IMPROVING THE ACCURACY OF LOW-COST GNSS BY FUSION WITH INERTIAL AND MAGNETIC SENSORS IN ALPINE SKI RACING

For analysing performance in alpine ski racing, an accurate estimation of the skier's centre of mass trajectory and speed is indispensable. However, the sole use of low-cost GNSS might not be accurate enough to detect meaningful differences. The aim of this study was to introduce a new system that can improve the accuracy of a low-cost GNSS to an acceptable level. To this end, the data obtained by low-cost GNSS was fused with data form inertial sensors and position information of permanent magnets buried into the snow surface along the ski track. This fusion improved the system's accuracy from 2m to 0.5m. Despite the added sensing technologies, the system remained simple and was easy to use. Further improvements are possible and a technical validation of the system could be a major aim for the future

Smart knee prosthesis kinematics estimation and validation in a robotic knee simulator

In this work we present the smart knee prosthesis designed for in-vivo kinematics measurement and its validation in two knee simulators, i.e. a robotic knee simulator to provide realistic condition, and a manual simulator with more degrees of freedom. The sensor configuration including three magnetic sensors was designed, and the machine learning techniques were used to translate the magnetic measurements to knee rotations. First the concurrent flexion-extension and internal-external rotations were estimated via linear and nonlinear estimators, and technically validated in a manual knee simulator against motion capture system. Then the flexion-extension estimation was validated in a robotic knee simulator providing the realistic sagittal kinematics of treadmill and over-ground walking. The obtained results showed the high accuracy and precision of the estimates

CONCURRENT ASSESSMENT OF SYMMETRY, VARIABILITY, AND COMPLEXITY OF STRIDE DURING PROLONGED OUTDOOR RUNNING

The aim of this study was to analyse the influence of acute fatigue on the asymmetry, variability, and complexity of the running pattern. We equipped 11 half-marathon participants with an inertial measurement unit (IMU) on each foot and a global navigation satellite system (GNSS)-IMU sensor on chest. Every 10 minutes of the race, the participant pronounced their perceived rating-of-fatigue (ROF) on a scale of 1 to 10. We divided the race into 8 equal segments, with one ROF score per segment, and included only the flat running parts. Temporal gait parameters were extracted using validated algorithms, followed by the computation of their asymmetry, and the variability and complexity of the cycle time (CT). Gait asymmetry increased significantly toward the end of the race and at higher perceived fatigue; faster runners showed a greater increase in asymmetry. CT variability increased significantly at the beginning of the race and then remained stable for all participants, but faster runners showed up to 20% less variability. No significant change was observed in CT complexity. This study highlights the increase in asymmetry and variability due to acute fatigue, with differences between fast/slow runners, and the importance of simultaneously measuring perceived fatigue and gait parameters under real-world conditions

Detection of the movement of the humerus during daily activity

A new ambulatory technique for qualitative and quantitative movement analysis of the humerus is presented. 3D gyroscopes attached on the humerus were used to recognize the movement of the arm and to classify it as flexion, abduction and internal/external rotations. The method was first validated in a laboratory setting and then tested on 31 healthy volunteer subjects while carrying the ambulatory system during 8h of their daily life. For each recording, the periods of sitting, standing and walking during daily activity were detected using an inertial sensor attached on the chest. During each period of daily activity the type of arm movement (flexion, abduction, internal/external rotation) its velocity and frequency (number of movement/hour) were estimated. The results showed that during the whole daily activity and for each activity (i.e. walking, sitting and walking) the frequency of internal/external rotation was significantly higher while the frequency of abduction was the lowest (P<0.009). In spite of higher number of flexion, abduction and internal/external rotation in the dominant arm, we have not observed in our population a significant difference with the non-dominant arm, implying that in healthy subjects the arm dominance does not lie considerably on the number of movements. As expected, the frequency of the movement increased from sitting to standing and from standing to walking, while we provide a quantitative value of this change during daily activity. This study provides preliminary evidence that this system is a useful tool for objectively assessing upper-limb activity during daily activity. The results obtained with the healthy population could be used as control data to evaluate arm movement of patients with shoulder diseases during daily activit

TRUNK MOTION DURING A HALF-MARATHON: THE IMPACT OF PERCEIVED FATIGUE ON MOTION STABILITY AND SMOOTHNESS

Our objective was to investigate the effects of acute fatigue on stability and smoothness of trunk motion during a half marathon. 13 recreational runners were fitted with a GNSS-IMU sensor on their chest. Every 10 minutes of the race, the participant pronounced their perceived fatigue, recorded by a smartphone attached to the arm. We divided the race into 8 equal segments, corresponding to one fatigue score per segment, and considered only level running. Based on mediolateral acceleration and running velocity (v), stability was characterized by spectral entropy, RMS of acceleration (RMSA), and autocorrelation between successive steps and strides; smoothness by jerk cost (JC), spectral arc length (SPARC), and inverse number of peaks (IPV) of v. Both RMSA and JC increased significantly shortly after race onset. RMSA increased significantly at a lower perceived fatigue level, while JC increased at a higher level. Whereas other measures did not change substantially, RMSA and JC showed a clear change with acute fatigue and also differentiated well between the five fastest and five slowest runners. With increasing perceived fatigue, both parameters showed a higher change for ‘slow’ group. This study highlights the loss of stability and smoothness in running due to acute fatigue and the importance of simultaneously measuring perceived fatigue and trunk biomechanics under real-world conditions

SWIMMING PHASE-BASED PERFOMANCE EVALUATION USING A SINGLE IMU IN FRONT CRAWL

The purpose of this study was to assess the potential of using a sacrum-worn inertial measurement unit (IMU) for performance evaluation in each swimming phase (wall push-off, glide, stroke preparation, and swimming) of national-level swimmers in front crawl technique. Nineteen swimmers were asked to wear a sacrum IMU and swim four one-way 25-m trials in front crawl, attached to a tethered speedometer and filmed by cameras in the whole lap for validation. Based on the literature, several goal metrics were defined over speedometer data, each one representing the performance of the swimmer either in one phase (maximum velocity of wall push-off phase) or several phases (time of 15 meters for wall push-off, glide, stroke preparation phases). Following a macro-micro approach, the IMU parameters of each swimming phase were used to predict the goal metrics. The selected IMU parameters were in line with the characteristics of movement within each phase and can estimate the corresponding goal metric with an R2 over 0.8 and relative RMSE lower than 10%

Stride count and frequency measured with a wrist-worn inertial sensor

This study proposes three simple approaches to estimate the stride count and frequency during walking and running using an inertial measurement system on the wrist. The approaches were based on a time-domain, frequency-domain and autocorrelation analysis, respectively. They were compared and validated against a reference on walks and runs of 16 participants in different conditions (different speeds, over ground and on treadmill). Results showed that the three methods provided an accurate and precise measure of the stride count and frequency: the median stride count error was 1 stride with a 90% confidence interval of 4 strides and the stride frequency presented a median error of 0.03 strides/min with a 90% confidence interval lower than 1.5 strides/min for all three methods. The approach, based on a wrist-worn inertial sensor, offers an effective and simple way to quantify the strides of healthy subjects in various conditions