Accuracy of identification of low or high risk lifting during standardised lifting situations

Abstract

The aim was to classify lifting activities into low and high risk categories (according to The Danish Working Environment Authority guidelines) based on surface electromyography (sEMG) and trunk inclination (tri-axial accelerometer) measurements. Lifting tasks with different weights, horizontal distance and technique were performed. The lifting tasks were characterised by a feature vector composed of either the 90th, 95th or 99th percentile of sEMG activity level and trunk inclinations during the task. Linear Discriminant Analysis and a subject-specific threshold scheme were applied and lifting tasks were classified with an accuracy of 65.1-65.5%. When lifts were classified based on the subject-specific threshold scheme from low and upper back accelerometers, the accuracy reached 52.1-58.1% and 72.7-78.1%, respectively. In conclusion, the use of subject-specific thresholds from sEMG from upper trapezius and erector spinae as well as inclination of the upper trunk enabled us to identify low and high risk lifts with an acceptable accuracy.Practitioner Summary: This study contributes to the development of a method enabling the automatic detection of high risk lifting tasks, i.e. exposure to high biomechanical loads, based on individual sEMG and kinematics from an entire working day. These methods may be more costeffective and may complement observations commonly used by practitioners.

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“…We have previously shown that the intra-day reliability for sEMG during lifting tasks is acceptable in laboratory conditions [26]. Furthermore, the method for detecting events of the lower back and shoulder based on sEMG and IMU from the upper back has shown high accuracy in a laboratory setng [25].…”

“…The analyses for detecting the events are described in detail elsewhere [25]. In short, the sEMG segments corresponding to the references lifts and the MVC trials were extracted.…”

“…The sEMG, IMU, and camera were synchronized [25] while the heart rate monitor was used to estimate the overall activity level during the working day.…”

“…The procedure for placement of sEMG electrodes is described elsewhere [23,25,26]. The sEMG electrodes (Blue Sensor N-00-S/25, Ambu A/S, Ballerup, Denmark) were placed bilaterally over the erector spinae and the upper trapezius muscles [27] according to the SENIAM recommendations [28].…”

“…The synchronization with the cameras was obtained by having the cameras record a custom-made flashing device which flashed at the same time as the signal was sent to the sEMG logger box and the rotary solenoid. The synchronization was made before the equipment was positioned on the participant and repeated after the working day [25].…”