Andrea Giovanardi

A simple test to assess the static and dynamic accuracy of an inertial sensors system for human movement analysis

In the present study we introduced a simple test to assess the orientation error of an inertial sensors system for human movement analysis, both in static and dynamic conditions. In particular, the test was intended to quantify the sensitivity of the orientation error to direction and velocity of rotation. The test procedure was performed on a 5 MT9B sensors Xsens acquisition system, and revealed that the system orientation error, expressed by Euler angles decomposition, was sensitive both to direction and to velocity, being higher for fast movements: for mean rotation velocities of 180deg/s and 360deg/s, the worst case orientation error was 5.4deg and 11.6deg, respectively. The test can be suggested therefore as a useful tool to verify the user specific system accuracy without requiring any special equipment. In addition, the test provides further error information concerning direction and velocity of the movement which are not supplied by the producer, since they depend on the specific field of application

Assessment of three-dimensional joint kinematics of the upper limb during simulated swimming using wearable inertial-magnetic measurement units

ABSTRACT The analysis of the joint kinematics during swimming plays a fundamental role both in sports conditioning and in clinical contexts. Contrary to the traditional video analysis, wearable inertial-magnetic measurements units (IMMUs) allow to analyse both the underwater and aerial phases of the swimming stroke over the whole length of the swimming pool. Furthermore, the rapid calibration and short data processing required by IMMUs provide coaches and athletes with an immediate feedback on swimming kinematics during training. This study aimed to develop a protocol to assess the three-dimensional kinematics of the upper limbs during swimming using IMMUs. Kinematics were evaluated during simulated dry-land swimming trials performed in the laboratory by eight swimmers. A stereo-photogrammetric system was used as the gold standard. The results showed high coefficient of multiple correlation (CMC) values, with median (first–third quartile) of 0.97 (0.93–0.95) and 0.99 (0.97–0.99) for simulated front-crawl and breaststroke, respectively. Furthermore, the joint angles were estimated with an accuracy increasing from distal to proximal joints, with wrist indices showing median CMC values always higher than 0.90. The present findings represent an important step towards the practical use of technology based on IMMUs for the kinematic analysis of swimming in applied contexts.

Gait Kinematic Analysis in Water Using Wearable Inertial Magnetic Sensors.

Walking is one of the fundamental motor tasks executed during aquatic therapy. Previous kinematics analyses conducted using waterproofed video cameras were limited to the sagittal plane and to only one or two consecutive steps. Furthermore, the set-up and post-processing are time-consuming and thus do not allow a prompt assessment of the correct execution of the movements during the aquatic session therapy. The aim of the present study was to estimate the 3D joint kinematics of the lower limbs and thorax-pelvis joints in sagittal and frontal planes during underwater walking using wearable inertial and magnetic sensors. Eleven healthy adults were measured during walking both in shallow water and in dry-land conditions. Eight wearable inertial and magnetic sensors were inserted in waterproofed boxes and fixed to the body segments by means of elastic modular bands. A validated protocol (Outwalk) was used. Gait cycles were automatically segmented and selected if relevant intraclass correlation coefficients values were higher than 0.75. A total of 704 gait cycles for the lower limb joints were normalized in time and averaged to obtain the mean cycle of each joint, among participants. The mean speed in water was 40% lower than that of the dry-land condition. Longer stride duration and shorter stride distance were found in the underwater walking. In the sagittal plane, the knee was more flexed (≈ 23°) and the ankle more dorsiflexed (≈ 9°) at heel strike, and the hip was more flexed at toe-off (≈ 13°) in water than on land. On the frontal plane in the underwater walking, smoother joint angle patterns were observed for thorax-pelvis and hip, and ankle was more inversed at toe-off (≈ 7°) and showed a more inversed mean value (≈ 7°). The results were mainly explained by the effect of the speed in the water as supported by the linear mixed models analysis performed. Thus, it seemed that the combination of speed and environment triggered modifications in the joint angles in underwater gait more than these two factors considered separately. The inertial and magnetic sensors, by means of fast set-up and data analysis, can supply an immediate gait analysis report to the therapist during the aquatic therapy session.

Aquatic Therapy after Anterior Cruciate Ligament Surgery: A Case Study on Underwater Gait Analysis using Inertial and Magnetic Sensors

Background: Water exercise is employed as therapeutic treatment. The reduction of the body weight and the increased resistance to the movement are two representative and desirable effects of the underwater gait advantages. The aim of the present study was to propose a movement analysis methodology based on inertial and magnetic sensors to provide quantitative data on the joint kinematics of an anterior cruciate ligament injured patient. Methods: One patient operated on reconstruction of the anterior cruciate ligament performed three 10-meters-long walking trials, in dry-land and underwater conditions. A validated motion analysis protocol was used to analyze the participant 3D joint kinematics of the lower limbs during walking task, using inertial and magnetic sensors. Angular and spatio-temporal variables of hips, knees and ankles were calculated for each side. Gait patterns of healthy subjects, assumed as control group, were chosen among literature as reference. Results: The injured limb had a smaller knee flexion than that of the controlateral limb. The patient gait patterns showed differences with respect to the control group in both environmental conditions. In the underwater walking the patient gait patterns were more similar to those of the control group than in dryland walking. The range of motion for the injured and the controlateral limbs were generally larger in the underwater condition rather than in dry-land condition. Conclusion: This case study underlines that walking in underwater condition can lead an anterior cruciate ligament injured patient to increase the knee flexion-extension range of motion, and simultaneously to assume gait patterns more similar to those of the control group. As consequence of these results, this case-study enhanced the usability of the method described to provide quantitative gait data, and provided preliminary information that might be considered as a first reference for further investigations on the walking kinematics of anterior cruciate ligament injured patients.

The Use of IMMUs in a Water Environment: Instrument Validation and Application of 3D Multi-Body Kinematic Analysis in Medicine and Sport

The aims of the present study were the instrumental validation of inertial-magnetic measurements units (IMMUs) in water, and the description of their use in clinical and sports aquatic applications applying customized 3D multi-body models. Firstly, several tests were performed to map the magnetic field in the swimming pool and to identify the best volume for experimental test acquisition with a mean dynamic orientation error lower than 5°. Successively, the gait and the swimming analyses were explored in terms of spatiotemporal and joint kinematics variables. The extraction of only spatiotemporal parameters highlighted several critical issues and the joint kinematic information has shown to be an added value for both rehabilitative and sport training purposes. Furthermore, 3D joint kinematics applied using the IMMUs provided similar quantitative information than that of more expensive and bulky systems but with a simpler and faster setup preparation, a lower time consuming processing phase, as well as the possibility to record and analyze a higher number of strides/strokes without limitations imposed by the cameras.