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Daniel G. Miner, Brent A. Harper and Stephen M. Glass

Context: Current tools for sideline assessment of balance following a concussion may not be sufficiently sensitive to identify impairments, which may place athletes at risk for future injury. Quantitative field-expedient balance assessments are becoming increasingly accessible in sports medicine and may improve sensitivity to enable clinicians to more readily detect these subtle deficits. Objective: To determine the validity of the postural sway assessment on the Biodex BioSway™ compared with the gold standard NeuroCom Smart Equitest System. Design: Cross-sectional cohort study. Setting: Clinical research laboratory. Participants: Forty-nine healthy adults (29 females: 24.34 [2.45] y, height 163.65 [7.57] cm, mass 63.64 [7.94] kg; 20 males: 26.00 [3.70] y, height 180.11 [7.16] cm, mass 82.97 [12.78] kg). Intervention(s): The participants completed the modified clinical test of sensory interaction in balance on the Biodex BioSway™ with 2 additional conditions (head shake and firm surface; head shake and foam surface) and the Sensory Organization Test and Head Shake Sensory Organization Test on the NeuroCom Smart Equitest. Main Outcome Measures: Interclass correlation coefficient and Bland–Altman limits of agreement for Sway Index, equilibrium ratio, and area of 95% confidence ellipse. Results: Fair–good reliability (interclass correlation coefficient = .48–.65) was demonstrated for the stance conditions with eyes open on a firm surface. The Head Shake Sensory Interaction and Balance Test condition on a firm surface resulted in fair reliability (interclass correlation coefficient = .50–.59). The authors observed large ranges for limits of agreement across outcome measures, indicating that the systems should not be used interchangeably. Conclusions: The authors observed fair reliability between BioSway™ and NeuroCom, with better agreement between systems with the assessment of postural sway on firm/static surfaces. However, the agreement of these systems may improve by incorporating methods that mitigate the floor effect in an athletic population (eg, including a head shake condition). BioSway™ may provide a surrogate field-expedient measurement tool.

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Stephen M. Glass, Brian L. Cone, Christopher K. Rhea, Donna M. Duffy and Scott E. Ross

Context: Previous work suggests that balance behavior is a sex-dependent, complex process that can be characterized by linear and nonlinear metrics. Although a certain degree of center of pressure variability may be expected based on sexual dimorphism, there is evidence to suggest that these effects are obscured by potential interactions between sex and anthropometric factors. To date, no study has accounted for such interactive effects using both linear and nonlinear measures. Objective: This investigation sought to analyze interactive models featuring sex, height, and weight as predictors of linear and nonlinear aspects of postural control. Design: Cross-sectional study. Setting: Controlled laboratory. Participants: A total of 26 males (23.80 [3.44] y, 177.87 [6.44] cm, 81.70 [10.80] kg) and 28 females (21.14 [2.03] y, 169.57 [8.80] cm, 64.48 [8.86] kg) were sampled from a healthy university population. MainOutcomeMeasures: Linear (range [RNG], velocity [VEL], and SD) and nonlinear (detrended fluctuation analysis scaling exponent, multivariate multiscale sample entropy [MMSECI]) summary metrics of center of pressure time series. Procedure: Participants stood on a force plate for 20 seconds in 3 conditions: double (D), single (S), and tandem (T) stance. Data for each stance condition were analyzed using regression models with interaction terms for sex × height and sex × weight. In D, weight had a positive, significant main effect on VELy, MMSECId, and MMSECIv. In men, height was observed to have a positive effect on SDy (S), RNGy (S), and RNGx (T) and a negative effect on MMSECIv (T). In women, weight was observed to have a positive effect on SDy and VELx (both T). Conclusions: Our findings suggest that men and women differ with respect to certain linear and nonlinear aspects of balance behavior, and that these differences may reflect sex-specific behavioral patterns in addition to effects related to sexual dimorphism.

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Stephen M. Glass, Alessandro Napoli, Elizabeth D. Thompson, Iyad Obeid and Carole A. Tucker

The balance error scoring system (BESS) is a human-scored, field-based balance test used in cases of suspected concussion. Recently developed instrumented alternatives to human scoring carry substantial advantages over traditional testing, but thus far report relatively abstract outcomes that may not be useful to clinicians or coaches. In contrast, the automated assessment of postural stability (AAPS) is a computerized system that tabulates error events in accordance with the original description of the BESS. This study compared AAPS and human-based BESS scores. A total of 25 healthy adults performed the modified BESS. Tests were scored twice each by 3 human raters and the computerized system. Interrater (between human) and intermethod (AAPS vs human) agreement (interclass correlation coefficient2,1) were calculated alongside Bland–Altman limits of agreement. Interrater analyses were significant (P < .01) and demonstrated good to excellent agreement. Intermethod agreement analyses were significant (P < .01), with agreement ranging from poor to excellent. Computerized scores were equivalent across rating occasions. Limits of agreement ranges for AAPS versus the human average exceeded the average limits of agreement ranges between human raters. Coaches and clinicians may consider a system such as AAPS to automate balance testing while maintaining the familiarity of human-based scoring, although scores should not yet be considered interchangeable with those of a human rater.

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Stephen M. Glass, Christopher K. Rhea, Matthew W. Wittstein, Scott E. Ross, John P. Florian and F.J. Haran

Transitioning between different sensory environments is known to affect sensorimotor function and postural control. Water immersion presents a novel environmental stimulus common to many professional and recreational pursuits, but is not well-studied with regard to its sensorimotor effects upon transitioning back to land. The authors investigated the effects of long-duration water immersion on terrestrial postural control outcomes in veteran divers. Eleven healthy men completed a 6-hour thermoneutral pool dive (4.57 m) breathing diver air. Center of pressure was observed before and 15 minutes after the dive under 4 conditions: (1) eyes open/stable surface (Open-Stable); (2) eyes open/foam surface (Open-Foam); (3) eyes closed/stable surface (Closed-Stable); and (4) eyes closed/foam surface (Closed-Foam). Postdive decreases in postural sway were observed in all testing conditions except for Open-Stable. The specific pattern of center of pressure changes in the postdive window is consistent with (1) a stiffening/overregulation of the ankle strategy during Open-Foam, Closed-Stable, and Closed-Foam or (2) acute upweighting of vestibular input along with downweighting of somatosensory, proprioceptive, and visual inputs. Thus, our findings suggest that postimmersion decreases in postural sway may have been driven by changes in weighting of sensory inputs and associated changes in balance strategy following adaptation to the aquatic environment.