for the purposes of injury prevention and rehabilitation. Postural control
is often described as being either static (attempting to maintain a position with
Requests for reprints should be sent to Phillip Gribble, Penn State University, 266 Recreation
Building, University Park, PA 16802. E-mail: gribblepa@hotmail.com
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minimal movement) or dynamic (maintaining a stable base of support while completing a prescribed movement; Winter, Patla, & Frank, 1990).
Static postural control is commonly quantified through instrumented measurements of ground reaction forces or less sophisticated non-instrumented means. A
clinician or researcher may assess static postural control by having an individual
attempt to maintain a stationary position while standing on either one or both feet.
Ground reaction forces may be measured by having a participant balance on a
force plate. Postural control is then typically quantified through various measures
of velocity, area, or variability of the ground reaction forces or a related variable
(Guskiewicz & Perrin, 1996). Non-instrumented measures include variables such
as time that a participant can maintain the prescribed stance (Freeman, Dean, &
Hanham, 1965) or subjective error scoring systems (Riemann, Caggiano, &
Lephart, 1999). A common clinical example of static postural control assessment
is the modified Rhomberg test, first described by Freeman (Freeman et al., 1965).
This test is performed by having participants stand as motionless as possible, on
one foot, as a series of task demands are added to challenge the postural control
system. These task demands include closing the eyes, tilting the head up, and
touching an index finger to the nose. Although this test is commonly used in the assessment of cerebral concussion (bilateral stance) and lower extremity joint injuries (unilateral stance), it typically does not place strength or movement demands
on the participant.
Dynamic postural control often involves completion of a functional task without compromising one’s base of support. The advantage of assessing dynamic postural control is that additional demands of proprioception, range of motion (ROM),
and strength are required along with the ability to remain upright and steady. Numerous tests have been developed to assess dynamic postural control in the pediatric (Donahoe, Turner, & Worrell, 1994) and geriatric (Berg et al., 1990;
Rossiter-Fornoff, Wolf, Wolfson, & Buchner, 1995; Tinetti 1986) populations, but
very few tests that truly stress the dynamic balance capabilities of the healthy, athletic population. The Star Excursion Balance Test (SEBT) is one such test that provides a significant challenge to an athlete’s postural control system (Earl & Hertel,
2001; Gray, 1995; Hertel, Miller, & Denegar, 2000; Kinzey & Armstrong, 1998;
Miller, 2001; Olmsted, Carcia, Hertel, & Shultz, 2002).
The SEBT involves having a participant maintain a base of support with one leg
while maximally reaching in different directions with the opposite leg, without
compromising the base of support of the stance leg. Strong intra-rater reliability of
measurements with the SEBT has been demonstrated by Kinzey and Armstrong
(1998) [ICC (2,1): 0.67–0.87)] and Hertel et al. (2000) [ICC (2,1): 0.81–0.96]. The
SEBT has shown sensitivity in screening for functional deficits related to
musculoskeletal injuries (Earl, 2002; Miller, 2001; Olmsted et al., 2002). In addition, Earl and Hertel (2001) demonstrated the usefulness of the SEBT for the re-
NORMALIZATION CONSIDERATIONS OF THE SEBT
91
cruitment of lower extremity musculature contraction and discussed its application
in rehabilitating various lower extremity musculoskeletal injuries.
Researchers have provided evidence that the SEBT is sensitive for screening
musculoskeletal impairments, such as chronic ankle instability (Olmsted et al.,
2002), quadriceps strength deficits (Miller, 2001), and patellofemoral pain syndrome (Earl, 2002). Olmsted et al. reported decreased reaching distances during
performance of the SEBT in patients with chronic ankle instability compared to
matched-healthy control participants.
Miller (2001) correlated quadriceps strength deficits with performance of the
SEBT among subjects who had undergone anterior cruciate ligament reconstruction (ACLR). The ACLR subjects who demonstrated a quadriceps strength deficit
during isokinetic testing also demonstrated decreased anterior reaching distance
while performing the SEBT compared to uninjured matched control subjects.
Earl (2002) found that when assessing function among patients with
patellofemoral pain (PFP), the patients with PFP had significantly reduced performance on the SEBT compared to matched controls (Earl, 2002). Following 6
weeks of structured rehabilitation, the PFP subjects had improved their SEBT performance such that there no longer existed a deficit between the PFP and control
groups.
Various predictors of static postural control measures, such as muscle strength,
architectural foot type, and mental status, have been studied (Hertel, Gay, &
Denegar, 2002; Topp, Estes, Dayhoff, & Suhrheinrich, 1997). The SEBT has been
shown to be a reliable and valid instrument for assessing dynamic postural control
(Gray, 1995; Hertel et al., 2000; Kinzey & Armstrong, 1998; Olmsted et al., 2002);
however, predictive factors for performance of the SEBT have not been examined.
This study was designed to examine the role of gender, foot type, height, leg
length, and lower extremity ROM measurements on dynamic postural control as
assessed through the SEBT and to determine the need for normalization of performance data.
METHODS
Participants
Thirty (12 men, 18 women) recreationally active participants volunteered for this
study. Descriptive data of the participants is presented in Table 1. All participants self-reported that they were free of vestibular disorders, cerebral concussions, and lower extremity injuries during the previous 6 months. The study was
approved by the university’s institutional review board, and each participant read
and signed an approved informed consent form, in concordance with the university’s Institutional Review Board.
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TABLE 1
Means and Standard Deviations Summary Statistics for Participants
Gender
Male
(n = 12)
Female
(n = 18)
Note.
Mass (kg)
Leg
Length
(cm)
Hip ER
(degrees)
Hip IR
(degrees)
Ankle DF
(degrees)
69.2 ± 2.1
79.2 ± 11.5
89.9 ± 4.3
41.2 ± 9.2º
34.4 ± 8.4º
27.0 ± 3.0º
66.4 ± 3.2
62.0 ± 8.8
87.4 ± 5.0
43.1 ± 11.1º
43.2 ± 10.1º
27.2 ± 5.2º
Age
(Years)
Height (cm)
23.2 ± 3.8
22.4 ± 1.4
DF = dorsiflexion; ER = external rotation; IR= internal rotation.
Measurements of Predictive Factors
Foot type, leg length, hip internal and external ROM, and ankle dorsiflexion were
measured bilaterally in all participants by the same investigator. Participants’ feet
were classified into one of three foot-type categories according to the procedures
described by Root, Orien, and Weed (1971) resulting in 22 pes planus, 26 pes
rectus, and 12 pes cavus feet.
Height was measured with a standard height chart. Leg length was measured on
each limb with participants lying supine. A tape measure was used to quantify the
distance from the anterior superior iliac spine to the center of the ipsilateral medial
malleolus. Hip internal and external rotation was measured with a standard
goniometer with the participants lying prone. Dorsiflexion at the ankle was also
measured with a standard goniometer with the participants standing with one foot
in front of the other while leaning forward until the heel of the posterior foot began
to lift off the ground (Denegar, Hertel, & Fonseca, 2002).
SEBT Procedures
The SEBT was performed with the participants standing in the middle of a grid
formed by eight lines extending out at 45° from each other (see Figure 1). The participant was asked to reach as far as possible along each of the eight lines, make a
light touch on the line, and return the reaching leg back to the center, while maintaining a single-leg stance with the other leg in the center of the grid (see Figure 2).
Participants were instructed to make a light touch on the ground with the most distal part of the reaching leg and return to a double-leg stance without allowing the
contact to affect overall balance. The terminology of excursion directions is based
on the direction of reach in relation to the stance leg (see Figure 1). When reaching
in the lateral and posterolateral directions, participants must reach behind the
stance leg to complete the task.
Participants were allowed to practice reaching in each of the eight directions six
times to minimize the learning effect (Hertel et al., 2000). Following a 5-min rest
NORMALIZATION CONSIDERATIONS OF THE SEBT
FIGURE 1
93
Reaching directions for the Star Excursion Balance Test.
FIGURE 2 Performance of the Star Excursion Balance Test with a left stance leg reaching
into the posteromedial direction.
period, participants performed three trials in each of the eight directions. They began with the anterior direction and progressed clockwise around the grid. All participants began with a right stance leg in the center of the grid. After completion of
the three trials in the eight directions and another 5-min rest period, the test continued with a left stance leg.
The investigator recorded each reach distance with a mark on the tape as the distance from the center of the grid to point of maximum excursion by the reach leg.
At the conclusion of all trials, the investigator measured the distances of each excursion with a standard tape measure. If the investigator felt the participant used
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the reaching leg for a substantial amount of support at any time, removed his or her
foot from the center of the grid, or was unable to maintain balance on the support
leg throughout the trial, the trial would be discarded and repeated.
Statistical Analysis
Dependent t tests were performed to compare each of the eight excursion distances
of the right and left limbs of participants. Because no significant differences (p >
.05) were identified, data from the right and left limb trials were averaged. A series
of eight independent t tests was used to examine the differences in normalized excursion distances in the eight directions as a function of gender. Eight separate
analysis of variance (ANOVA), with one between-groups factor (foot type), were
computed; one for each excursion direction. Pearson product–moment correlations were calculated to explore the bivariate relations between excursion distance
and height, leg length, hip internal ROM, hip external rotation ROM, and ankle
dorsiflexion ROM.
Leg length and height were both found to be significantly correlated, to reach
distance in the majority of the directions (see Table 2), thus the Pearson product–moment correlation between height and leg length was calculated (r = .89).
Because leg length was found to be the most highly correlated factor, and leg
length and height were highly correlated, excursion distances were normalized to
the participant’s leg length for further analysis. Normalization was performed by
dividing each excursion distance by a participant’s leg length, and then by multiplying by 100. Normalized values can thus be viewed as a percentage of excursions
distance in relation to a participant’s leg length.
Eight separate ANOVAs with one between-groups factor (foot type) were then
computed on the normalized excursion distances. In addition, a series of eight independent samples t tests were utilized to examine the differences in normalized
TABLE 2
Relationship Between Height and Excursion and Leg Length and
Excursion (R2 Values)
Reaching Direction
Height
Leg Length
Ant
Antlat
Lat
Postlat
Post
Postmed
Med
Antmed
0.19***
0.11*
0.01
0.04
0.10*
0.13**
0.14**
0.18***
0.23***
0.18**
0.02
0.04
0.10*
0.14**
0.11**
0.19***
*p < .05. **p < .01. ***p < .001.
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NORMALIZATION CONSIDERATIONS OF THE SEBT
excursion distances as a function of gender. The experiment wise alpha level was
set at p < .05. For the series of t tests (limb, gender) and ANOVAs (foot type),
Bonferroni corrections were utilized, resulting in an adjusted significance level of
p < .006 (see note in Table 3).
RESULTS
The dependent t tests revealed no significant differences between the right and left
limb excursion distances; therefore, data for both limbs were combined for subsequent analyses. Height, leg length, and ROM measurements are presented in Table
1. A significant correlation (p < .05) was found between height and excursion distance, and leg length and excursion (p < .05) distance in six of the eight directions:
anterior, anteromedial, medial, posteromedial, posterior, and anterolateral. For the
significant correlations, r2 values ranged from .10 to .19 between height and excursion distances, and from .10 to .23 between leg length and excursion distances (Table 2). Stronger correlations were found between leg length and excursion distances than between height and excursion distances. Height and leg length were
found to strongly correlate to each other (r2 = .77, p < .05). No significant correlations were found between internal rotation of the hip, external rotation of the hip,
or dorsiflexion of the ankle and excursion distances (p > .05).
Men were found to have significantly (p < .006) greater raw excursion distances
than women in three of the eight reaching directions (posterior, posteriomedial,
TABLE 3
Differences in Normalized Excursion Distances for Men and Women
Raw Scores (cm)*
Reaching
Directions
ANT
ALAT
LAT
PLAT
POST
PMED
MED
AMED
Normalized (% of leg length)
Male
Female
p
Male
Female
p
71.2 ± 7.4
66.4 ± 8.0
71.9 ± 15.5
81.2 ± 11.9
84.4 ± 9.6
86.0 ± 8.1
87.8 ± 8.5
76.7 ± 7.7
67.1 ± 5.4
65.1 ± 6.5
69.6 ± 12.0
74.6 ± 11.5
74.4 ± 11.4
77.7 ± 10.1
79.1 ± 9.2
72.5 ± 6.4
.014
.493
.508
.035
.001*
.001*
<.0005*
.026
79.2 ± 7.0
73.8 ± 7.7
80.0 ± 17.5
90.4 ± 13.5
93.9 ± 10.5
95.6 ± 8.3
97.7 ± 9.5
85.2 ± 7.5
76.9 ± 6.2
74.7 ± 7.0
79.8 ± 13.7
85.5 ± 13.2
85.3 ± 12.9
89.1 ± 11.5
90.7 ± 10.7
83.1 ± 7.3
.192
.657
.962
.176
.009
.020
.012
.277
Note. Means of three trials and standard deviation values in each reaching direction. Scores adhere to a Bonferroni correction level of significance of p < .006 (.05 divided by number of reaching directions, 8).
*p < .006.
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medial); however, following normalization no significant differences (p > .006)
between genders were identified. These results are listed in Table 3.
No significant differences between foot types were found in any of the eight directions for raw excursion distances or normalized excursion distances (p > .05).
These results are illustrated in Figures 3 and 4.
FIGURE 3 Raw excursion distances for the eight directions by foot type. ALAT =
anterolateral; AMED = anteromedial; ANT = anterior; LAT = lateral; MED = medial; PLAT =
posterolateral; POST = posterior; PMED = posteromedial.
FIGURE 4
Normalized excursion distances for the eight directions by foot type.
NORMALIZATION CONSIDERATIONS OF THE SEBT
97
DISCUSSION
Our results demonstrate that height and leg length were positively related to performance on the SEBT. The importance of normalizing excursion distance data
(by factoring out leg length) was illustrated by the existence of significant differences in excursion distances between genders on raw excursions distance scores;
however, a lack of gender differences was found following normalization of excursion distances to leg length. When using the SEBT as an assessment tool, considerations for normalization should include leg length. This includes either normalizing excursion data to leg length or matching paired participants for leg length. No
significant relations were identified between foot type, hip rotation ROM, or ankle
dorsiflexion ROM and excursion distances.
To contribute to the body of knowledge of the SEBT, we attempted to examine
several factors that could influence postural control among healthy, physically active individuals. The SEBT is designed to challenge posture during multiple reaching tasks; and the reliability (Hertel et al., 2000; Kinzey & Armstrong, 1998) as
well as sensitivity (Earl, 2002; Miller, 2001; Olmsted et al., 2002) has been previously established. No previous researchers have attempted to examine factors that
may potentially contribute to performance. While our results do establish correlations between leg length, height, and reach distance, the correlation values are low,
establishing the need for further investigation into performance contributions during the SEBT.
The SEBT involves maximizing lower extremity reach distance with one limb
while maintaining balance on the contralateral limb. Logically leg length would
correlate significantly with excursion distance, as a longer limb would give a participant an advantage in reaching that limb further. In addition, because height and
leg length strongly correlate with each other, it is inherent that height and excursion distance would also correlate significantly. While the correlations for height
and leg length to excursion distance were significant, they were not especially
strong. The highest correlations occurred between leg length and excursion distance in the three anterior directions (anterior, anterolateral, anteromedial), with an
r2 value of just .23. This indicates that while leg length is a significant predictor of
performance on the SEBT, other factors not assessed for in this study account for
the majority of the variance associated with excursion distance.
In a recent study by Hertel et al. (2002), the relation between foot type and static
postural control was examined. Participants with cavus feet demonstrated significantly greater center of pressure area measures compared to rectus feet. The results
of our study show that foot type was not similarly related to dynamic postural control as assessed with the SEBT. During static measurements of postural control, the
body remains relatively fixed over the base of support. Hertel et al. (2002) speculated that the reason for impaired postural control in participants with cavus feet
was related to a smaller amount of contact of the plantar surface of the foot with the
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ground. The lack of an anatomical block through contact allows the base of support
in a pes cavus foot to shift medially and laterally. In addition, perhaps a lack of contact surface limited the amount of cutaneous feedback, which would decrease
compensatory actions leading to increased postural sway.
In a static task of postural control, the goal is to minimize displacement of the
center of pressure, a derivative of the vertical ground reaction force. In the measure
of dynamic postural control used in this study, the goal is to maximize reach distance while maintaining unilateral support. Hertel et al. (2002) demonstrated that
center of pressure excursion could be affected by the amount of ground contact related to foot type. Postural sway is not quantified in the SEBT, but it is inherent to
the test that some shifting of the center of pressure will occur to maximize excursion distance. Foot type, however, did not significantly affect the performance of
the SEBT, possibly due to other compensatory motions or reaching strategies, or
both, that allow a subject to overcome a deficit potentially due to foot type.
No relation was found between ROM measurements at the hip and ankle and
performance on the SEBT. We allowed participants ample practice of the SEBT,
but we did not dictate their strategy for achieving maximum reaching distance beyond what was described. Thus, an individual could incorporate a variety of movement patterns for positioning of the trunk as well as the joints of the upper and
lower extremities. Variations in ROM at the hip and ankle among individuals did
not affect overall dynamic balance performance with the SEBT. Because we did
not require a specific pattern of movement to achieve maximum performance, an
individual conceivably could overcome a deficit in range of motion at one joint by
using more ROM at another joint to achieve the specified goal. Further research is
warranted to explore movement patterns associated with performance of the
SEBT.
Another possible predictor of performance that was not investigated in this
study was strength. The SEBT requires neuromuscular control though proper joint
positioning as well as strength in surrounding musculature to create and maintain
the necessary positions throughout the test. Future researchers should investigate
the relation of muscle strength and fatigue of various lower extremity muscle
groups and performance on the SEBT. Other physical factors that were not examined in this study that may be associated with variations in performance include the
following: strength, neuromuscular control, and ROM at additional joints. By
identifying arthropometric predictors of SEBT performance (height, leg length)
and normalizing to these measures, perhaps a more accurate assessment of postural control would be available.
A potential limitation in our study is that the order of trials was not counterbalanced. The order of testing followed a dominant, non-dominant stance leg order,
always in the clockwise direction. Future researchers should include a randomized
order of testing to avoid potential confounding factors such as learning effect and
fatigue.
NORMALIZATION CONSIDERATIONS OF THE SEBT
99
The SEBT is a promising test of postural control that may be useful in assessing
functional deficits in those with lower-extremity orthopedic injuries. The results of
this study suggest that among young, physically active individuals, leg length of
the participants must be considered in normalizing performance data. We recommend that when using the SEBT for experimental purposes, investigators should
either normalize excursion distances to participant leg length or use control participants who are matched to experimental participants according to leg length.
ACKNOWLEDGMENT
We thank Anthony Piegaro, ATC, for his assistance in data collection during this
project.
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