Validity of an Inertial Measurement Unit System to Assess Lower-limb Kinematics during a Maximal Linear Deceleration

This study examined the validity of an inertial measurement unit system for measuring lower-26 limb joint kinematics during linear decelerations. A male team athlete (age 36 years, stature 27 1.75 m, mass 80.0 kg) performed multiple linear decelerations, following 20 m runs at 50%, 28 75% and 100% self-perceived effort. Inertial measurement unit sensors were strapped to 29 lower-limb segments and retroreflective markers were adhered to the lower-limbs for 3D 30 optical motion analysis. Ground contact time, foot to centre of mass displacement (foot-31 COM), peak and minimum angle, mean angular velocity and range of motion at the ankle, 32 knee and hip during the contact phases of each deceleration were determined. Measures were 33 valid if a very large correlation (r ≥ 0.7) and small bias (effect size < 0.6) were evident. 34 Following 50% effort, ground contact time, foot-COM and most hip and knee kinematics 35 were valid. Ground contact time, foot-COM and knee flexion velocity and range of motion 36 were valid following 75% efforts. Ground contact time and knee flexion velocity were valid 37 following 100% effort. Therefore, the inertial measurement unit system tested can be used to 38 assess temporal-spatial parameters during a deceleration regardless of the preceding effort, 39 and hip and knee kinematics following low intensity running.