Validity Of Inertial Measurement Unit Research Articles

Use of inertial measurement units for measuring torso and pelvis orientation, and shoulder–pelvis separation angle in the discus throw

Wearable technologies, such as inertial measurement units, are being increasingly utilised in sport to provide immediate feedback to athletes and coaches on movement dynamics. This study examines the validity of inertial measurement units for measuring data pertinent to discus throwing namely shoulder–pelvis separation angle, and torso and pelvis transverse plane orientation. Five discus throwers performed 10 throws, while shoulder–pelvis separation angle, and torso and pelvis transverse plane orientation were measured simultaneously using a motion capture system and inertial measurement unit system. Time-series torso and pelvis orientation data were compared to determine the validity of the inertial measurement unit system for measuring the segment orientation. Discrete shoulder–pelvis separation angle data were compared to determine the validity of the inertial measurement unit system for measuring the discrete data pertinent to discus throwers and coaches. Discrete data examined were magnitudes of separation that occurred when the torso was maximally rotated to the left and right. Data were compared using root mean square difference and root mean square relative to angle range (RMS%). Bland–Altman analyses were also performed. Torso (RMS% = 3%) and pelvis (RMS% = 2%) orientation data agreed closely. Agreement was lower for separation angle (maximum left rotation RMS% = 9%; maximum right rotation RMS% = 13%). Bland–Altman biases indicate inertial measurement units underestimated segment orientation, underestimated maximum right rotation, and overestimated maximum left rotation. The protocol described was valid for measuring the torso and pelvis orientation. Separation angle validity was low, indicating differences in underlying modelling approaches. Further investigation is needed to examine more optimal sensor positioning, and novel ways of examining shoulder–pelvis dynamics.

Player Monitoring in Indoor Team Sports: Concurrent Validity of Inertial Measurement Units to Quantify Average and Peak Acceleration Values.

The increasing interest in assessing physical demands in team sports has led to the development of multiple sports related monitoring systems. Due to technical limitations, these systems primarily could be applied to outdoor sports, whereas an equivalent indoor locomotion analysis is not established yet. Technological development of inertial measurement units (IMU) broadens the possibilities for player monitoring and enables the quantification of locomotor movements in indoor environments. The aim of the current study was to validate an IMU measuring by determining average and peak human acceleration under indoor conditions in team sport specific movements. Data of a single wearable tracking device including an IMU (Optimeye S5, Catapult Sports, Melbourne, Australia) were compared to the results of a 3D motion analysis (MA) system (Vicon Motion Systems, Oxford, UK) during selected standardized movement simulations in an indoor laboratory (n = 56). A low-pass filtering method for gravity correction (LF) and two sensor fusion algorithms for orientation estimation [Complementary Filter (CF), Kalman-Filter (KF)] were implemented and compared with MA system data. Significant differences (p < 0.05) were found between LF and MA data but not between sensor fusion algorithms and MA. Higher precision and lower relative errors were found for CF (RMSE = 0.05; CV = 2.6%) and KF (RMSE = 0.15; CV = 3.8%) both compared to the LF method (RMSE = 1.14; CV = 47.6%) regarding the magnitude of the resulting vector and strongly emphasize the implementation of orientation estimation to accurately describe human acceleration. Comparing both sensor fusion algorithms, CF revealed slightly lower errors than KF and additionally provided valuable information about positive and negative acceleration values in all three movement planes with moderate to good validity (CV = 3.9 – 17.8%). Compared to x- and y-axis superior results were found for the z-axis. These findings demonstrate that IMU-based wearable tracking devices can successfully be applied for athlete monitoring in indoor team sports and provide potential to accurately quantify accelerations and decelerations in all three orthogonal axes with acceptable validity. An increase in accuracy taking magnetometers in account should be specifically pursued by future research.

Validation of Inertial Measurement Units for Upper Body Kinematics.

The purpose of this study was to validate a commercially available inertial measurement unit (IMU) system against a standard lab-based motion capture system for the measurement of shoulder elevation, elbow flexion, trunk flexion/extension, and neck flexion/extension kinematics. The validation analyses were applied to 6 surgical faculty members performing a standard, simulated surgical training task that mimics minimally invasive surgery. Three-dimensional joint kinematics were simultaneously recorded by an optical motion capture system and an IMU system with 6 sensors placed on the head, chest, and bilateral upper and lower arms. The sensor-to-segment axes alignment was accomplished manually. The IMU neck and trunk IMU flexion/extension angles were accurate to within 2.9 ± 0.9 degrees and 1.6 ± 1.1°, respectively. The IMU shoulder elevation measure was accurate to within 6.8 ± 2.7° and the elbow flexion measure was accurate to within 8.2 ± 2.8°. In the Bland-Altman analyses, there were no significant systematic errors present; however, there was a significant inversely proportional error across all joints. As the gold standard measurement increased, the IMU underestimated the magnitude of the joint angle. This study reports acceptable accuracy of a commercially available IMU system; however, results should be interpreted as protocol specific.

Static and dynamic validation of inertial measurement units

Optical motion capture systems are used to assess human motion. While these systems provide a reliable analysis, they limit collection to a laboratory based setting. Devices such as Inertial Measurement Units (IMUs) have been developed as alternative tools. Commercially available IMUs are utilized for a variety of applications; however limited work has been done to determine the reliability of these devices. The objective of this study was to assess the accuracy and precision of a commercially available IMU, containing tri-axial accelerometers, gyroscopes, and magnetometers, under controlled static and dynamic conditions. The sensor output was validated against the gold standard measures of custom made mechanical testing apparatuses. The IMUs provide an accurate (within 0.6°) and precise (within 0.1°) measurement of static sensor orientation and an accurate (within 4.4° per second) and precise (within 0.2° per second) representation of angular velocity. The sensors are more accurate at lower velocities, but the percent error remains relatively constant across all angular velocities. Inclusion of IMUs as an appropriate measurement tool should be based on the application, specific demands and necessary reliability.

Validation of inertial measurement units with an optoelectronic system for whole-body motion analysis.

The potential of inertial measurement units (IMUs) for ergonomics applications appears promising. However, previous IMUs validation studies have been incomplete regarding aspects of joints analysed, complexity of movements and duration of trials. The objective was to determine the technological error and biomechanical model differences between IMUs and an optoelectronic system and evaluate the effect of task complexity and duration. Whole-body kinematics from 12 participants was recorded simultaneously with a full-body Xsens system where an Optotrak cluster was fixed on every IMU. Short functional movements and long manual material handling tasks were performed and joint angles were compared between the two systems. The differences attributed to the biomechanical model showed significantly greater (P≤.001) RMSE than the technological error. RMSE was systematically higher (P≤.001) for the long complex task with a mean on all joints of 2.8° compared to 1.2° during short functional movements. Definition of local coordinate systems based on anatomical landmarks or single posture was the most influent difference between the two systems. Additionally, IMUs accuracy was affected by the complexity and duration of the tasks. Nevertheless, technological error remained under 5° RMSE during handling tasks, which shows potential to track workers during their daily labour.