BALANCE ASSESSMENT: A CRITICAL ANALYSIS

As a human being goes about their daily activities, they experience perturbations when navigating their environment. During sporting activities the magnitude of these perturbations intensifies and repeatedly occurs, making an athlete's ability to maintain balance extremely difficult. Balance is an important concept that holds immense significance not only to athletes but the practitioners that work with them, i.e. strength and conditioning coaches. It is imperative to determine which balance assessments are of the most significant benefit for strength and conditioning coaches to administer. The information collated through the assessment of balance provides insight regarding possible underlying functional impairments. Lower extremity muscular strength, ankle instability and insufficient range of motion (ROM) are all examples of possible underlying mechanisms affecting an athlete's balance. Additionally, neural impairments, such as those associated with a loss of stability as a consequence of concussion through sensory inhibition, is another example (Murray, Salvatore, & Powell, 2014).

Knowledge of existing functional impairments can aid practitioners in attempts to resolve them or prevent further decline. Deviation from a baseline test result, following a collision in a match, could help identify a concussion on the sideline. This outcome can influence return to play decisions, making balance assessment a useful athlete monitoring tool and preventative strategy. Balance assessments currently used in the athletic setting vary from static to dynamic in design; therefore, the specificity of an athletic task warrants consideration when determining a test to use. There is currently no gold-standard assessment. Consequently, understanding which tests are reliable and valid is important. The purpose of this article is to discuss balance assessment.

Balance, otherwise known as postural stability, is an individual's ability to maintain their centre of mass (COM) within their base of support (BOS). There are three neural systems involved; the somatosensory, vestibular and visual systems. These systems interact with voluntary motor control systems by sensing change and initiating a feedback response (Kreighbaum, 1996). This idea of sensory information initiating a response (action) is a perception-action couple. It is a key component of dynamical systems theory (Davids, Button, & Bennett, 2008). These concepts above are significant to balance because each holds training and movement implications, and highlights the need for balance assessments like the sensory organisation test.

           The sensory organisation test (SOT) is a well-established lab-based assessment that assesses balance on a force platform (Cripps & Livingston, 2013). During the procedure, postural stability is challenged through manipulation of sensory feedback information. Sensory feedback is controlled by the force platform, which moves in the direction of the individual's postural sway. The individual must attempt to maintain a steady, quiet stance in 6 difficult conditions (Murray et al., 2014). The test, by design, assesses neural strengths and deficits which are important because each has strength and conditioning implications. However, Cripps and Livingston (2013) state that it is an expensive, time-consuming assessment tool and is not practical to employ regularly. Murray et al. (2014) share this opinion, stating that despite displaying moderate reliability and fair validity, it is not easily accessible to the majority yet. Inaccessibility is not the only critique of this form of balance assessment. Additionally, it is not beneficial for those practitioners that are assessing balance in athletes experiencing symptoms of a concussion (Murray et al., 2014). 

           It is easy to criticise a static balance assessment like the SOT since it assesses balance from a static position. The SOT, as an example, is not conducive to the dynamic tasks athletes undertake in their chosen sports. Principle four of stability and mobility is concerned with one limb moving to compensate the motion of another, in order to keep the COM within the BOS and maintain postural stability in actions such as running. Highlighting the importance of establishing dynamic balance assessment protocols. Four key concepts underpin dynamical systems theory. The constraints-led approach is arguably the most important as it is concerned with the limits or boundaries of a system and includes organism, environmental and task constraints (Davids et al., 2008). When determining the task validity of an assessment protocol for postural stability, environmental and task constraints require consideration in order to provide a more specific test. Environmental constraints are external to the athlete such as the playing surface or the temperature, i.e. playing on an indoor court as opposed to an outdoor turf (Davids et al., 2008). Task constraints are to do with the goal of the activity, i.e. Basketball players needing to stabilise themselves as quickly as possible after landing from both contested and uncontested jumps. Wikstrom, Tillman, Smith, and Borsa (2005) state that they do not see maintaining stability on an unstable platform as an accurate representation of an athletic task. The researchers offer the dynamic postural stability index (DPSI) as a valuable means of assessment in this instance.

           Dynamic postural stability is an athlete's ability to maintain their COM within their BOS even though they are shifting from an active to an inactive state (Wikstrom et al., 2005). DPSI is a dynamic postural stability assessment whereby the athlete must execute a 2-legged jump task. During the assessment, participants must attain 50% of their maximal vertical-jump height before landing one-legged with his/her hands on hips (Wikstrom et al., 2005). DPSI offers task-specific test parameters consistent with actions seen in many explosive intermittent sports such as Basketball and Football. Research shows that DPSI displays respectable test-retest reliability making it a viable tool for assessing balance before and after a neuromuscular training intervention, for example. It is multi-purposeful in that it can include monitoring improvements during the pre-season, as well as aid return to play decisions after a rehabilitation programme (Wikstrom et al., 2005). However, like the SOT, the DPSI uses a force platform making it inaccessible to most practitioners. 

A good example of an easily available test for dynamic postural stability is the Star Excursion Balance Test (SEBT). The SEBT is accessible to use in the field (Filipa, Byrnes, Paterno, Myer, & Hewett, 2010). It is said to introduce supplementary demands, namely: ROM, lower extremity muscular strength and proprioception (Gribble & Hertel, 2003). As a result, it can highlight instability at the ankle joint, patellofemoral pain and quad-strength deficits. Gribble and Hertel (2003) found that limb length and height of an individual correlate with good performance (excursion distances) in the SEBT. During the SEBT, the participant needs to maintain a single leg stance while reaching as far as possible with the other leg in 8 directions. Suggestive that excursion distances should be normalised to allow for constant comparisons between athletes. As principle two of stability and mobility states: the broader the BOS, the more solid a body is. A bigger foot is longer than that of the smaller individual resulting in a performance advantage through greater balance in the anteroposterior direction. Subsequently, individuals with a broader foot would boast better mediolateral stability. While a strong performance in a test is not immediately transferable to athletic performance differences among taller or smaller athletes, lower extremity strength deficits hold significant training implications.

           Another essential aspect of dynamical systems theory is self-organisation (Davids et al., 2008), a theory of coordination whereby we display movement patterns that we prefer – this is known as an attractor state. For example, a lower extremity muscular strength deficit could lead to a performance decline, and the aforementioned preferred attractor state could be key. Through an effective training programme, increasing strength could lead to a self-organisation phase shift resulting in a new attractor state, thus leading to an improvement in performance (Davids et al., 2008). Gribble and Hertel (2003) and Filipa et al. (2010) state that quad strength deficits, in particular, correlate with the recovery of ACL injuries; potentially highlighting an increased injury risk. Self-organisation is, therefore, also crucial in rehabilitation and athlete monitoring.

The purpose of this article was to critically discuss a selection of balance assessments currently used in the industry. Data derived from these balance assessments provides insight into a range of impairments, both neural and physical. Each has training implications. Programming can prove to be a useful tool if created using this information. Time constraints and accessibility are important considerations when determining the best test to use. Any test administered should display test-retest reliability and be a valid means of testing balance. The SEBT test seems to be the most accessible. It can be administered on multiple occasions at a moment's notice, which could prove vital when making a return to play decision on the sideline. Lastly, the SEBT is said to be immense in the assessment of dynamic postural stability, which is more specific to many sporting tasks than static assessment. Despite that, however, more research should be done in this area to determine a gold standard for dynamic postural stability.