MILITARY MEDICINE, 178, 11:1264, 2013

Y-Balance Test: A Reliability Study Involving Multiple Raters

LTC Scott W. Shaffer, SP USA*; LTC Deydre S. Teyhen, SP USA†; CPT Chelsea L. Lorenson, SP USA*;
CPT Rick L. Warren, SP USA*; CPT Christina M. Koreerat, SP USA*; CPT Crystal A. Straseske, SP USA*;
Lt Col John D. Childs, USAF BSC*

ABSTRACT The Y-balance test (YBT) is one of the few field expedient tests that have shown predictive validity
for injury risk in an athletic population. However, analysis of the YBT in a heterogeneous population of active adults
(e.g., military, specific occupations) involving multiple raters with limited experience in a mass screening setting is

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lacking. The primary purpose of this study was to determine interrater test–retest reliability of the YBT in a military
setting using multiple raters. Sixty-four service members (53 males, 11 females) actively conducting military training
volunteered to participate. Interrater test–retest reliability of the maximal reach had intraclass correlation coefficients
(2,1) of 0.80 to 0.85 with a standard error of measurement ranging from 3.1 to 4.2 cm for the 3 reach directions (anterior,
posteromedial, and posterolateral). Interrater test–retest reliability of the average reach of 3 trails had an intraclass
correlation coefficients (2,3) range of 0.85 to 0.93 with an associated standard error of measurement ranging from 2.0 to
3.5cm. The YBT showed good interrater test–retest reliability with an acceptable level of measurement error among
multiple raters screening active duty service members. In addition, 31.3% (n = 20 of 64) of participants exhibited an
anterior reach asymmetry of >4cm, suggesting impaired balance symmetry and potentially increased risk for injury.

INTRODUCTION associated with reduced injuries,18,19 and increased neuro-

Traumatic and overuse lower extremity injuries are common muscular power and motor control during vertical jumps and
and unfortunately injury prediction is complex and multifac- single-legged drop landings.20–23 Screening balance impair-
torial.1–5 More than 10,000 Americans seek medical treat- ments seems warranted based on its potential to predict and
ment for sports-, recreational-, and exercise-related injuries prevent musculoskeletal conditions of the lower extremity.
on a daily basis.6 Researchers have estimated that 50% to Unfortunately, time-efficient, field-expedient, and reliable mea-
80% of injuries are overuse in nature and involve the lower sures of balance with exhibited discriminant and predictive
extremity.1,5,7 Overuse lower extremity injuries have a specific validity for lower extremity injury are limited.10
impact on U.S. military readiness, accounting for an estimated The Star Excursion Balance Test (SEBT) requires mini-
3.8 million injury-related limited duty days in 2004.8 The mal equipment and can be implemented in “multiple settings
impact of lower extremity injuries in the military emphasizes and diverse populations (e.g., athletic preseason screening,
the need for efficient and effective neuromusculoskeletal occupational participation screening, and military physical
screening. Unfortunately, reliable and field-expedient injury training sessions).” The SEBT measures the ability to main-
screening tools used to screen large populations (athletes, tain single-leg stance on one leg while the contralateral leg
military, and occupation specialties) in an efficient manner reaches as far as possible in 8 directions. The SEBT has
with multiple examiners are limited.9 exhibited discriminant validity for identifying individuals
Impaired balance is one of the several risk factors that with chronic ankle14,24–26 and ACL instability.17 In particular,
have been associated with increased risk of lower extremity Hubbard et al24 reported impaired anterior and posteromedial
injuries.10–12 Research suggests deficits in static and dynamic reach in individuals with chronic ankle instability and
balance discern between individuals with a history of ankle Herrington et al17 found significant differences in anterior,
sprains, chronic ankle instability, anterior cruciate ligament posteromedial, medial, and lateral reach in patients with
(ACL) deficiency, and anterior knee pain.13–17 In addition, ACL-deficient knees as compared to age-matched controls.
exercise programs focused on balance training have also been Previous research using factor analysis also suggests shared
variance and redundancy occur between the eight reach
directions of SEBT in healthy controls and individuals with
chronic ankle instability.25
*U.S. Army-Baylor University Doctoral Program in Physical Therapy,
ATTN: MCCS-HGP, 3599 Winfield Scott Road, Suite 1301, Fort Sam Houston, The Y-balance test (YBT) has built on previous research
TX 78234-6138. suggesting redundancy in the 8 directions of the SEBT to
†Telemedicine and Advanced Technology Research Center, U.S. Army develop a more time-efficient test that evaluates dynamic
Medical Research and Material Command, ATTN: MCMR-TT, Building limits of stability and asymmetrical balance in only three
1054 Patchel Street, Fort Detrick, MD 21702. directions (anterior, posteromedial, and posterolateral).27–29
This work was presented as a poster at the 2011 American Physical
Therapy Association, Combined Sections Meeting, New Orleans, LA,
Initial evidence on the YBT for injury prediction is encour-
February 2011. aging. Specifically, Plisky et al10 identified that individuals
doi: 10.7205/MILMED-D-13-00222 with anterior left/right asymmetries greater than 4 cm on the

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 Y-Balance Test: A Reliability Study Involving Multiple Raters

YBT were 2.5 times more likely to sustain a lower extremity loskeletal disorders that limited participation in work or exer-
injury. The YBT and SEBT have also exhibited acceptable cise in the last 6 months. Participants were excluded if they
intrarater reliability among two raters intraclass correlation were currently seeking medical care for lower extremity inju-
coefficients (ICC, 0.67–0.96), but a wide range of interrater ries or had previous medical history that included any surgery
reliability with point estimate ICC values ranging from for lower extremity injuries. Participants were also excluded
0.35 to 1.30 In addition, previous reliability assessment specific if they were unable to participate in physical training because
to the YBT was established with only two raters with a mini- of other musculoskeletal injuries, had a history of a pelvic or
mum of at least 7 years of clinical experience.29 Traditionally, lower extremity fracture, or were pregnant. All participants
mass screenings of athletes or service members require a larger who agreed to participate and met inclusion criteria signed an
number of examiners and the examiners available for such informed consent form approved by Brooke Army Medical
screenings may vary day to day. Center’s Institutional Review Board and returned 48 hours

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Effective and efficient injury screening requires measure- later for data collection.
ment tools that show reliability in a larger population screen-
ing setting using multiple raters with limited experience.
Therefore, the primary purpose of this study was to assess Raters
the interrater test–retest reliability of the YBT among a group The raters in this study consisted of 7 entry-level doctoral
of raters with limited health care or injury screening experi- physical therapy students. Before testing, all raters underwent
ence. In addition, previous YBT reliability research has used training that consisted of approximately 10 hours of hands-on
the maximum reach distance over 3 trials.29 Considering that training with the equipment and technique of the 15 tests led
maximum performance may significantly vary between raters by 4 physical therapy faculties and a research assistant. To
and ultimately influence reliability, our secondary purpose minimize bias, the participants were randomly assigned to one
was to assess both maximal and mean YBT performance. of 3 raters on day 1 and one of 4 raters on day 2 (24–48 hours
Limited information on YBT performance in service members later). All participants were assessed by a different randomly
also exists. Therefore, the final purpose of this study was assigned rater on day 2 who were blinded to day 1 results.
to describe YBT performance and to determine the proportion The goal of having random sets of raters blinded to previous
of service members with a YBT anterior reach limb asymmetry results for each assessment was to increase the variability
(>4cm difference) based on its association with increased in the study design and to more closely mimic field conditions
injury risk.10 in the military and athletic mass screening settings. There were
no significant difference between raters; therefore, data was
METHODS aggregated for analysis.
The YBT was one of 15 counterbalanced measures collected
as part of a lower extremity injury prevention screening Measurements
examination conducted at Fort Sam Houston, TX.9,31 Testing The YBT consists of a three-part test that is used to assess
was completed in a group setting with multiple raters and
lower extremity balance and neuromuscular control to predict
participants were tested on separate days by independent
lower extremity injury.30 Each participant viewed a YBT
examiners to assess both the influence of different raters and
instructional video and performed 6 practice trials to mini-
time. Participants were also given 24 to 48 hours between
mize the influence of a learning effect.32 After the instruc-
measures to reduce the influence of fatigue from multiple
tional video, participants stood on the center footplate, with
station testing. All testing was performed in the morning
the distal aspect of the right foot at the starting line (Fig. 1).
between 6:00 a.m. and 10:00 a.m. This time was selected based
While maintaining single leg stance on the right leg, the
on traditional physical training hours for military personnel.
subject reached with the free limb (left leg) in the anterior
(Fig. 2), posteromedial (Fig. 3), and posterolateral (Fig. 4)
Participants directions in relation to the stance foot by pushing the indica-
The convenience sample included participants that were tor box as far as possible. Participants completed 3 consecu-
recruited over an 8-week period from service members tive trials for each reach direction and to reduce fatigue
attending various initial training at Fort Sam Houston, TX. subjects altered limbs between each direction. Specifically,
Potential participants were provided an overview of the testing order was completed as right anterior, left anterior,
research study, and specific details of the entrance criteria right posteromedial, left posteromedial, right posterolateral,
was discussed before consenting. Every potential participant and left posterolateral. Attempts were discarded and repeated
completed an injury screening form to review inclusion and if the subject failed to maintain unilateral stance on the plat-
exclusion criteria. Participants were eligible for inclusion form, failed to maintain reach foot contact with the reach
if they were between the ages of 18 and 35 years or emanci- indicator on the target area while the reach indicator is in
pated minors, fluent in English, had no current complaint motion, used the reach indicator for stance support, or failed
of lower extremity or spine pain, or medical or neuromuscu- to return the reach foot to the starting position under control.

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FIGURE 1. Starting position Y-balance test.
FIGURE 3. Posteromedial reach Y-balance test.

FIGURE 2. Anterior reach Y-balance test.

FIGURE 4. Posterolateral reach Y-balance test.

Participants were allowed a maximum of 6 trials to obtain

3 successful trials for each reach direction.29,32 assigned rater. In addition, reach distance was recorded to the
The maximal and average distance reached after 3 success- nearest 0.5 cm. Subject’s lower limb reach was also normalized
ful trials in each direction were recorded at baseline by the rater to leg length, which was measured from the anterior superior
and approximately 48 hours later by the second randomly iliac spine to the most distal portion of the medial malleolus.

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 Y-Balance Test: A Reliability Study Involving Multiple Raters

Data Analysis difference in reach distances between limbs ( p > 0.05), 31.3%
Maximal and average reach over 3 trials were analyzed for (n = 20 of 64) of the subjects had an anterior reach asymme-
both limbs in the anterior, posteromedial, and posterolateral try of greater than 4 cm suggesting balance asymmetry and
reach directions. Reach distances were calculated as both abso- potentially increased risk for injury based on a previously
lute reach values and reach values normalized to limb length to published risk index.10
allow comparisons across subjects and to previous publica- Interrater test–retest reliability for the maximal reach
tions. To express reach distance as a percentage of limb length, had good ICC (2,1) values that ranged from 0.80 to 0.85
the normalized value was calculated as reach distance with an associated SEM ranging from 3.1 to 4.2 cm and
divided by limb length then multiplied by 100%. Composite MDC values ranging from 8.7 to 11.5 cm for the 3 reach
reach distance was the sum of the 3 reach directions divided directions. Interrater reliability for the average of 3 reaches
by 3 times limb length, and then multiplied by 100%. Descrip- in each direction also showed good reliability (ICC (2, 3)

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tive statistics (means, standard deviations, 95% confidence values = 0.85–0.93) and measurement error (SEM = 2.0–
intervals) were calculated for composite reach distance and 3.5 cm and MDC values = 5.5–9.7 cm) for the 3 reach direc-
each reach distance for both limbs. Paired t tests were used to tions (Table III).
determine if there was a significant ( p < 0.05) difference
between the performance of the right and left limb. In addi-
DISCUSSION
tion, asymmetry between reach distances and the number of
Our results in actively training service members provides
individuals with anterior asymmetry >4cm was calculated.
initial evidence to suggest that the YBT is reliably obtained
Reliability of the maximal reach and average of 3 reach
in a mass screening setting by multiple raters across a 48-hour
trials was analyzed using ICC. The maximal reach was ana-
period. Findings also build on past literature suggesting that
lyzed using the ICC (2,1) model and the average of 3 trials
the SEBT and specifically YBT are reliable measures of
was analyzed using the ICC (2,3) model. Good reliability was
postural control in active younger adults.30 Hertel et al28
defined as 0.75 or higher, moderate as 0.50 to 0.74, and poor
showed poor to good day 1 interrater reliability and good
as less than 0.49.33 Response stability and precision were
day 2 interrater reliability (ICC = 0.81–0.93) when using
analyzed by calculating standard error of measurement (SEM)
two experienced raters conducting independent assessments.
and minimal detectable change (MDC) values at the 95%
Authors did not use practice trials and concluded that limited
confidence level. SPSS for Windows, version 16.0 (SPSS,
Chicago, IL) statistical software was used to analyze the data. day 1 interrater reliability was likely the result of a significant
learning effect seen between the first 6 trials measured. Plisky
et al,29 using 6 practice trials, reported almost perfect (0.97–
RESULTS 1.00) interrater reliability; however, the raters in the Plisky
A total of 64 participants (53 males, 11 females) were study were observing the same trials. Interestingly, our inter-
enrolled and completed this study (Table I). No participants rater test–retest reliability that was conducted by multiple
were excluded from this analysis. There was no significant pairs of independent raters and on separate days closely
reach difference between limbs and days ( p > 0.05); there- matched the test–retest (one rater taking repeat measurements
fore, outside of the descriptive data (Table II), all reach dis- 20 minutes apart on the same day) ICC values obtained by
tances unless otherwise stated are in reference to day 1 data Plisky et al.29 In particular, our ICC values for specific max-
of the right lower extremity. On average, service members imal and mean reach distances ranged from 0.80 to 0.93 with
showed a 57.6 ± 7.1 cm anterior reach, 92.5 ± 9.0 cm SEMs from 2.0 to 4.2 cm. The test–retest reliability for the
posteromedial reach, and 89.1 ± 9.4 cm posterolateral reach. study of Plisky ranged from 0.85 to 0.88 with SEMs from
These absolute reach values corresponded to normalized
2.0 to 3.1 cm. Although direct comparison of results is limited
reach values of 63.5%, 102%, and 98.2% of limb length
secondary to different testing days, number, and experience
in the anterior, posteromedial, and posterolateral reach direc-
of raters, our findings reinforce previous YBT reliability
tions, respectively. The descriptive statistics of the maximal
research and provide initial evidence that suggests the YBT
reach and average reach of 3 trials of both limbs are reported
has acceptable reliability and measurement stability between
in Table II. Although there was no significant group mean
multiple raters with limited experience.
The interrater test–retest design we employed using multi-
TABLE I. Demographics
ple raters mimicked real-world preseason or predeployment
Type Mean ± SD 95%CI screenings. In particular, our examiners were required to each
Age (years) 25.2 ± 3.8 24.3–26.2 independently instruct and score the YBT performance. An
Height (cm) 175.5 ± 9.6 173.1–177.9 additional potential confounding variable was time as rater’s
Weight (kg) 77.5 ± 12.5 74.4–80.7 assessments were conducted 48 hours apart. Despite these
Body Mass Index (kg/m2) 25.1 ± 3.1 24.3–25.9 potential sources of error, reliability between multiple raters
Limb Length (cm) 92.2 ± 5.9 90.8–93.7
and multiple days was maintained in a sample of 64 active
SD, standard deviation; CI, confidence interval. duty service members.

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 Y-Balance Test: A Reliability Study Involving Multiple Raters

TABLE II. Y-Balance Test Descriptive Statistics

Absolute Reach (cm) Normalized Reach (%)

Type Direction Lower Extremity Mean ± SDa (95% CI) Mean ± SDa,b (95% CI)
Maximal Reach Anterior Left 60.0 ± 7.4 (58.2,61.8) 66.0 ± 7.8 (64.2,68.0)
Right 59.8 ± 7.1 (58.1,61.5) 65.8 ± 7.6 (64.0,67.7)
Posteromedial Left 95.7 ± 8.3 (93.7,97.7) 105.3 ± 8.3 (103.4,107.3)
Right 95.0 ± 8.7 (92.9,97.1) 104.6 ± 8.9 (102.5,106.7)
Posterolateral Left 91.3 ± 8.5 (89.2,93.3) 100.5 ± 9.1 (98.4,102.7)
Right 92.1 ± 9.4 (89.8,94.3) 101.4 ± 9.6 (99.1,103.7)
Composite Left 246.9 ± 21.8 (241.7,252.2) 90.6 ± 7.5 (88.8,92.4)
Right 246.8 ± 23.0 (241.3,252.4) 90.6 ± 7.9 (88.7,92.5)

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Average Reach of 3 Trials Anterior Left 57.8 ± 6.8 (56.1,59.4) 63.6 ± 7.2 (61.9,65.3)
Right 57.6 ± 7.1 (55.9,59.3) 63.5 ± 7.7 (61.6,65.3)
Posteromedial Left 93.2 ± 8.5 (91.2,95.3) 102.7 ± 8.6 (100.6,104.8)
Right 92.5 ± 9.0 (90.4,94.8) 102.0 ± 9.4 (99.7,104.2)
Posterolateral Left 88.3 ± 8.5 (86.2,90.3) 97.2 ± 9.4 (95.0,99.5)
Right 89.1 ± 9.4 (86.9,91.4) 98.2 ± 10.0 (95.8,100.6)
Composite Left 239.3 ± 21.5 (234.1,244.4) 87.8 ± 7.6 (86.0,89.7)
Right 239.4 ± 23.5 (233.7,245.0) 87.9 ± 8.3 (85.9,89.9)

CI, confidence interval; SD, standard deviation. aValues represent mean ± standard deviation (95% confidence interval). bNormalized reach was calculated
as reach distance/limb length(anterior superior iliac spine to medial malleolus) 100.
+

In contrast to previous YBT literature,10,29 our study explanation for these findings includes the fact that our sub-
investigated both maximal and mean performance and its jects were slightly older (mean age = 25.2 years), and
influence on reliability. Interrater test–retest reliability was although actively running and performing push-ups and sit-
good for both maximal and mean YBT reach distance, with ups, our subjects were not required to take part in sporting or
the average of 3 reaches having superior ICC, SEM, and recreational activities.
MDC values. In particular, the use of mean versus maximum The final purpose of our study was to identify the percentage
values resulted in approximately a 1 cm decrease in individ- of U.S. service members with anterior reach limb asymmetries.
ual SEM reach differences and a 2 cm decrease in composite Similar to Plisky et al10 who examined 245 individuals and
reach distance. The use of 3 trials to obtain a mean reach found 31.9% with anterior limb asymmetries, our study
distance value has also been reported by other studies.25,32,34 revealed 31.3% of military service members with greater than
In addition to both maximal and mean YBT scores in our a 4-cm difference in anterior limb reach distance. Although
study showing good reliability, measurement stability was specific injury-predictive cut scores have not been identified
improved when averaging 3 trials. Considering that 6 practice in a military population, these findings do reinforce that
trials and 3 test trials are recommended to reduce a learning almost one-third of our sample had asymmetric dynamic
effect on the YBT,30,35 practitioners and researchers should balance in the anterior sagittal plane. Whether these balance
continue to evaluate the potential utilization and validity asymmetries in actively training service members lead to
of both maximal and mean YBT performance. injuries has yet to be determined.
YBT-normalized anterior reach performance for military Some limitations to our study do exist. First, our study was
members in our sample was less than those identified in a limited to actively training service members involved in
sample of college-age students (mean ± SD = 80 + 11%) and initial entry training, thus potentially limiting the external
high school athletes (mean + SD = 83 ± 7.1%).10,25 Potential validity and generalization of our findings to all military

TABLE III. Y-Balance Test Interrater Reliability

Type Direction ICC (95%CI) SEM (cm) MDC (cm)

Maximal Reach ICC (2,1) Anterior 0.82 (0.72,0.89) 3.1 8.7
Posteromedial 0.81 (0.71,0.88) 3.7 10.3
Posterolateral 0.80 (0.68,0.87) 4.2 11.5
Composite 0.85 (0.76,0.91) 9.0 24.8
Average Reach of 3 Trials ICC (2,3) Anterior 0.93 (0.88,0.96) 2.0 5.5
Posteromedial 0.91 (0.85,0.94) 2.7 7.5
Posterolateral 0.85 (0.75,0.91) 3.5 9.7
Composite 0.91 (0.85,0.95) 7.0 19.5

CI, confidence interval; ICC, intraclass correlation coefficient; SEM, standard error of the measurement; MDC, minimal detectable difference (95%).

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 Y-Balance Test: A Reliability Study Involving Multiple Raters

populations (e.g., Rangers, Seals, Special Forces). Second, sub- 8. Ruscio BA, Jones BH, Bullock SH, et al: A process to identify military
jects in our sample were screened with medical questionnaires injury prevention priorities based on injury type and limited duty days.
Am J Prev Med 2010; 38: S19–S33.
and all participants had to fully squat and hop on one limb 9. Teyhen DS, Shaffer SW, Lorenson CL, et al: The Functional Move-
without pain before inclusion. Conducting the YBT in popu- ment Screen: a reliability study. J Orthop Sports Phys Ther 2012;
lations that have not undergone additional medical screening 42: 530–40.
may ultimately result in increased abnormal YBT asymmetries. 10. Plisky PJ, Rauh MJ, Kaminski TW, Underwood FB: Star Excursion
Future research examining the YBT in the general popu- Balance Test as a predictor of lower extremity injury in high school
basketball players. J Orthop Sports Phys Ther 2006; 36: 911–9.
lation when used in mass screenings, as well as in different 11. Vrbanic TS, Ravlic-Gulan J, Gulan G, Matovinovic D: Balance index
military and athletic populations, may enhance the external score as a predictive factor for lower sports results or anterior cruciate
validity of the YBT. Additional study involving the predic- ligament knee injuries in Croatian female athletes: preliminary study.
tive validity of the YBT to determine future injuries is also Coll Antropol 2007; 31: 253–8.

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needed. Finally, research that establishes the responsiveness 12. Trojian TH, McKeag DB: Single leg balance test to identify risk of ankle
sprains. Br J Sports Med 2006; 40: 610–13.
and influence of treatment techniques on YBT performance 13. Aminaka N, Gribble PA: Patellar taping, patellofemoral pain syndrome,
in military-specific populations appears warranted. lower extremity kinematics, and dynamic postural control. J Athl Train
2008; 43: 21–8.
14. Akabari M, Karimi H, Farahini H, Faghihzadeh S: Balance prob-
CONCLUSIONS lems after unilateral lateral ankle sprains. J Rehabil Res Dev 2006;
Among multiple raters with limited health care experience, 43: 819–24.
the YBT showed good interrater test–retest reliability and 15. Gribble PA, Hertel J, Denegar CR, Buckley WE: The effects of fatigue
minimal levels of measurement error. The YBT had good and chronic ankle instability on dynamic postural control. J Athl Train
2004; 39: 321–9.
interrater test–retest reliability for both the maximal and
16. Gribble PA, Hertel J, Denegar CR: Chronic ankle instability and fatigue
average of 3 reaches. The measurement error was mini- create proximal joint alterations during performance of the Star Excur-
mized and interrater test–retest reliability improved when sion Balance Test. Int J Sports Med 2007; 28: 236–42.
the mean of 3 reach trials was used. Although, our partici- 17. Herrington L, Hatcher J, Hatcher A, McNicholas M: A comparison of
pants underwent screening before participation, 31.3% of Star Excursion Balance Test reach distances between ACL deficient
patients and asymptomatic controls. Knee 2009; 16: 149–52.
military members exhibited greater than a 4-cm asymmetry
18. Emery CA, Rose MS, McAllister JR, Meeuwisse WH: A preven-
on the anterior reach YBT. Additional research in various tion strategy to reduce the incidence of injury in high school basket-
military and athletic populations examining the predictive ball: a cluster randomized controlled trial. Clin J Sport Med 2007; 17:
validity, responsiveness, and the influence that training has 17–24.
on YBT scores is needed. 19. McGuine TA, Keene JS: The effect of a balance training program on
the risk of ankle sprains in high school athletes. Am J Sports Med 2006;
34: 1103–11.
ACKNOWLEDGMENTS 20. Benjaminse A, Habu A, Sell TC, et al: Fatigue alters lower extremity
kinematics during a single-leg stop-jump task. Knee Surg Sports
This study was done in collaboration with research assistants from the Uni-
Traumatol Arthrosc 2008; 16: 400–7.
versity of Texas Health Science Center and U.S. Army-Baylor University, 21. Myer GD, Ford KR, McLean SG, Hewett TE: The effects of plyometric
Departments of Physical Therapy. The authors also want to thank Jennifer versus dynamic stabilization and balance training on lower extremity
Prye for her assistance with manuscript preparation. biomechanics. Am J Sports Med 2006; 34: 445–55.
22. Myer GD, Ford KR, Brent JL, Hewett TE: The effects of plyometric
vs. dynamic stabilization and balance training on power, balance,
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