Star Excursion Balance Test & Dynamic Postural Control

This post is via Rayner & Smale

The Star Excursion Balance Test (SEBT) is one of my favourite dynamic balance assessment tools and this blog covers the construct and current literature existing around it's use. The SEBT is not an injury-specific test and has been the subject of research for almost 20 years, and was first described in 1998 (Gribble, Hertel & Plisky., 2012). 

Researchers are continually driven to investigate biomechanical and neuromuscular factors contributing to initial injury and recovery. Especially in conditions such as non-contact ACL injuries and the development of chronic ankle instability. The SEBT has gained popularity from it's ability to detect postural control deficits between limbs and between healthy controls and injured populations. In addition to identifying dynamic balance deficits in a variety of conditions, the SEBT is also responsive to changes in dynamic balance from training programs (Gribble, Hertel & Plisky., 2012).   

THE SEBT

The SEBT was originally described as a rehabilitation tool consisting of a patient balancing on one leg and repeatedly performing single leg squat movements to use the non-stance leg to reach maximally along one of eight diagonal lines, each at 45 degree intervals from each other (Gribble, Hertel & Plisky., 2012). Participants are instructed to touch all 8 lines 6 times before measurements were made.

There is no argument that the SEBT is both reliable and valid in assessing dynamic balance (Hyong & Kim., 2014), however, over time, as studies investigated the reliability and validity of this test, they came to realise that test-redundancy occurred, as well as the learning effect. What these two terms mean is that we needed to study how many times was truely necessary for the test to be taken, and, how many lines were needed to produce the most relevant outcomes. This has lead to modifications in the original test procedure.

In generally, 4 trials are now recommended in both clinical and research settings, to allow for the learning effect to occur and measurement error to be reduced (Gribble, Hertel & Plinky., 2012). Researchers have also found that not all 8 directions are needed to gain valuable data from the test. There was a huge amount of shared variance found between all 8 lines, meaning that an individuals ability to reach in one direction was highly correlated to another (Hertel, Braham, Hale & Olmsted-Kramer., 2006 p.135). This has been referred to as test-redundancy and the outcome of this information is that the test has now been simplified to 3 directions - anterior, posteromedial, and posterolateral - and this test can be referred to as the modified SEBT or Y balance test.  

Y balance test. Courtesy of Google Images

Standardised testing (Gabriner, Houston, Kirby & Hoch., 2015; Gribble, Hertel & Plinky., 2012):

• Anterior (ANT), posteromedial (PM) and posterolateral (PL) lines.
• Stand on the central point.
• Hands on hips. 
• Reach as far as you can along the line and gently tap the line.
• Do not come to rest on the line.
• Do not transfer your body weight onto the reaching leg.

The thing that interests me is that the research trials strongly emphasise standardisation of testing, to create a reliable measure and interpretation of the reach/distance outcome. This is fair and probably results in a more accurate measure of distance. Yet, none of them teach us how to interpret movement patterns or retrain them, which is what I find the test more valuable for. 

After reading the research and reviewing my own video below, it is clear that I don't place as much emphasis on hand placement as I do dynamic knee control. I also don't perform the strict 4 trials. Maybe this can be explained by time restrictions, or that I use the test to train dynamic balance rather than focussing on a pure measurement? When I conduct the test I will normally do it twice. The first time I film and observe the movement. Then I coach the patient. Then I measure their second attempt. 

How many times do your patients perform the test?
Are your specific on instructing it in a standardised way? 
Why are you using it?

FACTORS AFFECTING PERFORMANCE 

It is commonly understand that reach distance is going to be impacted by size, limb length and sex too. This is probably why there aren't too many studies telling us how far someone should be able to reach. Rather there is a percentage difference between limbs or between injured and control populations. Below are two additional considerations that I read about which impact performance on this test.

Foot placement:

Whether you place your heel on the central point (usually done for anterior reach) or toe on the central point (for PM and PL) will change the outcome of your test. Be mindful about consistency in foot placement. “Only focussing on the results without considering different foot alignment may lead to misinterpretation of the findings, especially for anterior reach scores” (Cut., 2017, p.5). 

While foot placement may affect the results, no significant reaching differences have been detected when researchers looked at arch control. In some cases having a flat foot or loss of arch control allowed one to reach further in the PL direction but no conclusive results were found. As such, it is not recommended to control for foot type, but rather to consider the arch control as a part of the whole picture and dynamic balance performance of that stance limb (Gribble, Hertel & Plinky 2012). 

Muscle activation patterns:

A study was conducted in 2001 by Earl & Hertel and later summarised in the systematic review by Gribbel et al (2012), which looked at the different thigh muscles contributing to balance during different reach directions. They found that:

• Vastus medialis is most active in anterior reach. 
• Vastus lateralis is least active in lateral reach.
• Medial hamstring is most active during anterolateral reach.
• Bicep femoris was most active during posterior and posterolateral reach. 

These reach directions seem to be the opposite to the location and line of pull of each muscle, which makes sense if they are working to control center of mass. It is always great to come across studies like this that help guide our clinical reasoning and the key message here is that if we want to train specific muscles, we can use targeted reach directions to bias them. 

WHAT DOES THE SEBT TELL US?

The most significant change to the structure of the SEBT is reducing 8 lines to 3. What this has lead us to investigate is the movement patterns and physical limitations which impact each of these three directions. Here are some stats that consistently appear in the research across different patient populations:

CHRONIC ANKLE INSTABILITY (CAI):

• In CAI, all three directions have the ability to identify reach deficits in participants compared to healthy controls, however, the PM is the most representative of the overall performance (Hertel, Braham, Hale & Olmsted-Kramer., 2006). 
• These shorter reach distances can be a combination of different factors, either mechanical or sensorimotor in nature (Gabriner, Houston, Kirby & Hoch., 2015 p.912). These authors found that with CAI, different directions require different physical demands. 
  • Anterior reach is more impacted by dorsiflexion ROM and plantar cutaneous sensation, meaning that mechanical restrictions and sensory deficits impact this movement.
  • DF ROM is best evaluated with the knee to wall weight bearing lunge test compared to non weight bearing AROM (Dill et al., 2014). 
  • Posteromedial and posterolateral reach is more impacted by eversion strength and balance control. 
• De la Motte, Arnold & Ross (2015) studied the movement pattern differences in trunk rotation and found that patients with CAI are more likely to use increased trunk flexion during anterior reach which suggests a compensation strategy for reduced ankle control is to manipulate the pelvis and trunk. 

ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION (ACLR):

• The same authors (De la Motte, Arnold & Ross., 2015, p.358) also studied trunk movements in ACL patients and found that following an ACLR, when reaching forward, patients are more likely to rotate their trunk away (backwards) from the reach leg and externally rotate the pelvis on the stance leg. 
• In a different study following ACLR, researchers found that when looking above the ankle and at the knee, patients with reduced quadricep strength have reduced reach capacity in the anterior directions (Clagg, Daterno, Hewett & Schmitt., 2015). 
• These same authors also found that hip abductions strength impacts all 3 directions, telling us that dynamic balance has contributions from the foot, ankle, knee, hip and trunk and our assessment of movement patterns should try consider all these areas too. 

What this tells us is that people will show us their movement compensations for maintaining their centre of mass within the base of support - which will help guide treatment directions for retraining dynamic balance control. 

Another point that I have found interesting about this literature is that many studies evaluate SEBT performance 6-12 months (~6.7 months) after surgery. For me it is crucial to assess this early on, and master the dynamic balance before progressing to more dynamic or sport specific tasks. The reason I feel this test is left too late is because it is often used to determine if patient's can return to sport. It has been noted that patients who have undergone an ACLR will perform worse on both legs compared to healthy control groups and the injured leg can be up to 28% different from the unaffected side (Gribble, Hertel & Plinky., 2012 , p.349). But at the time of return to sport, we should be hoping that side to side differences don't exist. Perhaps this test needs to be incorporated earlier into our treatment plans to best help patients prepare for the next stage of their recovery?

PATELLOFEMORAL PAIN SYNDROME (PFPS):

Anterior reach involves a higher quadricep contraction, more ankle DF and greater loading on the patellofemoral joint. This reach direction is commonly the most limited in PFPS - which functionally impacts a patient’s ability to walk down slopes and stairs.

IMPLEMENTATION INTO REHAB

The video above is an example of using the SEBT to assess dynamic balance then then designing an exercise to address dynamic balance from the trunk, hip, knee, ankle etc. The one above is awesome for a top-down training approach. 

Just a few final points to consider. When going through all these studies about different body parts and patient populations what I didn't read a lot about is normative ranges for distance and cut off scores for injury risk. This again comes back to the idea that this test is multifactorial and not injury specific. It can be used to assess athletes, active individuals and occupational workers.

Please remember that dorsiflexion ROM is important to consider for it's impact on anterior reach in a single leg squat. Another consideration is not to have the expectation that all directions will be equal, as they have different functional demands.

The SEBT is amazing at exposing side to side differences and showing us how patients compensate when their balance is challenged. It can help us guide our rehab programs and focus on quality of movement. As Gribble et al (2012, p.355) worded so eloquently, “because the SEBT requires strength, flexibility, neuromusclar control, core stability, ROM, balance, and proprioception, it makes an excellent test for pre-participation physicals and clinical examinations because one faulty component is any of these systems will cause a positive test." The SEBT is a great tool which helps us tailor our rehab programs to address the specific mechanical, sensory and functional impairments. It all depends what we find during the test. 

Sian

 Sian Smale is an Australian-trained and APA-titled Musculoskeletal Physiotherapist. Sian has been writing a Physiotherapy evidence-based blog for the past 3 years called Rayner & Smale. Sian is based out of San Francisco and continues to write and teach Clinical Pilates while working towards her Californian Physical Therapy license. 

REFERENCES:

Clagg, S., Paterno, M. V., Hewett, T. E., & Schmitt, L. C. (2015). Performance on the modified star excursion balance test at the time of return to sport following anterior cruciate ligament reconstruction. journal of orthopaedic & sports physical therapy, 45(6), 444-452.

Cuğ, M. (2017). Stance foot alignment and hand positioning alter star excursion balance test scores in those with chronic ankle instability: What are we really assessing?. Physiotherapy Theory and Practice, 33(4), 316-322.

De La Motte, S., Arnold, B. L., & Ross, S. E. (2015). Trunk-rotation differences at maximal reach of the star excursion balance test in participants with chronic ankle instability. Journal of athletic training, 50(4), 358-365.

Dill, K. E., Begalle, R. L., Frank, B. S., Zinder, S. M., & Padua, D. A. (2014). Altered knee and ankle kinematics during squatting in those with limited weight-bearing–lunge ankle-dorsiflexion range of motion. Journal of athletic training, 49(6), 723-732.

Gabriner, M. L., Houston, M. N., Kirby, J. L., & Hoch, M. C. (2015). Contributing factors to star excursion balance test performance in individuals with chronic ankle instability. Gait & posture, 41(4), 912-916.

Gribble, P. A., Hertel, J., & Plisky, P. (2012). Using the Star Excursion Balance Test to assess dynamic postural-control deficits and outcomes in lower extremity injury: a literature and systematic review. Journal of athletic training, 47(3), 339-357.

Gribble, P. A., Kelly, S. E., Refshauge, K. M., & Hiller, C. E. (2013). Interrater reliability of the star excursion balance test. Journal of athletic training, 48(5), 621-626.

Hertel, J., Braham, R. A., Hale, S. A., & Olmsted-Kramer, L. C. (2006). Simplifying the star excursion balance test: analyses of subjects with and without chronic ankle instability. Journal of Orthopaedic & Sports Physical Therapy, 36(3), 131-137.

Earl, J. E., & Hertel, J. (2001). Lower-extremity muscle activation during the Star Excursion Balance Tests. Journal of Sport Rehabilitation, 10(2), 93-104.

Hyong, I. H., & Kim, J. H. (2014). Test of intrarater and interrater reliability for the star excursion balance test. Journal of physical therapy science, 26(8), 1139-1141.

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