The Y Balance Test: Assessing the evidence | Lower Extremity Review Magazine (2024)

The Y Balance Test (YBT) is a reliable tool and may be used to predict injury risk. However, clear cut-points have not been sufficiently defined, and more research investigating the mechanics and muscle activation strategies used during the YBT is needed.

By Craig A. Smith, DPT, and Meghan Warren, PT, MPH, PhD

Dysfunctional, limited, or asymmetrical control in single-leg balance tasks have been associated with increased injury risk during participation in sport^1-3 and have been shown to discriminate between individuals with and without previous anterior cruciate ligament injuries⁴ or chronic ankle instability.^5,6

In the literature, two related tests have been used to assess performance during single-leg balance tasks: the Star Excursion Balance Test (SEBT) and the Y Balance Test (YBT). The SEBT was originally described by Gray et al⁷ as a series of single-leg squats on the stance limb with the contralateral limb reaching on a line in one of eight directions. In an effort to reduce redundancy and improve efficiency, the SEBT was modified from the eight original directions to only the anterior, posteromedial, and posterolateral reach directions.^2,6 A literature review of the original and modified versions of the SEBT found it is a reliable and valid noninstrumented tool for effectively assessing dynamic single-leg balance.⁸

An instrumented version of the SEBT, the YBT, was created to improve repeatability by standardizing the protocol and eliminating areas that reduced accuracy, using the SEBT as a model in the same three reach directions.⁹ The SEBT is performed on a flat surface with reach lines laid in the three directions. Distance is determined by a light touch to the ground of the most distal portion of the reaching foot. In contrast, the YBT instrument has a central raised platform with three pieces of PVC (polyvinyl chloride) pipe in the three directions with a sliding plastic reach indicator that the participant pushes to determine reach distance (Figure 1).⁹

It is common to use the SEBT and YBT interchangeably without clear differentiation between protocols¹⁰ or to combine them; for example, when implementing the SEBT using the YBT protocol.¹¹ The similarities in protocol and design have encouraged the use of evidence that is specific to the SEBT to support the use of the YBT; this, however, may not be appropriate. In the only two investigations comparing the SEBT with the YBT,^12,13 differences between the tests were found for reach distance achieved and kinematics, despite the aforementioned similarities. Coughlan et al¹² and Fullam et al¹³ suggested that research conducted using the SEBT may not be transferable to the YBT.

Since the YBT is relatively new,⁹ the number of studies utilizing it specifically is small compared with the number of studies utilizing the SEBT.⁸ The majority of the evidence concerned with the YBT involves sports^14-17 and injury association,^11,18,19 with conclusions that have supported cut-points and normative values specific to sport, gender, and previous injury history. Obviously, the use of instrumented and noninstrumented versions of the SEBT is another important consideration. Therefore, the purpose of this brief literature review is to evaluate the evidence specific to the YBT.

Protocol and reliability

The development of the YBT protocol was meant to improve repeatability by addressing variations in protocol and sources of error.⁹ To do this, an instrument was created to perform the reach directions along pipes using reach indicators that clearly marked the reach distance in anterior, posteromedial, and posterolateral directions. The YBT protocol, unlike the SEBT protocol, allowed stance foot movement. This change was in response to the difficulty experienced by test administrators related to tracking the movement of the reaching leg while simultaneously monitoring for foot movement of the stance leg.

Performance on the SEBT was noted to plateau after several practice attempts. In the original description of the YBT, Plisky et al⁹ endeavored to control for the effects of motor learning by analyzing previously published SEBT evidence with regard to the number of practice attempts.²⁰ Recent research on the SEBT indicated that four reaches, instead of six, could be used during the practice sessions.²¹ The use of an instrument and an instructional video prior to testing as described by Plisky et al⁹ may reduce the amount of practice reaches required during testing. To date, no study has investigated the number of reaches required for plateau using the YBT. It is possible that fewer practice reaches can be used, which would facilitate obtaining reliable and valid results in a timely manner.

The YBT testing protocol assessed absolute reach and normalized distance for each direction, asymmetry between limbs, and composite score. Normalized reach distance is calculated by dividing reach distance by the limb length. Asymmetry is the absolute difference between right and left leg and is determined for each reach direction. The composite score is calculated by summing the reach distance in the three directions, dividing by three times limb length, and multiplying by 100.^2,9

Three studies have investigated the reliability of the YBT. Plisky et al⁹ found good to excellent interrater reliability (intraclass correlation coefficient [ICC] equal to .99 to 1 with 95% confidence intervals [95% CI] ranging from .92 to 1) and intrarater reliability (ICC of .85-.91 with 95% CI ranging from .62 to .96). The raters in that study were a physical therapist and athletic trainer, each with more than seven years of experience, and the study population was a small sample of 15 soccer players. Shaffer et al²² built on this, reporting good interrater reliability with ICC equal to .85 to .93 (95% CI, .75-.96) and test-retest reliability with ICC equal to .80 to .85 (95% CI, .68-.91); that study involved multiple raters with limited experience and testing done over multiple days in a larger sample of 64 military service members.

Faigenbaum et al²³ investigated interrater reliability on two levels, for observer error and for performance error. Observer error referred to raters observing and scoring the same participant at the same time, while performance error referred to raters observing the same participant on the same day but at different times. Faigenbaum et al²³ reported an ICC greater than .995 for observer error measurement and a range from .91-.99 for performance error measurement. Intrarater reliability was found to be moderate to good.

Normative data

Normative YBT data have been collected in children,²³ competitive soccer players,²⁴ adolescent males in Rwanda and the US,²⁵ military service members,^22,26 and baseball players with and without ulnar collateral ligament (UCL) injuries.¹⁵ Data have also been collected on collegiate Division I athletes¹⁹ and a Division III football cohort¹¹ during investigations of YBT performance and injury association (Table 1).

Injury history, age, sex, and geographic location appear to affect YBT testing results and performance. An interesting investigation into the effect of regional interdependence and the kinetic chain by Garrison et al¹⁵ found that YBT performance in athletes suffering from an UCL injury was impaired compared with those without the same injury. Since the athletes were not tested prior to having the injury, it is not clear if the decrease in performance was a result of the injury or if it contributed to the occurrence of the injury. The authors hypothesized that the YBT performance may indicate an inefficient lower extremity motor pattern that could change throwing and pitching mechanics, leading to upper body injury.

In a large group of students in the first through fifth grades (n = 188), reach distance gradually increased with grade level.²³ Since distances were not normalized to limb length, it is not possible to determine if this was because older children had better performance than younger children, if the older children were taller, or if a combination of both conditions influenced results.

A comparison of male soccer players at high school, college, and professional levels found the greatest anterior reach distances in the high school athletes—contrary to the authors’ hypothesis that a higher level of competition would correlate with better performance. However, the college and professional cohort performed greater reach distances than the high school athletes for the posteromedial and posterolateral directions. Injury history was not collected on the participants; therefore possible explanations for the 4% difference in anterior reach direction between the high school and the college and professional cohort could not be investigated in greater depth.

Adolescent male soccer players from Rwanda outperformed an age- and sex-matched sample from the US in all YBT reach directions.²⁵ The Rwandan adolescents’ composite score was 105.6 ± 1.3% compared with 100.9 ± .8% and 101.8 ± 1.2% for the aforementioned college and professional cohorts, respectively, suggesting that geographical location may be as important to consider as competition level.

Gorman et al¹⁶ found no difference in YBT performance between athletes involved in one or multiple sports. However, they found that male athletes outperformed female athletes for the posteromedial and posterolateral reach directions, as well as for composite score. Similarly, Teyhen et al²⁶ found that male athletes and those younger than 30 years demonstrated better performance on the YBT than female athletes and those older than 30 years.

When examined collectively, male athletes consistently outperform female athletes, even with normalization of reach distance. Age may influence performance in a bell curve, with improved performance over time until individuals are aged 30 years, when a decrease in reach distance is seen. More research is needed in differently aged populations to support this trend.

Current injury resulted in lower composite scores,¹⁵ but other evidence suggests previous injury does not appear to reduce reach distance. While the majority of the aforementioned studies did not collect injury history,^14,16,24,25 a large multisport cohort study found no association between previous injury history and YBT composite score.²⁷ Further, after UCL surgery, baseball players improved from a 89.4 ± 7.5% composite score on the stance leg to 94.9 ± 9.5% at three months postsurgery.¹⁷ The stance leg composite score in the injured group at three months postsurgery was comparable to that of the control group from the earlier UCL study (95.4 ± 6.4%),¹⁵ which was performed by the same research group.

Finally, asymmetry in reach distance between limbs has been consistently reported for all three reach directions.^16,22,24,25 In one study, anterior reach asymmetry greater than 4 cm was found in 31.3% of participants;²² asymmetries of this magnitude may be clinically significant with respect to increased injury risk.¹⁹

Injury research

Prior to the creation of the YBT, Plisky et al² found that lower extremity injury risk was associated with SEBT composite scores below 94% and anterior reach asymmetry greater than 4 cm. YBT performance and injury risk has been assessed in football players¹¹ and in a Division I multisport cohort.¹⁹ Butler et al¹¹ determined that composite score below 89.6% increased risk of noncontact lower extremity injury by 3.5 times (95% CI, 2.4-5.3) in a collegiate football cohort; however, they found no relationship between reach asymmetry and injury risk. In contrast, Smith et al¹⁹ found no relationship between composite score and injury risk, while anterior reach asymmetry greater than 4 cm increased the odds of injury by 2.2 (95% CI, 1.1-4.5). Beyond the difference in samples, injury was defined differently in each study, which limited comparison. Further, Smith et al¹⁹ did not investigate sport-specific cut-points, as the purpose of the study was to determine a single cut-point across multiple sports. Based on the findings of Butler et al,¹¹ research investigating sport-specific cut-points may be valuable. However, because there are significant differences between positions within certain sports, such as football, this may not be sufficient differentiation.

Finally, an algorithm was created that includes YBT reach asymmetry and composite score, the Functional Movement Screen, demographic information, previous injury history, and presence of pain to identify possible associations with injury.¹⁸ The weight of YBT performance within the algorithm was not reported, however, the authors stated that the risk threshold was determined by competition level, sex, and sport. Athletes placed in the high-risk category were 3.4 (95% CI, 2-6) times more likely to experience injury.

YBT and SEBT comparison

Coughlan et al¹² and Fullam et al¹³ found significant differences in the anterior reach kinematics and distance between the YBT and SEBT. The initial investigation found that participants reached farther in the anterior reach component of the SEBT than in the anterior reach component of the YBT.¹² This led the authors to conclude the two tests may involve different motor strategies as a result of the differences in instrumentation and protocol specifics. A follow-up investigation into the kinematics found that, in the anterior reach direction, more hip flexion was present at the maximum reach distance for the YBT than the SEBT.¹³

Interestingly, increased SEBT anterior reach distance was correlated with reduced hip flexion, meaning that, as the angle at the hip joint increased, the reach distance decreased (Figure 2). The opposite occurred with the YBT, meaning that, as the angle at the hip joint increased, the reach distance also increased (Figure 1). This supports the previous conclusion that different strategies are used in the two tests. Therefore, previous SEBT literature concerning anterior reach kinematics and muscle activation may not be applicable to the YBT. Further kinematic and muscle activation data must be collected using the YBT.

Conclusion

The YBT is a reliable tool among raters with various experience and background. Normative data indicate differences in YBT performance related to sex, age, injury, geographic location, and competition level. The YBT may be used to predict injury risk; however, clear cut-points have not been sufficiently defined. The differences between the SEBT and YBT indicate that more research investigating the mechanics and muscle activation strategies used during the YBT is needed. No research to date has investigated kinematic or muscle activation differences between individuals with decreased composite score or asymmetry in reach and those with normal YBT scores.

Craig A. Smith, PT, DPT, is a practicing physical therapist in Tucson, AZ, director of the Performance Project at Proactive Physical Therapy in Tucson, and an adjunct faculty member at Northern Arizona University in Flagstaff. Meghan Warren, PT, MPH, PhD, is an associate professor of physical therapy at Northern Arizona University.

Disclosure: The authors of this article have no conflict of interest to report.