# Wobble Board Performance: A Practical and Useful Quantification in Balance Assessment
###### Abstract  
Balance is integral in ankle injury prevention and therapy, especially in high-risk sports like volleyball. For balance assessment, the recommended wobble board (WB) performance (i.e., time at equilibrium) has never been compared with the gold standard. The objective was to investigate the relationships of force-plate-derived center of pressure (CoP) with WB performance and the accuracy of WB-derived CoP estimates. Twelve high-level volleyball players completed six unipedal standing trials on a computerized WB. WB tilt angles and CoP were obtained simultaneously via tri-axis accelerometers on the WB (200 Hz) and a force plate (1000 Hz), respectively. WB performance, polynomial-transformed CoP estimates, and CoP fractal sway, sway area, and mean sway velocity were assessed via Pearson and concordance correlation, root mean square errors, and dependent \(t\)-tests. WB performance was related with CoP sway and sway area (1t\({}_{\text{linear}}\)! = 0.714-0.842, 1r\({}_{\text{nonlinear}}\)! = 0.833-0.910, \(p\)! = 0.01). The strongest concordance (0.878-0.893, \(p\)! 0.001) and smallest errors (6.5-10.7%) were reported for anterior-posterior sway and sway area. Moderate to excellent relationships between the WB performance and force plate CoP variables supported the usefulness of WB performance and estimates (especially sway area) in balance assessment. Furthermore, this study presents recommendations for future analyses and modeling approaches to reflect the complexity of postural control. biomechanics; assessment; kinetics; measurement; testing +
Footnote †: journal: _Sci_  
0000-0001-9993-3000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-0000-00000-00000-00000-00000-00000-00000-00  
of ankle functionality to maintain balance, individuals with ankle injuries often exhibit balance deficits, leading to increased risk of reinjury [9]. Sports like volleyball, notorious for ankle injuries especially among high-level competitors [10], necessitate specific injury prevention programs such as balance training [10]. For the effective monitoring and assessment of training outcomes, reliable and valid methods of balance testing are indispensable [3]. Balance tests can also detect pathologies that are associated with balance [5; 11; 12]. Timed unipedal stance tests yielded high reliability and were recommended as a suitable task for balance assessment [5]. Among various methodologies and devices (e.g., force plates, accelerometers, and functional tests), force plates and specifically the measurement of the center of pressure (CoP) sway are considered as the gold standard for balance assessment [13; 14]. However, the costs, weight, and complexity in data processing limit the application of force plates in large-scale and in-field testing [5; 15]. Therefore, alternative devices and practical protocols have been recommended [5; 16], e.g., computerized wobble boards (WBs) [17; 18]. Cheap and mobile in comparison with force plates, WBs are unstable platforms frequently used to train balance control [1; 2; 19]. When instrumented with accelerometers or gyroscope sensors, WBs can also be used for balance assessment [17; 20; 21]. Such instrumented WBs can obtain the tilt angle of the board during balance tasks. The change in the tilt angle over time mirrors CoP sway, with smaller tilt angles indicating better postural control. One study compared the WB tilt angle derived from an inertia measurement unit with the angle derived from a Vicon motion capture system [22]. The authors reported great concurrent validity for the WB to measure tilt angles (R\({}^{2}\) > 0.99) [22]. When comparing WB tilt angles with force-plate-derived CoP, however, findings have been controversial [23; 24]. One study reported correlation coefficients of \(-\)0.14-0.30 between WB tilt angle excursion and force plate CoP velocity in the sagittal and frontal plane separately [23]. Nevertheless, WB-derived CoP path length was able to reflect impaired balance in men with Achilles tendinopathy [25].