Lower-limb damping characteristics during various repetitive jumping forms: Reliability and sensitivity analysis

An essential aspect of jumping performance is the ability to control impact forces. One of the key measures of this ability is the damping ratio, a dimensionless parameter that quantifies the rate at which oscillations decay following a disturbance. This study aims to assess the intra-session and inter-session reliability of damping ratios at different lower-limb anatomical landmarks and evaluate their sensitivity in detecting differences between various repetitive jumping forms, with an emphasis on establishing a specific methodological approach. Twenty-three physically active male and female students performed maximal countermovement jumps (CMJs) and bilateral (BL) and unilateral (UL) hopping (HOP). Ten wireless inertial measurement units recorded inertial data of five bilateral lower-limb anatomical landmarks. Results showed that the damping ratios during CMJ and HOPUL demonstrated good reliability, whereas in HOPBL were moderately reliable. The damping ratios of nearly all the anatomical landmarks differed between the jumping forms. CMJ had the highest values, HOPBL the lowest, and HOPUL values in between, likely due to variations in joint stiffness and amplitude displacement, as well as stretch‒shortening cycle reliance. Methodologically, using 20 repetitions in an intra-session trial and averaging left and right sides for inter-session reliability and inter-jump sensitivity, damping ratios are acceptably reliable and sufficiently sensitive for biomechanical analysis of different repetitive jumping forms. This metric could potentially be a valuable tool in developing theoretical nonlinear multibody mass‒spring‒damper models and could enhance biomechanical analysis with practical applications in sports training and rehabilitation.