Neuromuscular and Movement Control Strategies With Soft Passive Low Back Exoskeleton Use During EMS-Specific Physical Agility Tests

Abstract

Emergency Medical Technicians (EMTs) are at high risk of work-related low back injuries due to the physical demands of patient rescue and transfer operations. Despite training in proper lifting techniques and ergonomic interventions, there remains a gap in technology that can assist EMTs without hindering their movement or attention. Soft-passivelow- back exoskeletons (LBEs) are a potential solution. Previous research on LBEs has shown reduced muscular demands in the lower back, but studies have been limited to static holding or sagittal plane lifting. Our study investigates the use of a soft LBE in a dynamic work environment with physically and mentally demanding tasks, similar to those performed by EMTs. We evaluated the neuromuscular, kinematic, and subjective differences between control and exoskeleton conditions. Results indicated lowered muscular demands and improved kinematics however these benefits were task-specific. Interestingly, there was a mismatch between subjective perception of workload and effort during and after the tasks where EMTs were not able to recognize the benefits during the tasks.

Extended Abstract

Emergency Medical Technicians and Paramedics (EMTs) are at a significantly higher risk of work-related low back injuries due to occupational demands of tasks related to patient rescue and transfer operations place (Friedenberg et al., 2022). Tasks such as lifting beyond permissible limits, repetitive bending and rescuing in confined spaces place significant strain on their musculoskeletal systems. Although EMT-Ps are trained in proper lifting techniques and the use of ergonomic interventions such as automatic and adjustable stretchers, there remains a gap in the available technology that can promptly assist EMT-Ps without disturbing their movement, environment, and attention. Soft passive low-back exoskeletons (LBEs) are a potential solution to address this gap. Previous research on soft passive LBEs has shown a reduction in muscular demands in the lower back (Toxiri et al., 2019). However, these studies are limited to static holding or dynamic lifting in the sagittal plane. Therefore, our study aims to investigate the use of a soft passive LBE for variable dynamic work domain with highly physically and mentally demanding tasks with a varied range of motion, such as those performed by EMT. To achieve this, we used a modified version of the physical agility tests that consist of tasks commonly performed by EMTs in the field. These tasks were performed in a circuit to mimic the real-world applicability in the present work. The primary objective of this study was to evaluate the neuromuscular, biomechanical, and subjective perceptions of cognitive and physical demands with LBE use. We hypothesized that with exoskeleton use there would be reduced muscular load on the lower back. Next, we also hypothesized that the movement quality would differ with LBE use due to lowered muscular demands and different postural control strategies. However, we hypothesize that the effects will be task-specific, given that all tasks may not require exoskeleton assistance or that more dynamic movements may reduce exoskeleton benefits. Our results show muscle activity for erector spinae and bicep femoris reduced with exoskeleton use for one-hand carry (23%–29%), barbell carry (7%–20%), stretcher push/pull (18%), and CPR (38%–53%), which aligns well with our first hypothesis. Furthermore, a ~40% increase in the hip ROM during one-hand carry suggests that the LBE might have engaged with the hip adductors, potentially helping EMT-Ps to improve their limb support (Lyons et al., 1983). This adjustment possibly helped with the redistribution of load, as seen by reduced activation in the left bicep femoris. Additionally, the decrease in the acceleration of the lower limbs suggests exoskeleton use is beneficial for reducing jerky movement, enabling more controlled motion (Kavanagh & Menz, 2008). We notice similar results for barbell carry and stretcher push/pull tasks. Interestingly, we observe increased static loading of the right anterior deltoid (~67%) during the first backboard lift. While no postural differences were observed and RPD results indicated reduced discomfort in the lower back and shoulder with LBE use, it is likely that the static loading of the deltoids may be a compensatory mechanism for movement control. A ~31% exoskeleton-related increase in the peak acceleration of the left upper arm for CPR was accompanied by reductions in the knee ROM and peak activation for the biceps femoris. CPR requires significant upper body motions for effective chest pumping in a kneeled crouched posture (Krikscionaitiene et al., 2013). That the performance between the exoskeleton conditions was similar is indicative of different movement strategies adopted by EMT-Ps to ensure quality CPR performance. Despite comparable ratings of RPE and MD, and performance during each PAT task, lower physical and temporal demand and effort were reported with LBE use. This highlights some gaps in wearers not recognizing the benefits of LBEs in reducing effort, despite acknowledging lower discomfort with no change in mental demands.