DOES THE METHOD OF MEASURING CENTRE OF MASS DISPLACEMENT AFFECT VERTICAL STIFFNESS CALCULATION IN SINGLE-LEG HOPPING?

Abstract

The purpose of this study was to compare vertical stiffness values calculated from two kinetic and two kinematic estimations of the vertical displacement of the centre of mass. Twenty recreationally active male and female participants completed one 15 s single-leg hopping trial at 2.2 Hz with vertical stiffness calculated for the first 10 complete hop cycles. Vertical displacement was estimated using double integration (DI), first principle (FP), sacral marker cluster (SMC) and segmental analysis (SA) methods. Bland-Altman plots demonstrated the SA and DI methods to have a small bias (0.92 kN/m) and tight 95% limits of agreement (-1.16 to 3.08 kN/m). In contrast, the SMC and FP methods underestimated and overestimated vertical stiffness, respectively. These findings suggest the SA and DI methods can be used interchangeably to calculate vertical stiffness.