Original researchBetween-session reliability of the star excursion balance test
Introduction
Dynamic postural control is described as the ability to maintain a stable base of support whilst completing a prescribed movement (Winter, Patla, & Frank, 1990) and underpins the performance of movement skills in the athletic population. The Star Excursion Balance Test (SEBT) has been reported to assess dynamic balance and challenge athletes sufficiently (Hertel et al., 2000, Kinzey and Armstrong, 1998). The SEBT has been widely used in research and clinical practice to examine numerous topics, such as chronic ankle instability (CAI) (Gribble et al., 2004, Hertel et al., 2006, Olmsted et al., 2002), anterior cruciate ligament (ACL) injury (Herrington, Hatcher, Hatcher, & McNicholas, 2009), injury prediction (Plisky, Rauh, Kaminski, & Underwood, 2006) and the effect of patellar taping (Aminaka & Gribble, 2008). The SEBT offers a simple, low-cost alternative to more sophisticated laboratory assessments for use in clinical settings.
The SEBT involves participants carrying out a number of reaching tasks with one limb whilst maintaining balance on the other (Hertel et al., 2000). The SEBT is a closed-kinetic chain exercise which mimics the single-leg squat exercise and therefore the stance leg requires strength, proprioception, neuromuscular control and adequate range of motion at the hip, knee and ankle joints (Olmsted et al., 2002).
One problem which has been associated with the SEBT is the time-consuming protocol. This protocol involves participants performing 6 practice trials in each direction before undertaking a further 3 measured trials and is based on the results of Hertel et al. (Hertel et al., 2000). Hertel and colleagues suggested this number of practice trials were necessary as they found significant learning effects occurred across trials 1 to 6 during testing, with scores stabilising and longest excursion distance occurring from trials 7 onwards. This was further reflected in higher reliability scores for trials 7 to 12 compared to trials 1 through 6. However, the authors administered the 12 trials in 4 blocks on 2 separate days, which may have affected performance between trials. Participants were also allowed to use their arms freely, which does not reflect the most commonly used SEBT protocol of hands remaining on hips. Both of these factors may increase the amount of time needed to learn the task (Robinson & Gribble, 2008).
Considering this Robinson and Gribble (Robinson & Gribble, 2008) studied maximum normalised excursion distances in order to determine how many trials are needed for scores to stabilise. Participants performed the recommended protocol of 6 practice and 3 test trials in all 8 reach directions (Hertel et al., 2000). The results showed that only the lateral reach direction needed more than 4 practice trials before stability was achieved, and in that case it was achieved on the fifth trial. The authors concluded that the number of practice trials needed could be reduced from 6 to 4, therefore streamlining the SEBT protocol. Combined with previous findings which support the reduction of reach directions needed for certain injuries, SEBT administration could be greatly simplified, with fewer practice trials and fewer reach directions tested. However, further research and justification is needed in this area.
High inter-tester reliability of the SEBT has previously been reported (Hertel et al., 2000). Whilst previous studies have evaluated intra-tester reliability (Hertel et al., 2000, Kinzey and Armstrong, 1998), only one study has evaluated between-session reliability of the SEBT with normalised scores, with ICC values ranging from 0.89 to 0.93 (Plisky et al., 2006). However, only 3 reach distances; anterior, postero-medial and postero-lateral were evaluated. Therefore, further study of between-session reliability of all reach directions is warranted.
Perhaps most importantly, to date no study has looked at measurement error associated with the SEBT and what percentage change reflects a true improvement in performance. This information is important to evaluate previous and future research, especially intervention studies, and also for practitioners who use the SEBT to evaluate individual performance during training or rehabilitation. Without measurement error values, changes in performance cannot be evaluated properly as it is not known whether these changes may be attributed to measurement errors or from the intervention.
Therefore the aims of the current study are firstly, to re-visit the learning effects associated with the administration of the SEBT to determine how many practice trials are needed before scores stabilise; secondly, to establish the between-session reliability using a standardised protocol; and finally to ascertain error scores in order for true changes in performance to be identified.
Section snippets
Participants
Twenty-two participants (11 female; age 22.3 ± 3.7 years, height 167.7 ± 6.2 cm, weight 59.2 ± 6.9 kg and 11 male; age 22.8 ± 3.1 years, height 179.8 ± 4 cm, weight 79.6 ± 10 kg) all of whom were university students volunteered for the study. Participants were required to be free from lower extremity injury for at least 6 months prior to testing, have no history of hip, knee or ankle surgery and participate in a minimum of 30 min of physical activity three times a week. All subjects signed an
Results
Independent t-tests revealed no significant differences between males and females or between dominant and non-dominant limbs for all reach directions (p > 0.05); therefore they were grouped for all further analysis, giving an overall number of 44 limbs. Table 1 shows the mean and standard deviations for normalised maximum excursion distances and indicates where significant differences between trials were found. All directions except posterior–lateral showed a significant increase (p < 0.05) in
Discussion
The findings of this study support those of Robinson and Gribble (Robinson & Gribble, 2008) who found that maximum normalised excursion distance scores stabilise after four practice trials and therefore SEBT administration could be simplified from performing six practice trials as previously recommended (Hertel et al., 2000). Hence, a standardised protocol of 4 practice trials followed by 3 measured trials should be adopted for use in clinical practice and further research.
Having established
Ethical approval
All participants gave written informed consent to participate and the research was approved by the University of Salford Research and Ethics Committee.
Funding
No funding was received for completion of this study.
Conflict of interest
No conflicts of interest were present in this study.
Acknowledgements
I affirm that I have no financial affiliation or involvement with any commercial organisation that has a direct financial interest in any matter included in this manuscript.
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