Normative Data for the BTrackS Balance Test Concussion-Management Tool: Results From 10 045 Athletes Aged 8 to 21 Years

Millions of concussions are sustained each year by children, adolescents, and adults while playing sports.¹ These mild traumatic brain injuries are complex due to multiple neurologic and biomechanical factors.² Not surprisingly, concussions have wide-ranging symptoms that include both psychosomatic variables (eg, nausea, blurred vision, loss of consciousness) and cognitive and motor deficits.³

To manage sport-related concussion, the most recent consensus statement by the Concussion in Sport Group⁴ advocated balance testing as one component. This recommendation is supported by studies^5–9 that showed many concussed athletes had worse balance than at preseason baseline testing.

The BTrackS Balance Test (BBT; Balance Tracking Systems, Inc, San Diego, CA) was 90% specific and 64% sensitive in identifying individuals with sport-related concussion.⁹

The BBT is a concussion-management tool that uses low-cost force-plate technology to objectively measure postural sway (ie, balance). Postural sway is classically defined as sustained oscillatory motion about a fixed postural position during upright standing.¹⁰ Force plates determine postural sway based on a proxy for the body's center of mass called center of pressure (COP). Center of pressure is equal to the weighted average of forces created when an individual stands on a force plate. Increased COP magnitude over time indicates more postural sway and poorer balance.¹¹

The best practice for concussion management typically involves comparing postconcussion test results with results obtained at baseline.¹² Despite this, normative databases are valuable for further contextualizing performance. For example, it is rarely possible to gather baseline data from all athletes in larger academic settings due to time and manpower constraints. In this case, the ability to compare postconcussion results with age- and sex-matched norms can significantly improve the ability to interpret results. Second, athletes may occasionally malinger, or intentionally underperform, on baseline tests to increase the likelihood of later passing a postconcussion test. Using normative data at baseline can reduce this unwanted practice by alerting sports medicine professionals to suspicious results at the time of testing. Alternatively, low baseline test results compared with norms may not reflect malingering but rather latent neuromuscular concerns from previous concussions or musculoskeletal injuries.

The purpose of our study was to provide athlete-specific normative data for the BBT. We accomplished this by calculating percentile rankings for the baseline BBT results of athletes aged 8 to 21 years using 1 of the largest balance datasets of postural sway collected (n = 10 045). In line with previous authors,^13–20 we hypothesized that older athletes would perform better (ie, have less postural sway) than younger athletes and that females would outperform males. Our goal was to enhance the efficacy of BBT testing and the management of patients with sport-related concussion.

METHODS

Experimental Setup

The assessments of postural sway were conducted at each testing site using a BTrackS Balance Plate and BTrackS Sport Balance software (version 4; Balance Tracking Systems, Inc; Figure 1). The BTrackS Balance Plate is a low-cost (<$1000, no per-test fees), Food and Drug Administration-registered, and portable (<7 kg) force plate used to measure COP. Validity of the BTrackS Balance Plate has been established against several other accepted methods of COP measurement. Specifically, BTrackS has shown excellent accuracy (intraclass correlation coefficient [ICC] = 0.999), precision (ICC = 0.999), and reliability (ICC = 0.999) against a laboratory-grade force plate and a computer numerical control-administered point-of-application test.^21,22 The BTrackS Sport Balance is a user-friendly software application for conducting the BBT. This software was run on computing devices (personal computers, laptops, or tablets) using full versions of the Windows operating system (Microsoft Corp, Redmond, WA).

View Figure

• Download as Powerpoint
• Download Figure

RESULTS

Based on the analysis of variance, BBT results were affected by athlete sex (F_1,10031 = 93.8, P < .001), age (F_6,10031 = 334.3, P < .001), and a sex × age interaction (F_6,100.1 = 2.2, P = .04; Figure 2). With regard to sex, females had better BBT results (ie, less postural sway) than males in all age groups (P < .05) except 12–13 years (P > .05). For male athletes only, BBT results demonstrated less postural sway as age increased from 8–9 to 18–19 years (P < .05), with no differences between male athletes 18–19 and 20–21 years (P > .05). For female athletes only, age did not affect the BBT (P > .05) across the 2 youngest age groups (ie, 8–9 versus 10–11 years) and the 3 oldest age groups (ie, 16–17 versus 18–19 versus 20–21 years). In contrast, female athletes aged 10–11 to 12–13 years, 12–13 to 14–15 years, and 14–15 to 16–17 years had better BBT results (ie, less postural sway; P < .05).

View Figure

• Download as Powerpoint
• Download Figure

Given these sex and age effects, we determined that percentile rankings for this dataset should be stratified by both factors. Percentile ranking information by age group is provided for males (Table 1) and females (Table 2). These tables serve as tools for understanding the performance of an individual relative to others of similar sex and age. For example, a 15-year-old male with a BBT of 27 is in the 40th percentile. This means that his BBT result is as good as or better than 40% of males his age.

Table 1 The BTrackS Balance Test Percentile Rankings for Male Athletes by Age Group

View Fullscreen

Table 2 The BTrackS Balance Test Percentile Rankings for Female Athletes by Age Group

View Fullscreen

DISCUSSION

In this study, we sought to provide normative data for the BBT, a balance test of postural sway for concussion management that uses a portable, low-cost force plate. Specifically, we analyzed baseline BBT results of more than 10 000 athletes 8 to 21 years of age and provided percentile rankings based on sex and age differences. These normative results provide additional insight into an athlete's balance status when baseline BBT results are not available for comparison with postconcussion testing. Further, normative BBT data can assist in identifying athletes suspected of malingering during baseline tests and those who are experiencing a latent neurologic or musculoskeletal injury.

Across the various age groups tested, we found clear differences in BBT results for male and female athletes. These results were generally well aligned with a relatively large body of literature^16–20 that has demonstrated a reduction in postural sway with increasing age. The mechanism of this balance improvement is most likely developmental, with maturation of the brain and sensorimotor systems occurring from childhood through early adulthood.^25–27 Interestingly, improvements in postural sway in our study were seen until age 18 to 19 years in males and 17 to 18 years in females. These results are in contrast to previous findings^17–19 that suggested adult-like postural-sway control was achieved by age 14 or younger. This discrepancy in results is probably due to the large sample size in our study and the subsequent increased statistical power for determining age differences. Indeed, other recent investigators¹⁶ studying a large sample (n = 889) of athletes' force-plate data also noted improvements in postural sway up to 18 years of age.

The BTrackS Balance Test results in our research were also in general agreement with previous literature^16–20 demonstrating enhanced balance ability (ie, less postural sway) in females compared with males. The exact mechanism underlying this sex difference in postural sway remains elusive. Although it is tempting to attribute this finding to known anthropometric differences between male and female athletes, most authors^16,18–20 did not observe relationships between measures of height or weight and postural sway. To this extent, an alternative explanation may lie in a study²⁸ that showed females outperformed males on tests of vibrotactile foot sensitivity and that increased sensitivity was associated with enhanced performance on various tests of postural sway.

Several limitations are worth noting in relation to our results. First, the data were collected at multiple sites with limited oversight by us. This approach has the potential to affect internal testing validity due to site-specific differences in the testing environment and how the test was implemented. Some variation in results was also likely due to the individual(s) administering the test, although procedures were standardized and a medical device was used to objectively measure postural sway. For reasons of user privacy, the data in this study were not linked to the collection site and, therefore, no assessment of these factors was possible. However, a previous study¹⁴ involving more subjective clinical assessments showed no effects related to testing athletes' balance at multiple locations.

In addition, the sample size reflected an imbalance across the sex and age groups. At least 100 individuals were tested from each sex and age group to permit a true percentile ranking, yet some groups were overrepresented with more than 1000 athletes. Similarly, we made no attempt to provide normative data by sport due to insufficient sample sizes for most sports in the database. In future work, we hope to increase the number of athletes in smaller sex, age, and sport groupings.

Our study has clinical relevance, given that the BTrackS is a tool that can be used for concussion balance testing with evidence of diagnostic efficacy⁹ and resistance to fatigue²⁹ and practice³⁰ effects, limitations that have been associated with other concussion balance-testing tools. The existing BTrackS Sport Balance software (version 4) has normative data integrated into its analytics based on larger age groupings than those used in our study (ie, 5–9, 10–14, 15–19, and 20–29 years). Efforts should be made to incorporate our work into the next generation of BTrackS Sport Balance software to further enhance its efficacy in the field for sport medicine professionals.