Most, but not all, concussed athletes have significant balance problems (what doctors call "postural instability"), which worsen for several days after concussion but usually clear up after 3 days in high school and collegiate athletes. [1,2]
Useful test for concussion
Balance testing is considered by the 4th Consensus Statement on Concussion in Sport  ("Zurich consensus statement") to be a "useful tool for objectively assessing" neurological functioning and a "reliable and valid addition to the assessment of athletes suffering from concussion, particularly where symptoms or signs indicate a balance component." An accompanying review of the peer-reviewed medical literature  found that "the studies show that balance is an important component of the sideline assessment."
The most commonly used low-technology balance assessment for those with sports-related concussion is the Balance Error Scoring System (BESS). [3,4,15]The BESS consists of 3 tests lasting 20 seconds each, performed on a firm surface (grass, turf, court) and a piece of medium-density foam, all with the eyes closed, and scored based on the number of errors across trials:
- The athlete first stands with the feet narrowly together, the hands on the hips, and the eyes closed (double leg stance). The athlete holds this stance for 20 seconds while the number of balance errors (opening the eyes, hands coming off hips, a step, stumble or fall, moving the hips more than 30 degrees, lifting the forefoot or heel, or remaining out of testing position for more than 5 seconds) are recorded as errors.
- The test is then repeated with a single-leg stance using the non-dominant foot, and
- A third time using a heel-toe stance with the non-dominant foot in the rear (tandem stance). (A 2013 study  found that these stances were best at separating the healthy participants from the concussed patients.)
The advantages of the BESS are that it is inexpensive (the only equipment needed is a piece of foam, which can easily be carried in a travel trunk or equipment bag for road games), easy-to-administer, and quick (5-7 minutes).
Viewed as reliable
The new American Academy of Neurology concussion guidelines  view the BESS assessment tool as likely to identify concussion with only low to moderate diagnostic accuracy with a low specificity of 34 to 64% (meaning a false positive rate for concussion of 34 to 64%), but a high degree of specificity of 91% (meaning that the test will only miss one out of ten concussions).
A recent study  likewise concluded that the BESS is a useful test for assessing balance in high school-aged athletes, finding that a total BESS score of 21 or more errors optimally identified patients in the acute concussion group versus healthy participants with 60% sensitivity and 82% specificity. It also reported that the BESS could discriminate between healthy and concussed high school-aged persons beyond 3 days, at odds with an earlier study,  which found that the BESS returned to baseline 3 days after concussion.
Wait to perform
On the basis of studies showing the BESS to have a practice effect, and also that it seems to be affected not only by the environment in which the test is conducted but also by how soon after exercise the test is given, the American Academy of Pediatrics' statement on concussions recommends  that the post-concussion balance testing not be performed on a noisy sports sideline, but be delayed until 15 minutes after cessation of exercise and in a setting in which follow-up assessments can be performed. A recent literature review  also noted that BESS performance is affected by exertion and fatigue, the type of sport played, and a history of ankle injury or instability.
Best used when have baseline
Experts, including William P. Meehan, III, MD, Director of the Sports Medicine Clinic at Children's Hospital Boston and a MomsTeam concussion expert featured in MomsTEAM's new high school football concussion documentary, "The Smartest Team, believe that the BESS is best used where a baseline BESS score is obtained prior to the start of the season, when an athlete is healthy. Then, repeated scores after concussion can be used to monitor recovery.
In his 2012 book, Concussions and Our Kids  Robert Cantu, M.D., one of the country's leading concussion experts, agrees. He recommends expanding baseline testing (which most think of solely in terms of computerized neurocognitive testing, and which is routinely performed at the professional and college level and, increasingly, at the high school level, be expanded to include a balance assessment.
A modified BESS (M-BESS) performed only a firm surface is included as part of the updated Sports Concussion Assessment Tool (SCAT3) issued in conjunction with the Zurich Consensus Statement. The 2013 American Medical Society for Sports Medicine position statement on concussions,  however, expressed skepticism about the M-BESS, noting that it was not supported by any reliability studies, that no clinically meaningful change in the error rate had been established, and that its sensitivity and specificity (the percentage of concussed athletes correctly identified by the test, and the proportion of non-concussed athletes correctly identified as not having a concussion, respectively) had not yet been established. That criticism appeared prescient, as a 2013 study  found that the M-BESS included in the SCAT-2/3 did not discriminate between concussed athletes and healthy controls, casting significant doubt on its utility.
The AMSSM also raised practical issues with using the BESS in a sideline setting: "Baseline testing is typically done in a training room on a firm surface in sneakers without tape, or ankle braces. Sideline testing is typically done in cleats with ankles taped or braced on a grass or turf field." It neverthless stated that, "despite these limitations, balance is often affected by concussion and should be evaluated where a concussion is suspected." Ideally, says the AMSSM, the baseline M-BESS should be done in 'game' conditions, and it called for more research to refine sideline balance testing.
High-tech and intermediate tech balance assessment tools
The most common high-technology balance assessment is the Sensory Organization Test (SOT), which uses computerized dynamic posturography to measure how much a person sways when standing in certain positions on a force plate. Studies using the SOT have shown that patients with sports concussions tend to sway more than healthy persons 1 day after injury. Using this sophisticated test, measurable balance problems have been shown to last up to 30 days after a concussion, in contrast to the 3 days reported using the BESS.
While high-technology methods typically provide greater sensitivity, precision and reliability, especially at longer intervals after injury, the machines, and the accompanying computer software, are expensive and are often cost-prohibitive for smaller, less well-funded athletic programs.
An intermediate technology thought to have promise in assessing balance is the Balance Accelerometer Measure (BAM), which employs a small wearable sensor that allows balance testing outside a clinic based on an objective sensor signal. Although not specifically designed to assess patients with concussions, the BAM can be used with persons of any age and can be administered safely with little training.
However, a 2013 study  evaluating the ability of the BAM and the BESS to assess postural control in distinguishing between high school students at various time points after a concussion compared with healthy controls reported that the BAM was unable to discriminate between healthy and concussed adolescents, prompting researchers at the University of Pittsburgh Medical Center to conclude that the "BAM did not appear to be useful for assessing balance problems after concussions in this age group." (By contrast, the BESS, especially the tandem stance conditions, was found to be good at identifying abnormal postural control in adolescents with sports concussion)
While reliable alternatives to the BESS may become available (including the Wii Fit video game player) to assess balance, Dr. Meehan, for one, views the BESS as "the most thoroughly studied, most easily understood, and most readily available for use in managing sport-related concussions." 
Poor balance and dizziness are different
Balance problems are often linked to dizziness as objective and subjective impairments of similar nervous system functioning, but they are distinct albeit overlapping conditions. Concussions can cause balance problems by adversely affecting either the central nervous system or the inner ear balance mechanism. Dizziness can be the result of a variety of organic reasons, including disturbances in vestibular (ie. vertigo), visual, or cardiovascular (ie. fainting) systems.
While postural stability and balance can be tested objectively using such tests as the Romberg, tandem walking, heel-to-toe, BESS, Clinical Test of Sensory Interaction and Balance (CTSIB), and biomechanical force-plate tests, there is no consensus measure for dizziness, which is typically measured using postural/balance testing, self-report dizziness questionnaires, or both.
A 2011 study  found that dizziness, but not imbalance, was a risk factor for protracted recovery from concussion. The finding prompted the authors, researchers at the University of Pittsburgh, to suggest that postural/balance testing and dizziness tests should be looked at individually, that postural/balance testing should not be used as a proxy for dizziness, and that clincians should use dizziness questionnaires to augment post-concussion assessment in addition to computerized neurocognitive tests (e.g. ImPACT), symptom reports, and postural/balance tests.
A more recent study,  however, found no link between dizziness and prolonged recovery.
The two most recent comprehensive studies of concussions in high school athletics [12, 13] found that dizziness (74.6% and 75.6%) was the second-most reported concussion symptom behind only headaches (93.4% and 94.2%).
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