Temporal three-dimensional spatial analysis of centre of mass during a postural balance test and effect of static taping
Background. Temporal and two-dimensional measures of reach distance and joint angles, centre of pressure and centre of mass (CoM) are common features investigated in clinical and sports settings to determine postural stability or movement variability. However, postural stability or movement variability are complex, nonlinear, multidimensional patterns requiring a 3D model of movement variability. The current study therefore applied a three-dimensional representation of changes in CoM whilst undertaking a balance test.
Methods. The box-counting fractal analysis method was applied in 3-dimensions to the $x,y,z$ data obtained during a Y-Balance Test (YBT) and the three-dimensional fractal dimension (3DFd) of CoM dispersion. Twenty participants were recruited to undertake the YBT, which required participants to stand on their dominant leg and maximally stretch the non-dominant leg in the anterior, posterolateral and posteromedial direction. CoM provides an indication of whole-body movement variability as it is based on vertical and horizontal sway. Participants were tested with and without support taping (static tape, ST) applied to the ankle, lower leg and thigh. Three-dimensional motion capture data and ground reaction forces were used to calculate CoM following kinetic and kinematic assessment of the pelvis and lower limb.
Results. Static taping significantly decreased or increased 3DFd of CoM dispersion (postural sway) compared to no taping, whilst maximum reach, a traditional two-dimensional measure, found no significant differences. Twelve participants had greater 3DFd with ST versus control $(\bar x\pm SD; 1.3\pm 0.05\, \&\, 1.26\pm 0.06; p=0.0003)$ whereas eight participants had lower 3DFd $(1.2\pm 0.05\, \&\, 1.29\pm 0.05; p=0.005)$.
Conclusion. Our results identify 3DFd as a robust method to investigate postural stability, which provides objective data on the complexity of CoM dispersion during the YBT and the effect of taping. The three-dimensional analysis provides a more complete indication of complexity compared to current two-dimensional movement variability measures, measures of movement variability should consider vertical changes in addition to horizontal sway. Future work will include a larger sample size and investigate factors that may have contributed to increased or decreased complexity and effect of taping.