Reliability of independent kinetic variables and measures of inter-limb asymmetry associated with bilateral drop-landing performance

The purpose of this investigation was to establish the within-session reliability for peak vertical ground reaction force (vGRF), time to peak vGRF, and loading rate, both unilaterally and bilaterally, during a drop-landing task as well as the reliability of inter-limb asymmetry in peak vGRF. Twenty-two men (age = 22 ± 4 years; height = 180.4 ± 6.1 cm; mass = 77.9 ± 14.0 kg) and 17 women (age = 20.4 ± 3.6 years; height = 164.6 ± 9.4 cm; mass = 60.3 ± 9.8 kg) volunteered for a single testing session. Participants completed three maximum countermovement jumps (CMJ) to establish maximum jump height before performing five bilateral drop-landings from 50%, 100%, and 150% of their maximum CMJ height. The bilateral drop-landing protocol was then repeated after a 10 min recovery. Systematic bias, intraclass correlation coefficient (ICC), coefficient of variation (CV%) and minimal detectable change (MDC) values for each kinetic measurement was calculated for the left and right leg, as well as their average. There was no systematic bias present between trials (P > 0.05). All kinetic measurements showed relative reliability, ranging from large to near perfect (ICC = 0.57–0.95). Absolute reliability ranged considerably depending on the measure and drop-height, with peak vGRF and time to peak GRF showing the greatest reliability at higher drop heights (CV% = 6.6–9.7%). Loading rate for all drop heights demonstrated CV% ranging 13.0–27.6%. Furthermore, MDC values for inter-limb asymmetries in peak vGRF ranged between 14.5–16.2% for all drop heights. Overall, many of the kinetic measurements evaluated were sufficiently reliable to detect typical changes in bilateral drop-landing performance when greater drop heights were used.