Validation of an Embedded Motion-Capture and EMG Setup for the Analysis of Musculoskeletal Disorder Risks during Manhole Cover Handling

Musculoskeletal disorders in the workplace are a growing problem in Europe. The measurement of these disorders in a working environment presents multiple limitations concerning equipment and measurement reliability. The aim of this study was to evaluate the use of inertial measurement units against a reference system for their use in the workplace. Ten healthy volunteers conducted three lifting methods (snatching, pushing, and pulling) for manhole cover using a custom-made tool weighting 20 and 30 kg. Participants’ back and dominant arm were equipped with IMU, EMG, and reflective markers for VICON analysis and perception of effort was estimated at each trial using a Visual Analog Scale (VAS). The Bland–Altman method was used and results showed good agreement between IMU and VICON systems for Yaw, Pitch and Roll angles (bias values < 1, −4.4 < LOA < 3.6°). EMG results were compared to VAS results and results showed that both are a valuable means to assess efforts during tasks. This study therefore validates the use of inertial measurement units (IMU) for motion capture and its combination with electromyography (EMG) and a Visual Analogic Scale (VAS) to assess effort for use in real work situations.

Stride Lengths during Maximal Linear Sprint Acceleration Obtained with Foot-Mounted Inertial Measurement Units

Inertial measurement units (IMUs) fixed to the lower limbs have been reported to provide accurate estimates of stride lengths (SLs) during walking. Due to technical challenges, validation of such estimates in running is generally limited to speeds (well) below 5 m·s−1. However, athletes sprinting at (sub)maximal effort already surpass 5 m·s−1 after a few strides. The present study aimed to develop and validate IMU-derived SLs during maximal linear overground sprints. Recreational athletes (n = 21) completed two sets of three 35 m sprints executed at 60, 80, and 100% of subjective effort, with an IMU on the instep of each shoe. Reference SLs from start to ~30 m were obtained with a series of video cameras. SLs from IMUs were obtained by double integration of horizontal acceleration with a zero-velocity update, corrected for acceleration artefacts at touch-down of the feet. Peak sprint speeds (mean ± SD) reached at the three levels of effort were 7.02 ± 0.80, 7.65 ± 0.77, and 8.42 ± 0.85 m·s−1, respectively. Biases (±Limits of Agreement) of SLs obtained from all participants during sprints at 60, 80, and 100% effort were 0.01% (±6.33%), −0.75% (±6.39%), and −2.51% (±8.54%), respectively. In conclusion, in recreational athletes wearing IMUs tightly fixed to their shoes, stride length can be estimated with reasonable accuracy during maximal linear sprint acceleration.

Minimum Settings Calibration Method for Low-Cost Tri-Axial IMU and Magnetometer

This manuscript presents a minimum settings calibration method for low-cost tri-axial inertial measurement units (IMU) and magnetometers. At first, we analyze the major defect of the traditional calibration methods for tri-axial accelerometers and magnetometers. To fix that problem, we just utilize the ellipsoid model to calibrate the tri-axial accelerometer and magnetometer preliminarily, then complete the calibration work with at least two reference angular positions, and prove that two reference angular positions are minimum requirements in the calibration progress. Next, the tri-axial gyroscope is calibrated based on the nonlinear cost function with the aid of the pre-calibrated accelerometer. The simulation and real-world experiment results show that the proposed method is practical and effective, suggesting that this technique is a viable candidate for the IMU and magnetometer applications.

Pilot-study of ridden walk on the circle – effects of progressive collection and lateral exercises

When collecting the horse, the rider influences stride length, forehand/hindquarters balance, and head-neck position. The study aim was to describe the vertical excursion of the withers and croup, and the sagittal cannon angles during collection and lateral exercises. Ten horses were ridden by five riders during 14 trials (1-5 per rider) on 10 m circles. Each trial included free walk, four degrees of increasing collection, and haunches-in and shoulderin. Inertial measurement units (100 Hz) were positioned on the withers, the first sacral vertebra (S1) and laterally on the cannons. Data for each exercise were stride-split. Range of motion (ROM), minima and maxima were studied in mixed models, controlling for stride duration. S1 vertical ROM ranged between 30-32 mm (highest degree of collection) and 51 mm (free walk), significantly smaller with increasing collection. S1 ROM during the inside hind limb step was smaller in haunches-in and shoulder-in compared to at the lowest degree of collection. Withers ROM ranged between 12 mm (lowest degree of collection) and 16-18 mm (highest degree of collection). Fore cannon protraction-retraction ROM ranged between 57° (highest degree of collection) and 63° (free walk). Hind cannon protraction-retraction ROM ranged between 47-50° (highest degree of collection) and 51-56° (free walk). All limbs had significantly smaller ROM at the highest degree of collection. Cannon ROMs were smaller for the outer limbs in haunches-in, and all limbs but the outer fore in shoulder-in, compared to the lowest degree of collection. Progressively decreasing ROM for fore- and hind limb cannons and S1 suggest that the riders achieved a shortening of the gait at higher degrees of collection. In shoulder-in and haunches-in, the diagonal oriented in the direction of motion showed decreased hind limb cannon ROM while forelimb cannon ROM was maintained, which could suggest increased shoulder freedom and collection of the targeted diagonal.