Step-to-Step Kinematic Validation between an Inertial Measurement Unit (IMU) 3D System, a Combined Laser+IMU System and Force Plates during a 50 M Sprint in a Cohort of Sprinters

Abstract

The purpose was to compare step-by-step kinematics measured using force plates (criterion), an IMU only and a combined laser IMU system in well-trained sprinters. Fourteen male experienced sprinters performed a 50-m sprint. Step-by-step kinematics were measured by 50 force plates and compared with an IMU-3D motion capture system and a combined laser+IMU system attached to each foot. Results showed that step kinematics (step velocity, length, contact and flight times) were different when measured with the IMU-3D system, compared with force plates, while the laser+IMU system, showed in general the same kinematics as measured with force plates without a systematic bias. Based upon the findings it can be concluded that the laser+IMU system is as accurate in measuring step-by-step kinematics as the force plate system. At the moment, the IMU-3D system is only accurate in measuring stride patterns (temporal parameters); it is not accurate enough to measure step lengths (spatial) and velocities due to the inaccuracies in step length, especially at high velocities. It is suggested that this laser+IMU system is valid and accurate, which can be used easily in training and competition to obtain step-by step kinematics and give direct feedback of this information during training and competition.

Keywords: force plates; inertial sensors; musclelab; xsens.

Figure 1

A typical example of five steps of the raw plantar flexion pattern measured with an IMU (Xsens system) attached on the left and right foot with corresponding contact and flight time phases.

Figure 2

Mean (±SD) step-by-step velocity averaged over all participants during 50 m sprints measured with force plates, laser+IMU and IMU-3D based systems. † indicates a significant difference for each step for this condition with the force plate condition on a p < 0.05 level. ‡ indicates a significant difference for this step for laser+IMU system with the force plate condition on a p < 0.05 level.

Figure 3

Mean (±SD) step-by-step step length, frequency, contact and flight time averaged over all participants during 50 m sprints measured with force plates, laser+IMU and IMU-3D based systems. † indicates a significant difference for each step for this condition with the force plate condition on a p < 0.05 level. * indicates a significant difference between the IMU-3D system with the force plate system for this step on a p < 0.05 level.

Figure 4

Bland-Altman plots and linear correlations between force plate, laser+IMU and IMU-3D systems for each kinematics parameter. Dashed lines indicate a systematic bias between the measuring devices (positive values mean higher values obtained with the IMU systems than force plates). The grey lines represent 95% confidence intervals.