How reliable are lower limb biomechanical variables during running and cutting tasks

The purpose of this study was to compare the within- and between-days reliability of lower limb biomechanical variables collected during running and cutting tasks. Methods: 15 recreational athletes, 7 males and 8 females, took part in three testing sessions, two sessions on the same day with an hour gap and another session one week later. Kinematic and kinetic data during running and 90° side step cutting tasks gathered using a ten-camera motion analysis system (Qualisys) and a force platform (AMTI) embedded into the floor. Results: During both tasks, within-day ICC values for joint angles (ICCrun = 0.63–0.94 and ICCcut = 0.63–0.96) were higher than between days (ICCrun = 0.51–0.72 and ICCcut = 0.42–0.83). Out of five moments tested in each task, within-day ICC values (ICCrun = 0.64–0.89 and ICCcut = 0.79–0.94) were higher than between days (ICCrun = 0.58–0.91 and ICCcut = 0.83–0.92). During running task, within and between-day SEM values for joint moments ranged between (0.07–0.39 N m kg) and between (0.98°–5.14°) for joint angles. While during cutting, SEM values for moments ranged between (0.13–0.56 N m kg) and between (1.73–5.15) for joint angle measurement. The GRF data, in both tasks, were more reliable (ICCrun ⩾ 0.84 and ICCcut ⩾ 0.88) as compared to angles (ICCrun ⩾ 0.51 and ICCcut ⩾ 0.42), and moments (ICCrun ⩾ 0.58 and ICCcut ⩾ 0.79) data. These findings are relevant to those undertaking intervention studies because of the potential for large measurement variability when examining certain variables, which would then require considerable changes in these variables to show “real” effects of the interventions beyond measurement error.